Elastic-thermoplastic graft polymers prepared by multi-stage...

Details Elastic-thermoplastic graft polymers prepared by multi-stage... Elastic-thermoplastic graft polymers prepared by multi-stage...

2001-09-28

2003-05-27

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S316000, C525S069000, C525S263000

Reexamination Certificate

active

06569951

ABSTRACT:

CROSS REFERENCE TO RELATED PATENT APPLICATION
The present patent application claims the right of priority under 35 U.S.C. 119 (a)-(d) of German Patent Application No. 100 49 467.6, filed Oct. 6, 2000.
FIELD OF THE INVENTION
The invention provides improved elastic-thermoplastic graft polymers which are obtained by emulsion polymerization adhering to specific reaction conditions during the addition of compounds which regulate the molecular weight. The present invention also relates to thermoplastic compositions and shaped articles comprising the elastic-thermoplastic graft polymers, and a process for the preparation of the elastic-thermoplastic graft polymers.
BACKGROUND OF THE INVENTION
The preparation of elastic-thermoplastic graft polymers, e.g. of graft rubbers from vinyl monomers and rubbers, by emulsion polymerization is known and is described in numerous patent specifications, e.g., EP-A 154 244.
One or more compounds which regulate the molecular weight are often added during the grafting polymerization reaction to improve the graft polymer properties in respect of more favorable processing conditions of thermoplastic molding compositions prepared therefrom.
The disadvantages of graft polymers prepared by such known polymerization methods include, the high costs of the compounds which regulate the molecular weight, and the less than optimum incorporation properties of these molecular weight regulating components.
SUMMARY OF THE INVENTION
There was therefore the object of providing elastic-thermoplastic graft polymers for the preparation of thermoplastic molding compositions, in which the compound which regulates the molecular weight has an optimum activity at a very high incorporation rate when a given amount is employed.
In accordance with the present invention, there is provided an elastic-thermoplastic graft polymer prepared by a multi-stage free radical polymerization of (i) one or more monomers containing vinyl groups, and (ii) at least one molecular weight regulating compound, in the presence of (iii) at least one rubber in latex form, wherein,
in a first reaction stage of the polymerization, the ratio of monomers to the molecular weight regulating compound is from 50:1 to 400:1;
in a second reaction stage of the polymerization, the ratio of monomers to the molecular weight regulating compound is from 100:1 to 800:1;
in a third reaction stage of the polymerization, the ratio of monomers to the molecular weight regulating compound is from 200:1 to 2000:1; and
in at least one further reaction stage of the polymerization, the monomers, in the absence of the molecular weight regulating compound, are polymerized in the presence of the rubber, said further reaction stage occurring at a point selected from at least one of before the first stage and after the third stage,
provided that the ratio of monomers to the molecular weight regulating compound in the first stage is less than or equal to the ratio of monomers to the molecular weight regulating compound in the second stage, and the ratio of monomers to the molecular weight regulating compound in the second stage is less than the ratio of monomers to the molecular weight regulating compound in the third stage.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be under stood as modified in all instance by the term “about.”
DETAILED DESCRIPTION OF THE INVENTION
The duration of the three successive reaction sections here is preferably 10 to 80%, particularly preferably 15 to 70% and very particularly preferably 20 to 60% (first reaction section), preferably 5 to 60%, particularly preferably 10 to 50% and very particularly preferably 15 to 40% (second reaction section), and preferably 10 to 50%, particularly preferably 15 to 45% and very particularly preferably 20 to 40% (third reaction section) (in each case based on the total reaction time of the three reaction sections). The duration of the reaction section without addition of compounds which regulate the molecular weight at the beginning and/or at the end of the grafting polymerization reaction is preferably 5 to 50%, particularly preferably 10 to 45% and very particularly preferably 15 to 40% (based on the total reaction time of the grafting polymerization).
Compared with the elastic-thermoplastic graft polymers known to date, the polymers according to the invention are distinguished by an improved processability and a higher toughness of the rubber-modified thermoplastic molding compositions based thereon, e.g. of the ABS type.
Suitable rubbers used in the preparation of the elastic-thermoplastic graft polymers according to the invention are selected from those rubber-like polymers present in emulsion form which have a glass transition temperature below 0° C.
Classes of preferred rubbers which may be used in the preparation of the elastic-thermoplastic graft polymers according to the invention include diene rubbers and/or acrylate rubbers.
As used herein the term “diene rubbers” refers to homopolymers of conjugated dienes having 4 to 8 C atoms, such as butadiene, isoprene or chloroprene, or copolymers thereof with up to 60 wt. %, preferably up to 30 wt. %, of a vinyl monomer. Examples of vinyl monomers include, but are not limited to acrylonitrile, methacrylonitrile, styrene, &agr;-methylstyrene, halogenostyrenes, C
1
-C
4
-alkylstyrenes, C
1
-C
8
-alkyl acrylates, C
1
-C
8
-alkyl methacrylates, alkylene glycol diacrylates, alkylene glycol dimethacrylates and divinylbenzene.
Acrylate rubbers that may be used include homo- and copolymers of C
1
-C
10
-alkyl acrylates, e.g. and preferably homopolymers of ethyl acrylate or butyl acrylate or copolymers with up to 40 wt. %, preferably not more than 10 wt. %, of vinyl monomers, e.g. and preferably styrene, acrylonitrile, vinyl butyl ether, acrylic acid (esters), methacrylic acid (esters) or vinylsulfonic acid. Those acrylate rubber homo- or copolymers which comprise 0.01 to 8 wt. % of divinyl or polyvinyl compounds and/or N-methylolacrylamide or N-methylolmethacrylamide or other compounds which act as crosslinking agents, e.g., divinylbenzene or triallyl cyanurate, are preferably employed.
Preferred rubbers include polybutadiene rubbers, SBR rubbers with up to 30 wt. % of polymerized-in styrene or acrylate rubbers, in particular those which have a core-shell structure, e.g., as described in DE-A 3 006 804, or mixtures of the rubbers mentioned.
Latices with average particle diameters (d
50
) of 0.05 to 2 &mgr;m, preferably 0.08 to 1 &mgr;m and particularly preferably 0.1 to 0.5 &mgr;m, may be used in the preparation of the graft polymers according to the invention. The gel contents of the rubbers employed can be varied within wide limits, and are preferably between 30 and 95 wt. %. The gel contents being determined by means of a wire cage method in toluene as described in, for example, Houben-Weyl, Methoden der Organischen Chemie, Makromolekulare Stoffe, part 1, p.307 (1961), Thieme Verlag Stuttgart.
Mixtures of rubber latices (or latexes) having different d
50
values are particularly preferred. In an embodiment of the present invention, a mixture of rubber latices (a) and (b) are used. Rubber latex (a) has average particle diameters d
50
of ≦320 nm, preferably 260 to 310 nm, and gel contents of ≦70 wt. %, preferably 40 to 65 wt. %. Rubber latex (b) has average particle diameters d
50
of ≧370 nm, preferably 380 to 450 nm, and gel contents of ≧70 wt. %, preferably 75 to 90 wt. %.
Preferably, the particle size distribution range of rubber latex (a) is 30 to 100 nm, particularly preferably 40 to 80 nm, and that of rubber latex (b) is 50 to 500 nm, particularly preferably 100 to 400 nm (in each case measured as the d
90
-d
10
value from the integral particle size distribution). The average particle diameters are determined by means of an ultracentrifuge, as described in, for example, cf. W. Scholtan, H. Lange: Kolloid-Z. u Z. Polymer 250, p. 782-796 (1972).
The mixtures prefer

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