Transparent graft copolymers based on acrylate soft phases

1. A graft copolymer B, built up from:

(B1) 15 to 45 wt.-%, based on graft copolymer B, of a non-cross-linked graft substrate polymer B1 having a glass transition temperature T G below 25° C. (DSC, heating rate: 5K/min), consisting of polymerized units derived from monomers B11, B12, and optionally B13:

(B11) from 95 to 99.5 wt.-%, based on the total weight of B11, B12, and B13, of at least one C 1 -Ci 8 -alkyl acrylate;

(B12) from 0.5 to 5 wt.-%, based on the total weight of B11, B12, and B13, of at least one bifunctional, crosslinking monomer which contains two copolymerizable double bonds which are not conjugated in 1,3 positions; and

(B13) from 0 to 4.5 wt.-%, based on the total weight of B11, B12, and B13, of at least one other copolymerizable, monoethylenically unsaturated monomer; and

(B2) 55 to 85 wt.-%, based on graft copolymer B, of at least one polymer B2 having a glass transition temperature T G above 25° C., grafted from the graft substrate polymer (B1), consisting of polymerized units derived from monomers B21 and optional comonomers B22:

(B21) from 65 to 100 wt.-% of at least one vinylaromatic monomer or its mixture with at least one C 1 -C 8 -alkyl-(meth)acrylate; and

(B22) from 0 to 35 wt.-% of at least one other monofunctional comonomer;

where components B1 and B2 give 100 wt.-% in total, and

wherein

the graft substrate polymer B1 has a gel content (non-soluble fraction in toluene) below 5 wt.-%, based on the total amount of B1; and

the second double bond of the bifunctional, crosslinking monomer B12 is the active site from which polymerized units derived from monomer B21 and optionally comonomer B22 are grafted.

2. The graft copolymer B according to claim 1 having a transmittance T of at least 75% (determined according to ASTM D1003) and a haze coefficient below 10% (determined according to ASTM D1003-95).

3. The graft copolymer B according to claim 1 , wherein monomer B11 is ethyl acrylate, 2-ethylhexyl acrylate, n-butyl acrylate, or mixtures thereof.

4. The graft copolymer B according to claim 1 , wherein the bifunctional, crosslinking monomer B12 is allyl methacrylate (AMA) or dicyclo-pentadienyl acrylate (DCPA).

5. The graft copolymer B to claim 1 , wherein monomer B21 is styrene, α-methylstyrene, or a mixture of styrene or a-methylstyrene with methyl methacrylate.

6. The graft copolymer B according to claim 1 , wherein comonomer B22 is maleic anhydride or acrylonitrile.

7. The graft copolymer B according to claim 1 , wherein polymer B2 has been built up from styrene, or from a mixture consisting of 65 to 85 wt.-% styrene and 15 to 35 wt.-% acrylonitrile, maleic anhydride, or methyl methacrylate.

8. The graft copolymer B according to claim 1 , wherein monomer B13 is not present.

9. The graft copolymer B according to claim 1 , built up from:

(B1) 20 to 40 wt.-% of graft substrate polymer B1 and

(B2) 60 to 80 wt.-% of polymer B2.

10. A process for the preparation of the graft copolymer B according to claim 1 , which comprises the following steps:

(i) free radical aqueous emulsion polymerization of monomers B11, B12, and optionally B13 in presence of an initiator PI-1; and

(ii) grafting monomer B21 and optional comonomer B22 from graft substrate polymer B1 obtained in step (i) by free radical emulsion or solution polymerization in presence of an initiator PI-2;

where the initiators PI-1 and PI-2 can be the same or different compounds, and

wherein

step i) is performed in presence of 0.85 to 2 wt.-% of at least one chain transfer agent, based on the total amount of monomers B11, B12, and B13; and

in step ii):

the amount of the initiator PI-2 is 0.1 to 3 wt.-%, preferably 0.5 to 2 wt. %, relative to the total content of monomers B21 and B22; and

monomer B21 and, if present, comonomer B22 are fed continuously to the reaction mixture over 7 to 20 hours at a temperature of from 50 to 100° C.

11. The process according to claim 10 , wherein in step i) the chain transfer agent is added stepwise in two or more portions.

12. The process according to claim 10 , wherein in step ii) the monomer, and optional initiator, feed is within 9 to 15 hours.

13. A graft copolymer B obtained by the process according to claim 10 .

14. A molding composition comprising at least one graft copolymer B according to claim 1 , and optionally additives and/or auxiliaries C.

15. The molding composition according to claim 14 , further comprising at least one thermoplastic polymer A having a glass transition temperature above 25° C.

16. The molding composition according to claim 15 , wherein the thermoplastic polymer A is selected from standard polystyrene (GPPS, homopolystyrene), styrene-acrylonitrile copolymers (SAN), a-methylstyrene-acrylonitrile copolymers (AMSAN), styrene-maleic anhydride copolymers (SMSA), and styrene-methyl methacrylate copolymers (SMMA).

17. The molding composition according to claim 15 , comprising:

5 to 60 wt.-% of at least one graft copolymer B,

30 to 95 wt.-% of at least one thermoplastic polymer A, and

0 to 10 wt.-% of additives and/or auxiliaries C,

wherein the sum of the amounts of components A, B, and, if present, C, makes 100 wt.-%.

18. A shaped article comprising the molding composition according to claim 14 .

19. The molding composition according to claim 14 for the production of a household item, an electronic component, household equipment, garden equipment, medical-technology equipment, a motor-vehicle component, and a bodywork part.