Process For Producing Thermoplastic Polymer Compositions With Optimized Degree Of Crosslinking Patent Application (2024)

U.S. patent application number 15/560312 was filed with the patent office on 2018-03-08 for process for producing thermoplastic polymer compositions with optimized degree of crosslinking.The applicant listed for this patent is INEOS STYROLUTION GROUP GMBH. Invention is credited to Brian J. BANASZAK, Johannes BARTH, Gisbert MICHELS, Nikolaus NESTLE, Libor SEDA, Roland WALKER.

Application Number20180066117 15/560312
Document ID /
Family ID52706107
Filed Date2018-03-08
United States PatentApplication20180066117
Kind CodeA1
BANASZAK; Brian J. ; etal.March 8, 2018

PROCESS FOR PRODUCING THERMOPLASTIC POLYMER COMPOSITIONS WITHOPTIMIZED DEGREE OF CROSSLINKING

Abstract

A process produces a polymer composition (A) containing astyrene copolymer (a) and an impact modifier (b), comprising acopolymer (b1) as graft base and a graft (b2), where the steps ofthe process are: (1) providing a crosslinked copolymer (b1) madeof: (b11) from 70 to 99.99% by weight of a conjugated diene oracrylate, (b12) from 0 to 29% by weight of another comonomer, (b13)from 0 to 10% by weight of crosslinking monomers, and (b14) from0.01 to 0.7% by weight of a chain-transfer reagent; (2) applying,to the copolymer (b1), at least one graft (b2) comprising: (b21)from 65 to 95% by weight of a vinylaromatic monomer, (b22) from 5to 35% by weight of acrylonitrile and/or methacrylonitrile, and(b23) from 0 to 30% by weight of monoethylenically unsaturatedmonomers, thus providing the impact modifier (b); (3) mixing thestyrene copolymer (a) and the impact modifier (b), and thus leadsto improved mechanical properties of the polymer composition(A).

Inventors:BANASZAK; Brian J.;(Mannheim, DE) ; WALKER; Roland; (Osnabrueck,DE) ; SEDA; Libor; (Karlovy Vary, CZ) ; BARTH;Johannes; (Ludwigshafen, DE) ; MICHELS; Gisbert;(Leverkusen, DE) ; NESTLE; Nikolaus; (Heidelberg,DE)
Applicant:
NameCityStateCountryType

INEOS STYROLUTION GROUP GMBH

Frankfurt am Main

DE
Family ID:52706107
Appl. No.:15/560312
Filed:March 23, 2016
PCT Filed:March 23, 2016
PCT NO:PCT/EP2016/056344
371 Date:September 21, 2017
Current U.S.Class:1/1
Current CPCClass:C08F 279/04 20130101;C08L 55/02 20130101; C08L 25/12 20130101; C08F 2/26 20130101; C08J3/24 20130101; G01R 33/46 20130101; C08F 2/38 20130101; C08J2300/22 20130101; C08L 55/02 20130101; C08L 25/12 20130101; C08L25/12 20130101; C08L 55/02 20130101; C08F 279/04 20130101; C08F220/44 20130101; C08F 279/04 20130101; C08F 212/08 20130101
InternationalClass:C08J 3/24 20060101C08J003/24; C08F 2/26 20060101 C08F002/26; C08F 2/38 20060101C08F002/38; C08F 279/04 20060101 C08F279/04; C08L 25/12 20060101C08L025/12; C08L 55/02 20060101 C08L055/02

Foreign Application Data

DateCodeApplication Number
Mar 25, 2015EP15160878.3

Claims

1-14. (canceled)

15. A process for optimizing the degree of crosslinking (V) of acrosslinked copolymer (b1) as graft substrate for a polymericimpact modifier (b) produced from a monomer mixture comprising:(b11): 70 to 99.99 wt % of at least one conjugated diene and/or ofat least one acrylate, (b12): 0 to 29 wt % of at least one furthercomonomer selected from: styrene, .alpha.-methylstyrene,acrylonitrile, methacrylonitrile, and methyl methacrylate, (b13): 0to 10 wt % of one or more polyfunctional crosslinking monomers, and(b14): 0.01 to 0.7 wt % of a chain transfer agent, based on theentire monomer quantity of the polymerization mixture for producingsaid copolymer (b1); wherein the process comprises the steps of:(i) polymerizing the monomer mixture for producing said copolymer(b1); (ii) determining via NMR relaxation measurements the degreeof crosslinking (V) of said copolymer (b1) obtained in step (i);(iii) polymerizing a modified monomer mixture to produce a modifiedcopolymer (b1'), wherein the parameters of the polymerizationreaction are adapted according to said crosslinking (V) determinedas per step (ii) for said copolymer (b1) and according to thedesired crosslinking (V') of said copolymer (b1') as graftsubstrate; and (iv) repeating said steps (i) to (iii) as often asnecessary until a desired degree of crosslinking (V') is obtained,and wherein the transversal relaxation time T2 is used to determinesaid degree of crosslinking (V) of said copolymer (b1), said degreeof crosslinking (V) of said copolymer (b1) is determined by using alow-field NMR spectrometer at a field strength ranging from 0.001to 1.5 teslas, preferably from 0.1 to 0.6 tesla, and the T2 timesfor said graft substrates (b1) are in the range from 2.0 to 7 ms,as measured on filmed samples at 140.degree. C.

16. The process as claimed in claim 15, characterized in that thestep of providing said copolymer (b1') according to said degree ofcrosslinking (V) determined in step (ii) for said copolymer (b1)resulting from the first polymerization reaction is carried out byadmixing the reaction mixture of the polymerization mixture as perstep (iii) additionally with a polyfunctional crosslinking monomer(b13) as crosslinking agent and/or a chain transfer agent (b14), orchanging the reaction temperature in the polymerization reaction,or a combination thereof.

17. The process as claimed in claim 15, characterized in that thestep of providing said copolymer (b1') is carried out by subjectingthe reaction mixture of the polymerization reaction to atemperature change by not less than 10.degree. C.

18. The process as claimed in claim 15, characterized in that thereaction mixture has added to it a chain transfer agent in anamount of 0.1 to 0.6 wt %, based on the entire monomer quantity ofthe polymerization mixture for producing said copolymer (b1').

19. The method of using the process as claimed in claim 15 in themanufacture of a copolymer (b1') having an optimized degree ofcrosslinking (V').

Description

[0001] The invention relates to a process for producingthermoplastic polymer compositions (molding compounds) having anoptimized degree of crosslinking. More particularly, the inventionconcerns a process for producing copolymers, especially graftcopolymers, having an optimized degree of crosslinking.

[0002] It has been known for decades to produce thermoplasticpolymer compositions by modifying thermoplastic polymers throughincorporation of elastomers (rubbers) in order to thus obtainimpact-modified thermoplastic compositions. This is accomplishedfor example by graft interpolymerization of styrene andacrylonitrile in the presence of a rubber and also by subsequentblending of this graft copolymer with a separately producedpolymeric matrix which may for example consist of astyrene-acrylonitrile copolymer or a methylstyrene-acrylonitrilecopolymer.

[0003] Elastomers are dimensionally stable, recovering elasticallyfrom any deformation. Their glass transition point is below thenormal temperature of service. These properties are the result ofthe individual polymeric chains of the elastomer being linkedtogether by covalent bonds. The polymer is then said to becrosslinked. Its degree of crosslinking is determinative for theproperties of the polymer. An increasing degree of crosslinking, incomparable systems, is observed to make the materials stiffer,harder and more resistant to corrosion, but in return also toacquire rather less desirable properties, such as brittleness.Elastomers are polymers having a middling degree of crosslinking,whereas thermoplastics frequently have a low and thermosets a highdegree of crosslinking.

[0004] The degree of crosslinking is a quantitative measure forcharacterizing polymeric networks. It is for example computed asthe quotient formed by dividing the moles of crosslinked basicbuilding blocks by the moles of all the basic building blockspresent in this macromolecular product (network).

[0005] The degree of crosslinking is reported either as adimensionless number or in percent (amount-of-substance fraction).The degree of crosslinking must not be confused with the crosslinkdensity of a polymer: the number of crosslinks per unit volume.

[0006] A polymer's maximum degree of crosslinking is derivable fromthe formulation for the polymeric network. This maximum degree ofcrosslinking represents a theoretical degree of crosslinking, as itis almost never attained in practice, since during thepolymerization (network formation), not all the building blockscapable of crosslinking actually find an entity to react with,inter alia because of steric hindrance, and the rest of thereaction conditions may also affect the crosslinking.

[0007] The theoretical degree of crosslinking computes from thecomposition of the monomer mixture. The actually attained degree ofcrosslinking is analytically determinable, for example viaspectroscopic methods, such as NMR spectroscopy (cf. K.Saalwachter, Progress in Nuclear Magnetic Resonance Spectroscopy,2007, 51, pp. 1-35; R. Kimmich, N. Fatkullin, Advances in PolymerScience, 2004, 170, pp. 1-113), after the polymerization.

[0008] WO 2013/060914 relates to the characterization of anelastomeric latex via low-field NMR spectroscopy. Double quantumcoherence spectroscopy is used therein to study natural rubberlatices for their network structure as the natural rubber undergoesvarious processing operations.

[0009] Analytica Chimica Acta, vol. 604, 2007, pages 54-61describes the study of styrene-butadiene-styrene block copolymersvia low-field time domain NMR spectroscopy.

[0010] To be able to produce elastomers having specific propertiesin a planful manner, therefore, the process for producingcrosslinked polymers must be precisely controllable. Since a largenumber of factors affect the crosslinking reactions, this may beaccomplished in various ways, for example by controlling thereaction temperature or by admixing molecular weight regulatorssuch as, for example, crosslinking agents and chain transferagents.

[0011] Molecular weight regulators of this type are typically addedto polymerization mixtures in an amount of 0 to 3 wt %. Especiallychain transfer agents frequently constitute a factor which shouldbe reduced in view of the noxiant content of the plastics andundesirable properties.

[0012] It is the shear diversity of influences on the degree ofcrosslinking of a polymer during the polymerization reaction whichmakes regulating the degree of crosslinking in manufacturedelastomers problematic. Not only the reactants influence theproperties, but also the additives, the reaction time, the reactiontemperature and further parameters such as the degree of branching.It therefore appears necessary to provide a process enabling thedegree of crosslinking of an elastomeric component to be determinedand the polymerization process to be adapted thereto in order thusto obtain polymers having optimized properties. A reduction in theamount of chain transfer agents to be admixed should further alsobe obtained.

[0013] It is an object of the present invention to provide aprocess capable of producing a polymer composition having optimizedmechanical properties while employing a low level of chain transferagent. We have found that this object is achieved by the processdescribed hereinafter.

[0014] One subject of the invention is a process for producing athermoplastic polymer composition (A) containing at least onestyrene copolymer (a) and at least one polymeric impact modifier(b) comprising a copolymer (b1) as graft substrate and at least onegraft superstrate (b2) and optionally also further additives (C).The process comprises the steps of: [0015] (1) providing acrosslinked copolymer (b1) by polymerizing a monomer mixturecomprising: [0016] (b11): 70 to 99.99 wt % of at least oneconjugated diene and/or of at least one acrylate, [0017] (b12): 0to 29 wt % of at least one further comonomer selected from:styrene, .alpha.-methylstyrene, acrylonitrile, methacrylonitrile,and methyl methacrylate, [0018] (b13): 0 to 10 wt % of one or morepolyfunctional crosslinking monomers, and [0019] (b14): 0.01 to 0.7wt % of a chain transfer agent, [0020] based on the entire monomerquantity of the polymerization mixture for producing said copolymer(b1); [0021] (2) applying at least one graft superstrate (b2) onsaid copolymer (b1) by polymerizing a monomeric mixture comprising:[0022] (b21): 65 to 95 wt % of at least one vinylaromatic monomer,[0023] (b22): 5 to 35 wt % of acrylonitrile and/ormethacrylonitrile, and [0024] (b23): 0 to 30 wt % of at least onefurther monoethylenically unsaturated monomer selected from: methylmethacrylate (MMA), maleic anhydride (MA) and N-phenylmaleimide(N-PMI), [0025] based on the entire monomer quantity of thepolymerization mixture for producing said graft superstrate (b2),[0026] in the presence of said copolymer (b1) as graft substrate toobtain said impact modifier (b); and [0027] (3) blending the atleast one styrene copolymer (a) and the at least one impactmodifier (b) to obtain said polymer composition (A).

[0028] The invention also provides a process wherein theconcentration of chain transfer agent (b14) is from 0.1 to 0.6 wt%, based on the entire monomer quantity of the polymerizationmixture for producing said copolymer (b1).

[0029] The invention also provides a process wherein said copolymer(b1) is provided by admixing the reaction mixture of thepolymerization reaction with a chain transfer agent (b14) from thegroup comprising mercaptans, phosphinates, bisulfites, terpinolsand dimeric a-methylstyrene and mixtures thereof.

[0030] The invention also provides a process wherein said copolymer(b1) is provided by admixing the reaction mixture of thepolymerization reaction with an additional polyfunctionalcrosslinking monomer (b13) in the form of at least one bifunctionalmonomer having two or more reactive unsaturated groups from thegroup comprising ethylene glycol diacrylate, butanediol diacrylate,hexanediol diacrylate, ethylene glycol dimethacrylate, butanedioldimethacrylate, hexanediol dimethacrylate, divinylbenzene, diallylmaleate, diallyl fumarate, diallyl phthalate, diallyl cyanurate,triallyl cyanurate, tricyclodecenyl acrylate,dihydrodicyclopentadienyl acrylate, diallyl phosphate, allylacrylate, allyl methacrylate (AMA), dicyclopentadienyl acrylate(DCPA) and mixtures thereof.

[0031] The invention further provides a thermoplastic polymercomposition (A) obtained or obtainable by the processdescribed.

[0032] The invention also provides a polymer composition (A) whichcontains a styrene/acrylonitrile copolymer (SAN) as styrenecopolymer (a) and also a butadiene-containing copolymer or anacrylate-containing copolymer as polymeric impact modifier (b).

[0033] The invention further provides the method of using thethermoplastic polymer composition (A) in the manufacture ofmoldings, sheetings or coatings.

[0034] The invention also provides a process for optimizing thedegree of crosslinking (V) of a crosslinked copolymer (b1) as graftsubstrate for a polymeric impact modifier (b) produced from amonomer mixture comprising: [0035] (b11): 70 to 99.99 wt % of atleast one conjugated diene and/or of at least one acrylate, [0036](b12): 0 to 29 wt % of at least one further comonomer selectedfrom: styrene, .alpha.-methylstyrene, acrylonitrile,methacrylonitrile, and methyl methacrylate, [0037] (b13): 0 to 10wt % of one or more polyfunctional crosslinking monomers, and[0038] (b14): 0.01 to 0.7 wt % of a chain transfer agent, based onthe entire monomer quantity of the polymerization mixture forproducing said copolymer (b1);

[0039] wherein the process comprises the steps of: [0040] (i)polymerizing the monomer mixture for producing said copolymer (b1);[0041] (ii) determining via NMR relaxation measurements the degreeof crosslinking (V) of said copolymer (b1) obtained in step (i);[0042] (iii) polymerizing a modified monomer mixture to produce amodified copolymer (b1'), wherein the parameters of thepolymerization reaction are adapted according to said degree ofcrosslinking (V) determined as per step (ii) for said copolymer(b1) and according to the desired degree of crosslinking (V') ofsaid copolymer (b1') as graft substrate; and [0043] (iv) repeatingsaid steps (i) to (iii) as often as necessary until a desireddegree of crosslinking (V') is obtained.

[0044] The invention further provides a process wherein thetransversal relaxation time T2 is used to determine said degree ofcrosslinking (V) of said copolymer (b1).

[0045] The invention also provides a process wherein said degree ofcrosslinking (V) of said copolymer (b1) is determined by using alow-field NMR spectrometer at a field strength ranging from 0.001to 1.5 teslas, preferably from 0.1 to 0.6 tesla.

[0046] The invention also provides a process wherein the step ofproviding said copolymer (b1') according to said degree ofcrosslinking (V) determined in step (ii) for said copolymer (b1)resulting from the first polymerization reaction is carried out byadmixing the reaction mixture of the polymerization mixture as perstep (iii) additionally with a polyfunctional crosslinking monomer(b13) as crosslinking agent and/or a chain transfer agent (b14), orchanging the reaction temperature in the polymerization reaction,or a combination thereof.

[0047] The invention also provides a process wherein the step ofproviding said copolymer (b1') is carried out by subjecting thereaction mixture of the polymerization reaction to a temperaturechange of not less than 10.degree. C.

[0048] The invention also provides a process wherein the reactionmixture has added to it a chain transfer agent in a concentrationof 0.1 to 0.6 wt %, based on the entire monomer quantity of thepolymerization mixture for producing said copolymer (b1').

[0049] The invention further provides the method of using theprocess as claimed in any one of claims 8 to 13 in the manufactureof a copolymer (b1') having an optimized degree of crosslinking(V').

[0050] The thermoplastic polymer composition (A) preferablyconsists of the polymeric components (a) and (b): [0051] (a): 30 to95 wt %, based on the polymer composition (A), of at least onestyrene copolymer (a) having a weight average molar mass Mw of 150000 to 360 000 g/mol, selected from vinylaromatic copolymersselected from the group consisting of: [0052] styrene-acrylonitrilecopolymers, .alpha.-methylstyrene-acrylonitrile copolymers,styrene-maleic anhydride copolymers, styrene-phenylmaleimidecopolymers, styrene-methyl methacrylate copolymers,styrene-acrylonitrile-maleic anhydride copolymers,styrene-acrylonitrile-phenylmaleimide copolymers,.alpha.-methyl-styrene-acrylonitrile-methyl methacrylatecopolymers, .alpha.-methylstyrene-acrylonitrile-t-butylmethacrylate copolymers and styrene-acrylonitrile-t-butylmethacrylate copolymers, [0053] (b): 5 to 70 wt %, based on thepolymer composition (A), of at least one impact modifier (b)consisting of: [0054] (b1): 20-90 wt %, based on the impactmodifier (b), of a copolymer of one or more monomers as graftsubstrate obtained by copolymerizing a monomer mixture comprising:[0055] (b11): 70 to 99.99 wt % of at least one conjugated dieneand/or of at least one acrylate, [0056] (b12): 0 to 29 wt % of atleast one further comonomer selected from: styrene,.alpha.-methylstyrene, acrylonitrile, methacrylonitrile, and methylmethacrylate, [0057] (b13): 0 to 10 wt % of one or morepolyfunctional crosslinking monomers, and [0058] (b14): 0.01 to 0.7wt % of a chain transfer agent, based on the entire monomerquantity of the polymerization mixture for producing said copolymer(b1); [0059] (b2): 10 to 80 wt %, based on the impact modifier (b),of a graft superstrate of one or more monomers consisting of:[0060] (b21): 65 to 95 wt %, preferably 70 to 90 wt %, morepreferably 75 to 85 wt % of at least one vinylaromatic monomer,preferably styrene and/or a-methylstyrene, especially styrene,[0061] (b22): 5 to 35 wt %, preferably 10 to 30 wt %, morepreferably 15 to 25 wt % of acrylonitrile and/or methacrylonitrile,preferably acrylonitrile, and [0062] (b23): 0 to 30 wt %,preferably 0 to 20 wt %, more preferably 0 to 15 wt % of at leastone further monoethylenically unsaturated monomer selected from:MMA, MA and N-PMI, [0063] based on the entire monomer quantity ofthe polymerization mixture for producing said graft superstrate(b2); wherein styrene copolymer (a) and impact modifier (b) sum to100 wt %.

[0064] The viscosity (as measured to ISO 11443) of polymercomposition (A) at shear rates of 1 to 10 s.sup.-1 and attemperatures of 250.degree. C. is preferably not more than1.times.10.sup.5 Pa*s.

[0065] The melt volume rate (MVR, measured to ISO 1133 at220.degree. C. and 10 kg load) is preferably more than 6 ml/10min.

[0066] The weight average molar mass Mw is determined via knownmethods of GPC with UV detection.

[0067] The proportion of thermoplastic polymer composition (A) thatis attributable to polymer (a) and to impact modifier (b) is from40 to 90 wt % and from 60 to 10 wt % respectively.

[0068] More preferably, the proportion of polymer composition (A)that is attributable to polymer (a) and to impact modifier (b) isfrom 50 to 80 wt % and from 50 to 20 wt % respectively. Especiallythe proportion of polymer composition (A) that is attributable topolymer (a) and to impact modifier (b) is from 60 to 75 wt % andfrom 40 to 25 wt % respectively.

[0069] Styrene Copolymer (a)

[0070] The styrene copolymer (a) constitutes a hard phase having aglass transition temperature Tg of >20.degree. C. The weightaverage molar masses Mw of styrene copolymers (a) are typically inthe range from 150 000 to 360 000 g/mol, preferably in the rangefrom 150 000 to 300 000 g/mol, more preferably in the range from150 000 to 270 000 g/mol, yet more preferably in the range from 150000 to 250 000 g/mol and especially in the range from 150 000 to220 000 g/mol.

[0071] Styrene copolymer (a) as used for the purposes of theinvention comprises vinyl-aromatic copolymers selected from thegroup consisting of styrene-acrylonitrile copolymers,.alpha.-methylstyrene-acrylonitrile copolymers, styrene-maleicanhydride copolymers, styrene-phenylmaleimide copolymers,styrene-methyl methacrylate copolymers,styrene-acrylonitrile-maleic anhydride copolymers,styrene-acrylonitrile-phenylmaleimide copolymers,.alpha.-methylstyrene-acrylonitrile-methyl methacrylate copolymers,.alpha.-methylstyrene-acrylonitrile-t-butyl methacrylate copolymersand styrene-acrylonitrile-t-butyl methacrylate copolymers.

[0072] The aforementioned polymers (a) are preferably amorphouspolymers. Particular preference for use as styrene copolymer (a) isgiven to styrene-acrylonitrile copolymers (SAN), styrene-methylmethacrylate copolymers (SMMA), and/or styrene-maleic anhydridecopolymers (SMA). Preference is given to styrene-acrylonitrilecopolymers (SAN).

[0073] SAN copolymers and a-methylstyrene-acrylonitrile copolymers(AMSAN) used as styrene copolymer (a) in the present inventioncontain in general from 18 to 35 wt %, preferably from 20 to 32 wt% and more preferably from 22 to 30 wt % of acrylonitrile (AN) andfrom 82 to 65 wt %, preferably from 80 to 68 wt % and morepreferably from 78 to 70 wt % of styrene (S) or, respectively,.alpha.-methylstyrene (AMS), subject to the proviso that the sumtotal of styrene/a-methylstyrene and acrylonitrile adds up to 100wt %.

[0074] The SAN and AMSAN copolymers used generally have a weightaverage molar mass Mw of 150 000 to 350 000 g/mol, preferably 150000 to 300 000 g/mol, more preferably 150 000 to 250 000 g/mol andmost preferably 150 000 to 200 000 g/mol.

[0075] SMMA copolymers used as styrene copolymer (a) for thepurposes of the present invention contain in general from 18 to 50wt %, preferably from 20 to 30 wt % of methyl methacrylate (MMA)and from 50 to 82 wt %, preferably from 80 to 70 wt % of styrenesubject to the proviso that the sum total of styrene and MMA addsup to 100 wt %.

[0076] SMSA copolymers used as styrene copolymer (a) for thepurposes of the present invention contain in general from 10 to 40wt % and preferably from 20 to 30 wt % of maleic anhydride (MA) andfrom 60 to 90 wt % and preferably from 80 to 70 wt % of styrenesubject to the proviso that the sum total of styrene and MA adds upto 100 wt %.

[0077] The styrene copolymer (a) has a viscosity number VN(determined to DIN 53 726 at 25.degree. C. on a 0.5 wt % solutionof polymer (A) in dimethylformamide) of 50 ml/g to 120 ml/g,preferably 52 ml/g to 100 ml/g and more preferably 55 ml/g to 80ml/g.

[0078] The styrene copolymers (a) are obtained in the known mannerby bulk, solution, suspension, precipitation or emulsionpolymerization, of which bulk polymerization and solutionpolymerization are preferable. Details of these processes aredescribed for example in Kunststoffhandbuch, eds. R. Vieweg and G.Daumiller, volume 4 "Polystyrol", Carl-Hanser-Verlag Munich 1996,p. 104 ff and also in "Modern Styrenic Polymers: Polystyrenes andStyrenic Copolymers" (eds., J. Scheirs, D. Priddy, Wiley,Chichester, UK, (2003), pages 27 to 29) and in GB-A 1472195.

[0079] Useful SAN copolymers include commercially available SANcopolymers such as, for example, Luran.RTM. from Styrolution(Frankfurt). Preference is given to using SAN copolymers having anS/AN ratio (in weight percent) of 81/19 to 67/33 and an MVR(measured to ISO 1133 at 220.degree. C. and 10 kg load) of not lessthan 10 ml/10 min, e.g., Luran 368.

[0080] Polymeric Impact Modifier (b)

[0081] The impact modifier (b) constitutes a soft phase having aglass transition temperature TG of <0.degree. C., preferably<-20.degree. C., more preferably <-40.degree. C.

[0082] The particle size of impact modifiers (b) is generally notless than 50 nm and not more than 8 .mu.m, preferably in the rangefrom 60 nm to 5 .mu.m, more preferably in the range from 80 nm to 3.mu.m and most preferably in the range from 80 nm to 2 .mu.m.Impact modifiers (b) of the present invention are obtainable withbi-, tri- or multimodal particle size distributions.

[0083] The impact modifier (b) in the present invention oftencontains: [0084] (b1): 20 to 90 wt %, preferably 40 to 90 wt %,more preferably 45 to 85 wt % and most preferably 50 to 80 wt % ofa copolymer of one or more monomers as graft substrate obtained bycopolymerizing a monomer mixture comprising: [0085] (b11): 70 to99.99 wt % of at least one conjugated diene and/or of at least oneacrylate, [0086] (b12): 0 to 29 wt % of at least one furthercomonomer selected from: styrene, .alpha.-methylstyrene,acrylonitrile, methacrylonitrile, and methyl methacrylate, [0087](b13): 0 to 10 wt % of one or more polyfunctional crosslinkingmonomers, and [0088] (b14): 0.01 to 0.7 wt % of a chain transferagent, [0089] based on the entire monomer quantity of thepolymerization mixture for producing said copolymer (b1); [0090](b2): 10 to 80 wt %, preferably 10 to 60 wt %, more preferably 15to 55 wt % and most preferably 20 to 50 wt % of a graft superstrateof one or more monomers consisting of: [0091] (b21): 65 to 95 wt %,preferably 70 to 90 wt %, more preferably 75 to 85 wt % of at leastone vinylaromatic monomer, preferably styrene and/or.alpha.-methylstyrene, especially styrene, [0092] (b22): 5 to 35 wt%, preferably 10 to 30 wt %, more preferably 15 to 25 wt % ofacrylonitrile and/or methacrylonitrile, preferably acrylonitrile,and [0093] (b23): 0 to 30 wt %, preferably 0 to 20 wt %, morepreferably 0 to 15 wt % of at least one further monoethylenicallyunsaturated monomer selected from: MMA, MA and N-PMI, preferablyMMA, [0094] based on the entire monomer quantity of thepolymerization mixture for producing said graft superstrate(b2).

[0095] Useful conjugated dienes (b11) include dienes having 4 to 8carbon atoms such as butadiene, isoprene, piperylene andchloroprene or mixtures thereof. Preference is given to usingbutadiene or isoprene or mixtures thereof, most preferablybutadiene.

[0096] Copolymers (b1) based on conjugated dienes (b11) include,for example, copolymers of the aforementioned conjugated dienes(b11) with each or one another, copolymers of such dienes withacrylates (b11), especially n-butyl acrylate, and copolymers ofsuch dienes with the comonomers (b12) selected from styrene,.alpha.-methylstyrene, acrylo-nitrile, methacrylonitrile and methylmethacrylate which were produced in the presence of a chaintransfer agent (b14) in the stated amount.

[0097] The diene polymers may also contain additional crosslinkingpolyfunctional monomers (b13). Examples thereof are monomerscontaining two or more copolymerization-capable double bonds suchas ethylene glycol diacrylate, butanediol diacrylate, hexanedioldiacrylate, ethylene glycol dimethacrylate, butanedioldimethacrylate, hexanediol dimethacrylate, divinylbenzene, diallylmaleate, diallyl fumarate, diallyl phthalate, diallyl cyanurate,trisallyl cyanurate, esters of tricyclodecenyl alcohol such astricyclodecenyl acrylate, dihydrodicyclopentadienyl acrylate,diallyl phosphate, allyl acrylate, allyl methacrylate anddicyclopentadienyl acrylate (DCPA). Preference is given to usingesters of tricyclodecenyl alcohol, divinylbenzene, allyl(meth)acrylate and/or trisallyl cyanurate. Preferred diene polymersare commercially available butadiene, butadiene-styrene,butadiene-methyl methacrylate, butadiene-n-butyl acrylate,butadiene-acrylonitrile and acrylonitrile-butadiene-styrenecopolymers (ABS); particular preference is given to ABScopolymers.

[0098] Such preferred diene copolymers (b1) and ABS impactmodifiers (b) are described in EP 0 993 476.

[0099] Copolymers (b1) based on acrylates are generally alkylacrylate polymers formed from one or more C4-C8 alkyl acrylates,preferably butyl, hexyl, octyl or 2-ethylhexyl acrylate being usedin part at least. These alkyl acrylate copolymers may contain up to29 wt % of monomers such as styrene, .alpha.-methylstyrene,acrylonitrile, methacrylonitrile and methyl methacrylate inpolymerized form which form hard polymers.

[0100] The aforementioned impact modifiers (b) are preferablyacrylonitrile-butadiene-styrene (ABS) and/oracrylonitrile-styrene-acrylate (ASA) copolymers.

[0101] Acrylonitrile-styrene-acrylate copolymers (ASA) are apreferred embodiment. The acrylate copolymers further contain up to10 wt %, preferably from 1 to 5 wt % of crosslinking polyfunctionalmonomers (b13) (crosslinking monomers). Examples thereof aremonomers containing two or more copolymerization-capable doublebonds such as ethylene glycol diacrylate, butanediol diacrylate,hexanediol diacrylate, ethylene glycol dimethacrylate, butanedioldimethacrylate, hexanediol dimethacrylate, divinylbenzene, diallylmaleate, diallyl fumarate, diallyl phthalate, diallyl cyanurate,trisallyl cyanurate, esters of tricyclodecenyl alcohol such astricyclodecenyl acrylate, dihydrodicyclopentadienyl acrylate,diallyl phosphate, allyl acrylate, allyl methacrylate anddicyclopentadienyl acrylate (DCPA). Preference is given to usingesters of tricyclodecenyl alcohol, divinylbenzene, allyl(meth)acrylate and/or trisallyl cyanurate.

[0102] The impact modifier (b) produced according to the inventionis more preferably an ABS impact modifier (b) comprising [0103](b1): 40 to 90 wt %, based on the impact modifier (b), of a graftsubstrate consisting of: [0104] (b11): 70 to 99.99 wt %, preferably90 to 99.89 wt % of butadiene, [0105] (b12): 0 to 29 wt %,preferably 1 to 10 wt % of styrene, and [0106] (b14): 0.01 to 0.7wt % of a chain transfer agent, [0107] based on the entire monomerquantity of the polymerization mixture for producing the copolymer(b1); and [0108] (b2): 10 to 60 wt %, based on the impact modifier(b), of a graft superstrate consisting of: [0109] (b21): 65 to 95wt % of styrene, [0110] (b22): 5 to 35 wt % of acrylonitrile, and[0111] (b23): 0 to 30 wt % of MMA, [0112] based on the entiremonomer quantity of the polymerization mixture for producing thegraft superstrate (b2).

[0113] The soft component is preferably a multistagedly constructedcopolymer having a core-shell construction and a core-shellmorphology. For example, a rubberily elastic core (glass transitiontemperature TG<50.degree. C.) may be enveloped by a "hard" shell(polymers with TG>50.degree. C.), or vice versa. Core-shellgraft copolymers of this type are known.

[0114] Production of Impact Modifiers (b)

[0115] Processes for producing the impact modifiers (b) areconceptually known to the notional person skilled in the art andare described in the literature. Some products of this type arecommercially available. Emulsion polymerization has proved to beparticularly advantageous for the process of production (DE-C 12 60135 and EP 0 993 476 B1). The production of impact modifiers (b)generally comprises producing a copolymer (b1) as graft substrateand producing a graft superstrate (b2).

[0116] Production of Copolymer (b1)

[0117] The polymerization temperature is typically in the rangefrom 20 to 100.degree. C. and preferably in the range from 30 to80.degree. C. Customary emulsifiers are generally also used,examples being alkali metal salts of alkyl- or alkylarylsulfonicacids, alkyl sulfates, fatty alcohol sulfonates, salts of higherfatty acids having 10 to 30 carbon atoms, sulfosuccinates, ethersulfonates or resin soaps. Preference is given to using the alkalimetal salts, especially the sodium and potassium salts, ofalkylsulfonates or fatty acids having 10 to 18 carbon atoms.

[0118] The amounts in which the emulsifiers are used are generallyin the range from 0.5 to 5 wt % and especially in the range from0.5 to 3 wt %, based on the monomers used in the production ofcopolymer (b1).

[0119] The amount of water used for producing the dispersion ispreferably such that the final dispersion has a solids content of20 to 50 wt %. A water/monomer ratio in the range from 2:1 to 0.7:1is typically used.

[0120] The polymerization reaction can be suitably initiated usingany free-radical generators which decompose at the reactiontemperature chosen, i.e., not only those which decompose thermallyon their own but also those which decompose thermally in thepresence of a redox system. The polymerization initiators used arepreferably free-radical generators, for example peroxides such as,preferably, peroxosulfates (sodium persulfate or potassiumpersulfate, say) and azo compounds such as azodiisobutyro-nitrile.However, it is also possible to use redox systems, especially redoxsystems based on hydroperoxides such as cumene hydroperoxide.

[0121] The polymerization initiators are generally used in anamount of 0.1 to 1 wt %, based on the graft substrate monomers(b11) and (b12). The polymerization initiators are preferably usedin an amount of 0.1 to 0.5 wt % based on the entire monomerquantity of the polymerization mixture, especially in an amount of0.2 to 0.4 wt % based on the entire monomer quantity of thepolymerization mixture for producing copolymer (b1).

[0122] The free-radical generators and also the emulsifiers areadded to the reaction batch for example batchwise by adding theoverall quantity at the start of the reaction, or by beingsubdivided into a plurality of portions which are added at thestart and at one or more subsequent junctures, or continuouslyduring a specified time interval.

[0123] The continuous addition process can also follow a gradient,which may for example be upwardly or downwardly inclined, linear orexponential, or else may be a stepped gradient (step function).

[0124] Chain transfer agents are used in a concentration of lessthan 0.75 wt %, especially less than 0.7 wt %, based on the entiremonomer quantity used. The chain transfer agents are preferablyused in an amount ranging from 0.01 to 0.7 wt %, preferably in anamount ranging from 0.1 to 0.6 wt %, especially in an amountranging from 0.2 to 0.6 wt %, based on the entire monomer quantityused for producing copolymer (b1). Particular preference is givento an admixture in an amount ranging from 0.3 to 0.6 wt % andespecially from 0.4 to 0.55 wt %, based on the entire monomerquantity.

[0125] Suitable chain transfer agents include, for example,mercaptans, phosphinates, bisulfites, terpinols and dimerica-methylstyrene, especially mercaptomethanol, ethyl-hexylthioglycolate, n-dodecyl mercaptan, t-dodecyl mercaptan,mercaptopropionic acid, bis-(isopropylxanthogen) disulfite, sodiumhypophosphite (NHP) and mixtures thereof.

[0126] Particular preference is given to using t-dodecyl mercaptanas chain transfer agent in an amount ranging from 0.01 to 0.7 wt %,preferably in an amount ranging from 0.1 to 0.6 wt %, especially inan amount ranging from 0.2 to 0.6 wt %, based on the entire monomerquantity used for producing copolymer (b1). Particular preferenceis given to an admixture of t-dodecyl mercaptan in an amountranging from 0.3 to 0.6 wt % and especially from 0.4 to 0.55 wt %,based on the entire monomer quantity.

[0127] It is further possible to admix additional polyfunctionalcrosslinking monomers as crosslinking agents in an amount of 0 to10 wt %.

[0128] Suitable crosslinking agents include, for example, ethyleneglycol diacrylate, butanediol diacrylate, hexanediol diacrylate,ethylene glycol dimethacrylate, butanediol dimethacrylate,hexanediol dimethacrylate, divinylbenzene, diallyl maleate, diallylfumarate, diallyl phthalate, diallyl cyanurate, trisallylcyanurate, esters of tricyclodecenyl alcohol such astricyclodecenyl acrylate, dihydrodicyclopentadienyl acrylate,diallyl phosphate, allyl acrylate, allyl methacrylate anddicyclopentadienyl acrylate (DCPA) and mixtures thereof. Preferenceis given to using esters of tricyclodecenyl alcohol,divinylbenzene, allyl (meth)acrylate and/or trisallylcyanurate.

[0129] The chain transfer agents and crosslinking agents are addedto the reaction batch in a batchwise or continuous manner asdescribed above for the free-radical generators and emulsifiers.The amount in which and the time at which molecular weightregulators are admixed are preferably chosen according to thedegree of crosslinking desired from the polymerization. Batchwiseadmixture is preferred. For example, admixture is effected in from1 to 7 steps, preferably in from 2 to 5 steps and especially in 3or 4 steps.

[0130] The time of admixture is freely choosable in principle.Preferably, the first admixture of chain transfer agents and/orcrosslinking agents takes place once from about 10 to 20% of theentire reaction time from the start of the polymerization haselapsed, especially once from about 12 to 16% of the reaction timehas elapsed, more preferably once from about 13 to 14% of thereaction time has elapsed.

[0131] The second admixture of chain transfer and/or crosslinkingagents preferably takes place once from about 45 to 55% of theentire reaction time from the start of the polymerization haselapsed, especially once from about 49 to 53% of the reaction timehas elapsed, more preferably once from about 50 to 52% of thereaction time has elapsed. The third admixture of chain transferand/or crosslinking agents preferably takes place once from about90 to 100% of the entire reaction time from the start of thepolymerization has elapsed, especially once from about 95 to 99.5%of the reaction time has elapsed, more preferably once from about97 to 99% of the reaction time has elapsed.

[0132] The polymerization time is in the range from 1 minute to 20hours, especially in the range from 1 hour to 16 hours andpreferably in the range from 4 hours to 12 hours.

[0133] The admixture scheme resulting in the case of an exemplaryoverall reaction time of 8.5 hours is for example as follows: thefirst admixture of chain transfer and/or crosslinking agentspreferably takes place at from 50 to 90 minutes from the start ofthe polymerization, especially after 60 to 80 minutes and morepreferably after 65 to 75 minutes. The second admixture of chaintransfer and/or crosslinking agents preferably takes place at from240 to 280 minutes from the start of the polymerization, especiallyafter 250 to 270 minutes and more preferably after 255 to 265minutes. The third admixture of chain transfer and/or crosslinkingagents preferably takes place at from 480 to 510 minutes from thestart of the polymerization, especially after 490 to 510 minutesand more preferably after 495 to 505 minutes.

[0134] The admixed amount of chain transfer and/or crosslinkingagent in every admixing step may be the same and correspond to auniform proportion of the entire amount admixed. Preferably,however, more chain transfer and/or crosslinking agent is admixedin the first admixing step than in the last admixing step. Forexample, in an admixture scheme of three admixing steps, about 35to 45 wt % of the total quantity of chain transfer and/orcrosslinking agent is admixed in both the first and second admixingsteps, while about 10 to 30 wt % of the total amount of chaintransfer and/or crosslinking agent is admixed in the third admixingstep.

[0135] Buffering substance such asNa.sub.2HPO.sub.4/NaH.sub.2PO.sub.4, sodium bicarbonate or buffersbased on citric acid/citrate may be used to maintain a consistentpH, which is preferably in the range from 6 to 9. Regulators andbuffering substances are used in the customary amounts, so there isno need for more particular indications in this regard.

[0136] In one particular embodiment, copolymer (b1) is alsoobtainable by polymerizing the monomers (b11) to (b13) in thepresence of chain transfer agent (b14) and of a finely dividedlatex (in the so-called "seed latex mode" of the polymerizationprocess).

[0137] This latex is initially charged and may consist of monomersforming rubberily elastic polymers or else of other monomers asalready recited. Suitable seed latices consist, for example, ofpolybutadiene or polystyrene. Seed latices are more preferably ofpolystyrene.

[0138] In another preferred embodiment, copolymer (b1) isobtainable in the so-called feed stream addition process. In thisprocess, a certain proportion of monomers (b11) to (b13) and ofchain transfer agent (b14) is initially charged and thepolymerization is initiated, whereupon the rest of monomers (b11)to (b13) and, as the case may be, of chain transfer agent (b14)(the "feed stream addition portion") is added as a feed streamduring the polymerization.

[0139] The feed stream addition parameters (gradient shape, amount,duration, etc.) depend on the other polymerization conditions.Again, the remarks made regarding the admixture method for thefree-radical starter and/or emulsifier apply here mutatis mutandis.The initially charged proportion of the monomers for producing (b1)in the feed stream addition process is preferably in the range from5 to 50, more preferably 8 to 40 wt %, based on (b1). The feedstream addition portion of (b11) to (b13) is preferably added over1 to 18 hours, especially 2 to 16 hours, more preferably 4 to 12hours.

[0140] The precise conditions for the polymerization, especiallythe type, amount and dosage regime of the emulsifier and of theother polymerization assistants are preferably chosen such that thelatex obtained for impact modifier (b) has an average particlesize, defined by the d50 value of the particle size distribution,in the range from 80 to 1000 nm, preferably in the range from 85 to600 nm and more preferably in the range from 90 to 500 nm.

[0141] The reaction conditions for the polymerization of copolymer(b1) are typically chosen so as to obtain a graft substrate in aspecified crosslinked state. Essential parameters therefor are thereaction temperature and duration, the ratio of monomers,regulators, free-radical initiators and, in the feed streamaddition process for example, the feed stream addition rate and theamount and timing for the admixture of regulator and initiator. Asto the precise procedure, reference is made to the hereinbelowfollowing description of the process for optimizing the degree ofcrosslinking.

[0142] The reaction conditions may be aligned such that the polymerparticles have a bimodal type of particle size distribution, i.e.,a size distribution having two more or less defined maxima. Thefirst maximum is more distinctly defined (as a comparatively narrowpeak) than the second maximum and is generally located at from 25to 200 nm, preferably at from 60 to 170 nm and more preferably atfrom 70 to 150 nm. The second maximum is comparatively broad andgenerally locates at from 150 to 800 nm, more preferably at from180 to 700 nm and more preferably at from 200 to 600 nm. The secondmaximum (150 to 800 nm) is located at larger particle sizes thanthe first maximum (25 to 200 nm).

[0143] The bimodal type of particle size distribution is preferablyachieved via a (partial) agglomeration of the polymer particles. Apossible procedure for this is for example as follows: Monomers(b11) to (b13) are polymerized in the presence of chain transferagent (b14), which construct the core, up to a conversion oftypically not less than 90%, preferably above 95%, based on themonomers used. This conversion is generally reached after 4 to 20hours. The polymer latex obtained has an average particle size d50of not more than 200 nm and a narrow particle size distribution (itis a nearly monodisperse system).

[0144] The polymer latex is agglomerated in the second stage. Thisis generally accomplished by admixing a dispersion of an acrylicester polymer. Preference is given to using dispersions ofcopolymers of C1-C4 alkyl esters of acrylic acid, preferably ofethyl acrylate, with from 0.1 to 10 wt % of monomers forming polarpolymers, e.g., acrylic acid, methacrylic acid, acrylamide,methacrylamide, N-methylolmethacrylamide or N-vinylpyrrolidone. Acopolymer formed from 96% ethyl acrylate and 4% methacrylamide isparticularly preferable. The agglomerating dispersion mayoptionally also contain a plurality of the acrylic ester polymersreferred to.

[0145] The concentration of acrylic ester polymers in thedispersion used for agglomeration shall generally be between 3 and40 wt %.

[0146] Agglomeration utilizes from 0.2 to 20, preferably 1 to 5parts by weight of the agglomerating dispersion per 100 parts ofthe polymer latex, all reckoned on solids. The agglomeration iscarried out by admixing the agglomerating dispersion to thepolymer. The rate of admixing is normally not critical, itgenerally takes about 1 to 30 minutes at a temperature between 20and 90.degree. C., preferably between 30 and 75.degree. C.

[0147] Aside from using an acrylic ester polymer dispersion, thepolymer latex may also be agglomerated with other agglomeratingagents such as, for example, acetic anhydride.

[0148] Agglomeration is also possible by pressure or freezing(making for a pressure agglomeration and a freeze agglomeration,respectively). The methods referred to are known to a personskilled in the art.

[0149] Under the conditions referred to, only a portion of thepolymer particles is agglomerated, resulting in a bimodaldistribution. Following the agglomerating step, generally more than50% and preferably between 75% and 95% of the particles(number-based distribution) is in a nonagglomerated state. Thepartially agglomerated polymer latex obtained is comparativelystable, so it is readily storable and transportable withoutoccurrence of coagulation.

[0150] To obtain a bimodal type of particle size distribution forimpact modifier (b), it is also possible to produce two differentimpact modifiers (b) and (b*), which differ in their averageparticle size, separately from each other in the usual manner andto add the impact modifiers (b) and (b*) together in the desiredmixing ratio.

[0151] Production of Graft Superstrate (b2)

[0152] Graft superstrate (b2) is obtainable under the sameconditions as used for producing copolymer (b1), in which case theproduction process for graft (b2) may be carried out in one or moresteps. In two-stage grafting, for example, initially styrene, forexample, alone and thereafter styrene and acrylonitrile arepolymerizable in two successive steps.

[0153] This two-stage grafting (initially styrene, thenstyrene/acrylonitrile) is a preferred embodiment. Further detailsregarding the production of graft copolymers and/or impactmodifiers (b) are described in German Laid-Open Specifications DOS12 60 135 and 31 49 358.

[0154] It is advantageous for the graft polymerization on copolymer(b1) as graft substrate to be again carried out in aqueousemulsion. The graft polymerization may be carried out in the samesystem as the polymerization of the graft substrate, in which caseemulsifier and initiator may further be admixed. These need not beidentical to the emulsifiers and initiators, respectively, used forproducing copolymer (b1). It may thus for example be advantageousto use a persulfate as initiator for producing copolymer (b1), buta redox initiator system for polymerizing the graft superstrate(b2). Otherwise the choice of emulsifier, initiator andpolymerization assistants is subject to the remarks made inconnection with producing copolymer (b1). The monomer mixture to begrafted onto the substrate may be admixed to the reaction mixtureall at once, batchwise in two or more stages or preferably in acontinuous manner during the polymerization.

[0155] In a particularly preferred embodiment, a reducing agent isadded during the grafting of the copolymer (b1) substrate withmonomers (b21) to (b23).

[0156] Insofar as ungrafted polymers are formed from monomers (b21)to (b23) in the course of the grafting of copolymer (b1), theamounts, which are generally below 10 wt % of (b2), are assigned tothe mass of impact modifier (b).

[0157] In a further preferred embodiment, impact modifier (b) isobtainable by bulk polymerization as described for example in"Modern Styrenic Polymers: Polystyrenes and Styrenic Copolymers"(eds., J. Scheirs, D. Priddy, Wiley, Chichester, UK, (2003), pages29 and 305 ff).

[0158] Process for Optimizing the Degree of Crosslinking

[0159] The process which the invention provides for optimizing thedegree of crosslinking (V) of a crosslinked polymer (b1) as graftsubstrate for a polymeric impact modifier (b) comprises the stepsof: [0160] (i) polymerizing the monomer mixture for producing saidcopolymer (b1); [0161] (ii) determining via NMR relaxationmeasurements the degree of crosslinking (V) of said copolymer (b1)obtained in step (i); [0162] (iii) polymerizing a modified monomermixture to produce a modified copolymer (b1'), wherein theparameters of the polymerization reaction are adapted according tosaid degree of crosslinking (V) determined as per step (ii) forsaid copolymer (b1) and according to the desired degree ofcrosslinking (V') of said copolymer (b1') as graft substrate; and[0163] (iv) repeating said steps (i) to (iii) as often as necessaryuntil a desired degree of crosslinking (V') is obtained.

[0164] Regarding impact modifier (b), copolymer (b1) and graftsuperstrate (b2), the above remarks apply.

[0165] Step (i) of the process comprises producing copolymer (b1)by polymerizing a defined mixture of monomers. The above remarksregarding this polymerization step and the selection and quantityof monomers and also other indications made all apply mutatismutandis.

[0166] Step (ii) of the process relates to determining via NMRrelaxation measurements the degree of crosslinking of saidcopolymer (b1) obtained in step (i).

[0167] Nuclear spin relaxation is described by the longitudinalrelaxation time (spin-lattice relaxation time) T1, whichcharacterizes the return of an excited nuclear spin system tothermal equilibrium, and by the transversal relaxation time(spin-spin relaxation time) T2, which describes for how long afteran NMR excitation a signal is detectable.

[0168] Both the relaxation times depend in a characteristic manneron the local mobility of the molecular surroundings of the nuclearspin which is describable using a correlation time .tau.. Thedependence of the transversal relaxation time of the molecularmobility is monotonal, and hence may be deemed a kind ofqualitative rheometer. The use of the transversal relaxation timeT2 is therefore preferable.

[0169] The greater the crosslinking of a certain network, the lowerits T2 times. Customary T2 times for the subject invention graftsubstrates (b1) are T2 times in the range 2.0 to 7 ms, preferably2.5 to 6.0 ms and more preferably 3.0 to 5.5 ms, as measured onfilmed samples at 140.degree. C.

[0170] NMR spectrometers are useful for measuring the transversalrelaxation times T2. Instruments having field strengths of 0.001 to15 teslas are usable. Preference is given to NMR instruments in thelow-field range with field strengths from 0.001 to 1.5 teslas,especially 0.1 to 0.6 tesla. These instruments are small, robustand inexpensive. Analytically relevant information is derivablefrom the nuclear spin relaxation times and also from the relatedsignal amplitudes. Since the relaxation times are determined byanalyzing the NMR signals in the time domain instead of as with NMRspectroscopy in the frequency domain, this is also known as timedomain NMR (TD-NMR).

[0171] The relaxation time can be measured by testing samples ofcopolymer (b1), samples of impact modifier (b) or samples ofpolymer composition (A). The degree of crosslinking is preferablydetermined on the impact modifier (b) or the polymer composition(A), especially on the impact modifier (b).

[0172] The T2 time is determined by measuring the NMR relaxation ofa dewatered and filmed sample or of a sample in the form of aliquid dispersion of polymer. To measure a filmed sample, forexample, the sample is devolatilized overnight and then for examplevacuum dried at 80.degree. C. for 3 h before being measured with asuitable measuring instrument, for example a minispec from Bruker,at 20.degree. C. to 150.degree. C., preferably at 30.degree. C. to140.degree. C.

[0173] The sample may also be taken directly from the reactionmixture, and measured as a liquid dispersion of polymer, withoutfurther sample preparation.

[0174] Said measurement may utilize what is known as the solid echoCarr-Purcell-Meiboom-Gill sequence (SE-CPMG). Further informationregarding this method is for example found in: N. Nestle, K.Haberle, Analytica Chimica Acta 654 (2009) 35-39. SE-CPMG is amethod where pulsed NMR is used for determining the spin-spinrelaxation time T2. In this method, spin echoes are generated atrelatively short intervals. Time intervals of 80 .mu.s to 200 .mu.sare preferable. Advantages to this approach include, firstly, itsquickness, since the entire transversal magnetization decay is readoff with a single excitation event and, secondly, its relativelylow sensitivity to diffusion effects in liquid phase. In the CPMGmethod, the diffusion-based error is only linearly dependent ontime and minimizable by short intervals between pulses. SE-CPMGexperiments are preferably carried out on liquid dispersions ofgraft substrate (b1) polymer and at 20.degree. C. to 50.degree. C.,especially at 25.degree. C. to 40.degree. C.

[0175] Filmed samples can be investigated using the Hahn echoexperiments and solid state echo experiments known to a personskilled in the art. The Hahn echo experiment (or spin echoexperiment) is carried out using the pulse sequence90.degree.-.tau.-180.degree.-.tau.-echo, where .tau. is the timeinterval between the pulses. In the solid state echo experiment, asequence of two 90.degree. pulses oriented perpendicularly to eachother are used to generate an echo, refocusing the influence of themutual magnetic dipole-dipole interaction of the nuclei in a solidstate body. The NMR measurements on filmed samples are carried outat 20.degree. C. to 150.degree. C., preferably at 30.degree. C. to140.degree. C.

[0176] For samples to be comparable they have to have been preparedand measured by the same method, since the relaxation is distinctlydependent on the measuring conditions, for example the temperature,and the manner of sample preparation.

[0177] The degree of crosslinking (V) of copolymer (b1) ispreferably determined via measurements of the transversalrelaxation times T2.

[0178] The measurements are specifically carried out via low-fieldNMR spectroscopy at field strengths of 0.001 to 1.5 teslas. Fieldstrengths of 0.1 to 0.6 tesla are particularly preferable.

[0179] These can be carried out not only on liquid dispersions ofpolymer but also on solid samples of polymer, for example in theform of polymer films. Especially the SE-CPMG method is thepreferred method of measuring polymer dispersions. Polymer filmsare preferably investigated with a Hahn echo or solid state echoexperiment.

[0180] In the process of the present invention, the degree ofcrosslinking (V) of copolymer (b1) is determined in order thus toadapt the reaction conditions of the polymerization reaction forproducing copolymer (b1) to the desired degree of crosslinking.This is accomplished by a modified monomer mixture beingpolymerized in step (iii) of the process to produce a modifiedcopolymer (b1'). This modified monomer mixture differs from thefirst monomer mixture in that the composition is varied. Moreparticularly, the amounts of additional crosslinking monomer (b13)and of chain transfer agent (b14) are varied.

[0181] Further, the parameters of the polymerization reaction areadapted according to said degree of crosslinking (V) determined asper step (ii) for said copolymer (b1) and according to the desireddegree of crosslinking (V') of said copolymer (b1') as graftsubstrate. This may be accomplished by changing the reactiontemperature and duration, the ratio of monomers, regulators andfree-radical initiators and, in the feed stream addition processfor example, by changing the feed stream addition rate and theamount and timing for admixture of regulator and initiator. Moreparticularly, the reaction is controlled by the admixture ofcrosslinking agents or chain transfer agents.

[0182] Crosslinking agents for controlling the degree ofcrosslinking in the present invention are the polyfunctionalmonomers (b13) (crosslinking monomers). Examples thereof aremonomers containing two or more copolymerization-capable doublebonds such as ethylene glycol diacrylate, butanediol diacrylate,hexanediol diacrylate, ethylene glycol dimethacrylate, butanedioldimethacrylate, hexanediol dimethacrylate, divinylbenzene, diallylmaleate, diallyl fumarate, diallyl phthalate, diallyl cyanurate,trisallyl cyanurate, esters of tricyclodecenyl alcohol such astricyclodecenyl acrylate, dihydrodicyclopentadienyl acrylate,diallyl phosphate, allyl acrylate, allyl methacrylate anddicyclopentadienyl acrylate (DCPA).

[0183] Preference is given to using esters of tricyclodecenylalcohol, divinylbenzene, allyl (meth)acrylate and/or trisallylcyanurate.

[0184] These are suitable in particular for controlling the degreeof crosslinking of acrylic polymers, especially ofacrylonitrile-styrene-acrylate copolymers (ASA).

[0185] Chain transfer agents in accordance with the presentinvention include, for example, ethylhexyl thioglycolate, n-dodecylmercaptan, tert-dodecyl mercaptan or other mercaptans, terpinolsand dimeric a-methylstyrene and other compounds suitable forregulating the molecular weight. Ethylhexyl thioglycolate,n-dodecyl mercaptan and t-dodecyl mercaptan are particularlysuitable. They are suitable in particular for controlling thedegree of crosslinking of diene polymers, especially ofacrylonitrile-butadiene-styrene copolymers (ABS).

[0186] The invention also provides a process wherein the step ofproviding said copolymer (b1') according to said degree ofcrosslinking determined in step (ii) for said copolymer (b1)resulting from the first polymerization reaction is carried out byadmixing the reaction mixture of the polymerization mixture as perstep (iii) additionally with a polyfunctional crosslinking monomer(b13) as crosslinking agent and/or a chain transfer agent (b14), orchanging the reaction temperature in the polymerization reaction,or a combination thereof.

[0187] The temperature change here preferably amounts to not lessthan 10.degree. C., especially not less than 15.degree. C.

[0188] The admixture of crosslinking agent (b13) and/or of chaintransfer agent (b14) can be effected alone or in combination witheach other. Suitable crosslinking agents (b13) and chain transferagent (b14) are those referred to above.

[0189] The invention also provides a process wherein, in step(iii), the reaction mixture has added to it a chain transfer agentin a concentration of 0.1 to 0.6 wt %, based on the entire monomerquantity of the polymerization mixture for producing said copolymer(b1').

[0190] Following this second polymerization as per step (iii), thedegree of crosslinking (V) of copolymer (b1') obtained in step (ii)is determined. This may again be investigated on samples ofcopolymer (b1'), samples of impact modifier (b') containing thiscopolymer (b1'), or samples of polymer composition (A') producedtherefrom. The degree of crosslinking is preferred on the impactmodifier (b') or the polymer composition (A'), especially on theimpact modifier (b'). The measurement is carried out as describedabove.

[0191] When the results of the investigation show that theresultant degree of crosslinking (V) does not correspond to thedesired degree of crosslinking (V'), steps (i) to (iii) arerepeated as often as desired until a desired degree of crosslinking(V') is obtained.

[0192] Production of Polymer Composition (A)

[0193] Polymer composition (A) according to the present inventionis obtainable from components (a) and (b) by any known method. Thepolymer composition (A) may optionally be admixed with additives(C). These are more particularly described hereinbelow. The polymercomposition is produced in detail as follows:

[0194] The impact modifiers (b) having an optimized degree ofcrosslinking are produced by the process described, preferably viaemulsion polymerization. The degree of crosslinking, as alreadydescribed, is established by suitable measures. The preference hereis for determining the degree of crosslinking (V) by measuring thetransversal relaxation time T2 in low-field NMR experiments and forregulating the degree of crosslinking by the admixture of chaintransfer agents. Other suitable measures familiar to a personskilled in the art may also be taken instead or in combination inorder to establish the degree of crosslinking.

[0195] The resulting dispersion of impact modifiers (b) may eitherbe mixed directly with components (a) and optionally (C), or workedup beforehand.

[0196] The workup of the dispersion of impact modifiers (b) iseffected in a conventional manner. Typically, the first step is toprecipitate the impact modifier (b) out of the dispersion, forexample by admixture of precipitatingly effective salt solutions(such as calcium chloride, magnesium sulfate, alum) or acids (suchas acetic acid, hydrochloric acid or sulfuric acid) or else byfreezing (freeze coagulation). The aqueous phase may be separatedoff in a conventional manner, as for instance by sieving,filtration, decantation or centrifugation. This prior removal ofthe dispersion water yields water-moist impact modifiers (b) havinga residual water content of up to 60 wt %, based on (b), whereinthe residual water may be for example not only externally adherenton impact modifier (b) but also encapsulated therein.

[0197] The impact modifier (b) may thereafter if necessary befurther dried in a known manner, for example with hot air or via astream dryer. It is similarly possible to work up the dispersion byspray drying. The impact modifiers (b) are mixed with the styrenecopolymer (a) and, if present, the further additives (C) in amixing apparatus to form an essentially molten polymercomposition.

[0198] "Essentially molten" is to be understood as meaning that thepolymer composition in addition to the predominant, molten(softened) fraction may further contain a certain proportion ofsolid constituents, for example unmelted filling and reinforcingmaterials such as glass fibers, metal flakes, or else unmeltedpigments, dyes, etc. "Molten" is to be understood as meaning thatthe polymer composition is at least viscid, i.e., at least softenedto the point of being plastically deformable.

[0199] Mixing apparatus used is known to a person skilled in theart. Conjoint extrusion, kneading or rolling are examples ofpossible ways to mix components (a) and (b) and, --if present--(C),for which the aforementioned components have, if necessary, firstbeen isolated from the as-polymerized solution or from the aqueousdispersion.

[0200] When one or more components are incorporated in the form ofan aqueous dispersion or in the form of an aqueous or nonaqueoussolution, the water or, respectively, the solvent is removed fromthe mixing apparatus, preferably an extruder, via a devolatilizingunit.

[0201] Suitable mixing apparatus for carrying out the processincludes, for example, heated batch-operated internal mixers withor without ram, continuous kneaders such as, for example,continuous internal mixers, screw kneaders with axially oscillatingscrews, Banbury mixers, further extruders and also roll mills,heated mixing rolls, and calenders.

[0202] An extruder is preferred for use as the mixing apparatus.Single- or twin-screw extruders for example are particularly usefulfor melt extrusion. A twin-screw extruder is preferable.

[0203] In some cases, the mechanical energy imported by the mixingapparatus during the mixing process is in itself sufficient tocause the mixture to melt, so there is no need to heat the mixingapparatus. Otherwise, the mixing apparatus is generally heated. Thetemperature depends on the chemical and physical properties ofcomponents (a) and (b) and--if present--(C), and must be chosen soas to obtain an essentially molten polymer composition. On theother hand, the temperature must not be unnecessarily high, toavoid thermal injury to the polymer composition. However, themechanical energy imported may also be high enough for the mixingapparatus to possibly even require cooling. The mixing apparatus istypically operated at 160 to 400, preferably 180 to 300.degree.C.

[0204] A preferred embodiment comprises mixing the impact modifier(b) with the styrene copolymer (a) and, if present, the furthercomponent (C) in an extruder, the dispersion of impact modifier (b)being metered into the extruder directly without prior removal ofthe dispersion water. The water is typically removed along theextruder via suitable devolatilizing devices. Useful devolatilizingdevices include, for example, devolatilizing openings providedretention screws (to prevent the polymer composition fromescaping).

[0205] Another, similarly preferred embodiment comprises mixing theaforementioned components in an extruder while the impact modifier(b) is separated beforehand from the dispersion water. This priorremoval of the dispersion water yields water-moist impact modifiers(b) having a residual water content of up to 60 wt %, based on (b).The residual water present may then, as described above, be removedas vapor via devolatilizing means of the extruder.

[0206] It is particularly preferred, however, not to remove theresidual water in the extruder solely as vapor; instead some of theresidual water is mechanically removed in the extruder and leavesthe extruder in liquid phase. In this so-called squeeze process (EP0 993 476 B1, pages 13-16), one and the same extruder is suppliedwith the polymer composition (A) and--if present--the component(C), so the final polymer composition (A) is extruded as theproduct of the process.

[0207] The subject invention polymer composition (A) has a residualmonomer content of not more than 2000 ppm, preferably not more than1000 ppm, more preferably not more than 500 ppm. Residual monomercontent refers to the proportion of the polymer composition that isattributable to unconverted (unpolymerized) monomer.

[0208] The subject invention polymer composition (A) further has asolvent content of, for example, ethylbenzene, toluene, etc. at notmore than 1000 ppm, preferably not more than 500 ppm, morepreferably not more than 200 ppm.

[0209] 10

[0210] The low solvent and residual monomer content is obtainableby employing customary processes for reducing solvents and residualmonomers out of polymer melts, as described for example inKunststoffhandbuch, eds. R. Vieweg and G. Daumiller, volume 4"Polystyrol", Carl-Hanser-Verlag Munich (1996), pages 121 to 139.These processes utilize typical devolatilization apparatus such as,for example, partial vaporizers, flat evaporators, stranddevolatilizers, thin film evaporators, devolatilization extruders,etc.

[0211] Polymer composition (A) further contains not more than 500ppm, preferably not more than 400 ppm and more preferably not morethan 300 ppm of transition metals such as, for example, Fe, Mn andZn.

[0212] Polymer compositions (A) having such a low transition metalcontent are obtainable for example by initiating the polymerizationof the polymers present in the polymer composition by employingredox initiators, but using these redox initiators in minimalamounts in combination with peroxides. Polymer composition (A)should therefore further contain but minimal amounts of transitionmetal-containing minerals (e.g., pigments).

[0213] The viscosity of the entire polymer composition (A) at shearrates of 1 to 10 s.sup.-1 and at temperatures of 250.degree. C. isnot more than 1.times.10.sup.5 Pa*s, preferably not more than1.times.10.sup.4 Pa*s and more preferably not more than1.times.10.sup.3 Pa*s.

[0214] The melt volume rate (MVR, measured to ISO 1133 at220.degree. C. and 10 kg load) is generally more than 6 ml/10 min,preferably more than 8 ml/10 min and more preferably more than 12ml/10 min.

[0215] Polymer composition (A) is very useful in the manufacture ofthermoplastic molding compounds that are further processable intomoldings, sheetings or coatings. A polymer composition (A) used forthis purpose optionally has further added to it one or more furtherpolymers (B) and optionally additives (C).

[0216] The proportion of the molding compound that is attributableto polymer composition (A) is generally in the range from 40 to 100wt %, preferably in the range from 70 to 100 wt % and mostpreferably in the range from 80 to 100 wt %, based on the entiremolding compound.

[0217] The molding compound may optionally further contain at leastone further polymer (B) (other than (A)) selected from the group:polycarbonates, polyamides, poly(meth)-acrylates, polyesters andvinylaromatic-diene copolymers (SBCs). Preference for use aspolymer (B) is given to polycarbonates, polyamides and/orpoly(meth)acrylates. The proportion of polymer (B) is generally inthe range from 0 to 60 wt %, preferably in the range from 0 to 30wt % and more preferably in the range from 0 to 20 wt %, based onthe entire molding compound. Polymer (B), if at all, is typicallypresent in the molding compound at a minimum fraction of 0.1 wt%.

[0218] The molding compound may optionally further containcustomary additives (C), such as stabilizers, antioxidants, agentsagainst thermal decomposition and decomposition by ultravioletlight, lubricating and demolding agents, colorants such as dyes andpigments, fibrous and pulverulent filling and reinforcing agents,nucleating agents, plasticizers, etc. The proportion of additives(C) is generally in the range from 0 to 50 wt %, preferably in therange from 0 to 30, often 0.1 to 30, more preferably 0.2 to 10 wt%, based on the entire molding compound.

[0219] Additives (C), if at all, are typically present in themolding compound at a minimum fraction of 0.1 wt %. The sum totalof components (A) and optionally (B) and/or (C) present in theentire molding compound adds up to 100 wt %. A molding compound ofthe present invention preferably does contain components (A), (B)and (C) or consist thereof.

[0220] When the molding compound contains minerals such as fibrousand pulverulent filling and reinforcing agents and/or pigments asadditive (C) in but minimal amounts, if at all (i.e., at from 0 to5 wt %, based on the entire molding compound), the proportions ofpolymer composition (A) that are attributable to polymer (a) andimpact modifier (b) are preferably in the range from 70 to 95 wt %and from 5 to 30 wt %, respectively.

[0221] The molding compound used further preferably containsessentially amorphous polymers, i.e., at least half the polymerspresent in the molding compound are amorphous polymers.

[0222] The invention is more particularly elucidated by thefollowing examples and claims:

EXAMPLES

[0223] First, the test methods used to characterize the polymersare briefly summarized:

[0224] a) Rubber Content

[0225] The rubber content of the copolymers obtained was determinedvia IR spectroscopy. To this end, the final rubber content iscomputed from the measured ratio of butadiene to styrene toacrylonitrile (each in polymeric form). To this end, a film about20 .mu.m in layer thickness is prepared in a press at 180.degree.C. and measured IR spectroscopically in transmission. Theabsorptions of the bands at 910 cm.sup.-1 and 965 cm.sup.-1 for the1,2-vinyl and 1,4-trans-polybutadiene units, the absorption of theband at 2238 cm.sup.-1 for the nitrile group of the polymerizedacrylonitrile and the absorption of the band at 1495 cm.sup.-1 forthe phenyl group of the polymerized styrene are enlisted to computethe ratio by using a calibration with samples of knowncomposition.

[0226] b) Charpy Notched Impact Strength [kJ/m.sup.2]:

[0227] The notched impact strength is determined to ISO 179-1A at23.degree. C. on sample pieces (80.times.10.times.4 mm, prepared byinjection molding at a melt temperature of 240.degree. C. and amold temperature of 70.degree. C.).

[0228] c) Flowability (MVR [ml/10 min]):

[0229] The flowability is determined to ISO 1133 on a polymer meltat 220.degree. C. and 10 kg loading.

[0230] d) Surface Gloss

[0231] To determine surface gloss, an injection molding machine isused at a melt temperature of 240.degree. C. and a mold temperatureof 70.degree. C. to produce rectangular plaques on the polymer meltwhich measure 60 mm.times.40 mm.times.2 mm. The surface gloss ismeasured by reflection measurement to DIN 67530 at an angle of20.degree..

[0232] e) Yellowness Index YI

[0233] The Y1 value was determined on plaques measuring60.times.40.times.2 mm, prepared by injection molding at a melttemperature of 240.degree. C. and a mold temperature of 70.degree.C., using ASTM method E313-96 (illuminant/observercombination)(C)/2.degree.).

Example 1

[0234] Production of copolymer (b1) in the manner of the presentinvention

[0235] Copolymer (b1) is produced by emulsion polymerizationaccording to the feed stream addition process. Butadiene is used asmonomer, and 7 wt % of styrene as comonomer. The emulsionpolymerization is carried out in a 150 L reactor at a temperatureof 67.degree. C. 43 120 g of the monomer mixture (butadiene andstyrene) are polymerized at 67.degree. C. in the presence of 229.8g (0.533 part based on the entire monomer quantity) of tert-dodecylmercaptan (TDM), 320.8 g of potassium stearate, 106.1 g ofpotassium persulfate, 151.4 g of sodium dicarbonate and 58 400 g ofwater to obtain a latex of the graft substrate at a 42.1 wt %solids content.

[0236] The monomers are introduced into the reactor in thefollowing sequence:

[0237] Styrene is admixed first in an amount of 7 wt %, based onthe entire monomer quantity, in the course of 20 minutes. Thestyrene admixture is followed by the admixture of 0.527 wt % ofstyrene and 6.473 wt % of butadiene, based on the entire monomerquantity, in the course of 25 minutes.

[0238] The rest of the monomers, which corresponds to 86 wt %,based on the entire monomer quantity, and consists of 6.473 wt % ofstyrene and 79.527 wt % of butadiene, is subsequently admixed inthe course of 8.5 hours. TDM is injected at 71 minutes (41.7% oftotal TDM), at 260 minutes (41.7% of the total) and at 500 minutes(16.6% of total TDM). The conversion at the end of thepolymerization time is 95%.

[0239] Determination of the Degree of Crosslinking

[0240] The copolymer latices produced according to the inventionare sampled in various test series. The samples are air driedovernight and vacuum redried at 80.degree. C. for 3 hours to obtainfilmed samples. These are examined at 30.degree. C. and 140.degree.C. by a standard method using solid state echo and Hahn echo. Therelaxation times measured range from 1.28 ms to 1.72 ms for T2(30.degree. C.) and from 3.96 ms to 5.00 ms for T2 (140.degree.C.). The degree of crosslinking is determined from the T2relaxation times measured.

[0241] Production of Impact Modifier (b)

[0242] General Procedure:

[0243] First, 59 parts by weight of graft substrate (b1) latex,based on the solids content of the latex, are initially charged ata temperature of 68.degree. C. and stirred. 1.357 parts by weightof a latex (based on latex solids) of an agglomeratingly effectivecopolymer formed from 96 wt % of ethyl acrylate and 4 wt % ofmethacrylamide are adjusted to 10 wt % with demineralizedwater.

[0244] This dilute latex is admixed to graft substrate (b1) underagitation in the course of 25 minutes for agglomeration. After 5minutes, 0.56 part by weight of potassium stearate, dissolved in40.98 parts by weight of demineralized water at 68.degree. C., isadded to the latex of graft substrate (b1) under continuedagitation.

[0245] On completion of the agglomerating step, 0.074 part byweight of potassium persulfate, dissolved in 3.13 parts by weightof demineralized water, is added to the agglomerated latex of graftsubstrate (b1) at 68.degree. C. under continued agitation. Amonomer mixture of 32.8 parts by weight of styrene and 8.2 parts byweight of acrylonitrile is admixed in the course of 2 hours and 44minutes under continued agitation. In the course of this period ofadding the styrene-acrylonitrile mixture, the temperature is raisedto 80.degree. C. On completion of the addition of thestyrene-acrylonitrile mixture, 0.074 part by weight of potassiumpersulfate dissolved in 3.13 parts by weight of demineralized wateris added under continued agitation. The polymerization is continuedfor 80 minutes at 80.degree. C. and the resultant latex of graftcopolymer (b) is cooled down to ambient temperature.

[0246] The graft latex obtained is admixed with 0.37 part by weightof a dispersion of a stabilizer (based on dispersion solids, thedispersion having a solids content of 60 wt %). Thereafter, thedispersion of the graft copolymer is precipitated with an aqueoussolution of a precipitant in a steam-heated stirred precipitationtank at 4 bar and a temperature of 88.degree. C. This is done byinitially charging the aqueous solution of the precipitant to thesteam-heated precipitation tank and gradually metering in thedispersion of the graft copolymer under agitation once atemperature of 88.degree. C. is reached.

[0247] Thereafter, the precipitation suspension is transferred intoa steam-heated stirred sintering tank. Sintering is effected at 4bar and 116.degree. C. for 60 minutes. Subsequently, the sinteredgraft copolymer is spun in a centrifuge and washed twice with 550parts by weight of demineralized water. The polymer thus worked upis further processed via extrusion at a residual moisture contentof 15 to 30%.

Comparative Example 1

[0248] Production of Comparative Copolymer (V-b1) by ConventionalProcess

[0249] Comparative copolymer (V-b1) is produced by emulsionpolymerization in the feed stream addition process as described inExample 1. The difference is that 345.4 g (0.801 part based onentire monomer quantity) are used of tert-dodecyl mercaptan(TDM).

[0250] Production of Comparative Impact Modifier (V-b)

[0251] Comparative impact modifier (V-b) was produced according tothe protocol for producing invention impact modifier (b) exceptthat comparative impact modifier (V-b1) was used as graftsubstrate.

Example 2

[0252] Production of Polymer Composition (A) from SAN Copolymer (a)and Impact Modifier (b)

[0253] Impact modifier (b) was used to produce polymer compositions(A1) to (A5). To this end, impact modifier (b) is mixed in atwin-screw extruder having a screw diameter of 25 mm with styrenecopolymer (a) in the proportions (based on the entire polymercomposition) reported in table 1 by addition of 1 wt % of thehereinbelow described stabilizer masterbatch. The temperature inthe extrusion zone is set at 200 to 250.degree. C. and theprocessing speed of the twin-screw extruder was 700 rpm. The batchsize is 4 kg for all examples.

[0254] The styrene copolymer chosen as styrene copolymer (a) is arandom copolymer formed from styrene and acrylonitrile (an SANcopolymer) and having an acrylonitrile content of 24 wt %, an Mw of120 000 g/mol, a viscosity number of 64 ml/g (concentration 5 g/lin dimethylformamide measured at 20.degree. C.) and an MVR meltvolume rate of 64 ml/10 min, measured to ISO 1133 at 220.degree. C.and 10 kg loading.

[0255] The stabilizer masterbatch is a masterbatch featuringthermal and light stabilizers such as, for example, Tinuvin 770,Cyasorb 3853, Chimasorb 944 in SAN polymer (Luran VLN).

TABLE-US-00001 TABLE 1 Polymer Amount used of Amount used of Amountused composition impact modifier SAN polymer of stabilizer (A) (b)in wt % (a) in wt % masterbatch in wt % A1 29 80 1 A2 31 78 1 A3 3376 1 A4 35 74 1 A5 37 72 1

[0256] The ABS compositions obtained were tested to determine theirCharpy notched impact strength, flowability (MVR), yellowness index(YI) and surface gloss. This was done using the test methodsdescribed above.

[0257] The rubber content of the samples was determined byperforming the IR measurements described at the beginning on thegranular materials obtained.

[0258] Table 2 summarizes the test results of the ABS compositionstested.

Comparative Example 2

[0259] Comparative polymer compositions V-A1 to V-A5 solely differfrom invention polymer compositions A1 to A5 in that comparativeimpact modifier (V-b) is used for producing the comparative moldingcompounds.

[0260] The ABS compositions obtained were tested to determine theirCharpy notched impact strength, flowability (MVR), yellowness index(YI) and surface gloss. This was done using the test methodsdescribed above.

[0261] The rubber content of the samples was determined byperforming the IR measurements described at the beginning on thegranular materials obtained.

[0262] Table 2 summarizes the test results of the ABS compositionstested.

TABLE-US-00002 TABLE 2 Rubber content Charpy MVR Yellowness Surfacegloss [%] [kJ/m.sup.2] [ml/10 min] Index at 20.degree. V-A1 30.0 1116.5 34.58 97.3 V-A2 31.4 12.8 15.3 34.74 94.1 V-A3 33.0 15.4 13.135.82 92 V-A4 35.6 18.3 11.2 34.89 92.8 V-A5 36.2 20.7 9.2 36.792.1 A1 27.4 11.6 21 34.2 95.8 A2 29.2 14 17.6 35.8 94.4 A3 32.216.5 16.5 36.7 94.8 A4 32.8 17.6 14 37.1 95.1 A5 33.8 21 11.6 36.594.1

[0263] The results show that polymer compositions produced by theprocess of the invention have distinctly better mechanicalproperties. This is attributable to the improved crosslinking ofthe rubber component, this improved crosslinking being the resultof the present process, which makes it possible to reduce theamount of chain transfer agent used. The process of the inventionhas no noticeable adverse effects on the other polymer propertiesreferred to.

[0264] The process of the invention provides improved properties ofimpact modified polymer compositions while at the same timereducing the addition of costly and potentially harmful and/orenvironmentally damaging substances to the polymer composition.

Example 3

[0265] 80% of polymer composition Al is mixed with 20% ofpolycarbonate (based on bisphenol A) in a twin-screw extruderhaving a screw diameter of 25 mm. The temperature in the extrusionzone is set at 200 to 250.degree. C. and the processing speed ofthe twin-screw extruder was 700 rpm. The polymer blend is used toproduce a shaped article.

* * * * *

Process For Producing Thermoplastic Polymer Compositions With Optimized Degree Of Crosslinking Patent Application (2024)
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