Polycarbonate compositions comprising elastomer-modified graft copolymer prepared by emulsion polymerization

1. An impact resistant polycarbonate composition having improved resistance to polymer degradation comprising an aromatic polycarbonate in admixture with an elastomer-modified graft copolymer that is a product of a process comprising emulsion polymerization in the presence of an electrolyte that is a potassium or sodium salt of an anion selected from the group consisting of phosphate or bicarbonate, and combinations thereof, wherein the elastomer-modified graft copolymer in the impact resistant polycarbonate composition contains residual amounts of the electrolyte;

wherein after aging in an oven for 1000 hours at 90±2° C. and 95±3% RH, the melt flow rate (MFR) of the polycarbonate composition does not change by more than 5.0 g/10 minutes units measured in accordance with ISO 1133 standard at 230° C. using a 3.8 kg load and 300 sec dwell time.

2. The composition of claim 1 wherein the electrolyte is selected from the group consisting of disodium phosphate, dipotassium phosphate, monosodium phosphate, monopotassium phosphate, trisodium phosphate, tripotassium phosphate, sodium bicarbonate, potassium bicarbonate, and combinations thereof.

3. The composition of claim 1 , wherein the electrolyte is a potassium or sodium salt of phosphoric acid.

4. The composition of claim 1 wherein after aging in an oven for 1000 hours at 90±2° C. and 95±3% RH, the polycarbonate composition exhibits a change in the melt flow rate (MFR) that is at least 3 g/10 minutes less than the change in the same composition in which said electrolyte is replaced by an equal amount by weight of tetrasodium pyrophosphate, wherein melt flow rate is measured in accordance with ISO 1133 standard at 230° C. using a 3.8 kg load and 300 sec dwell time.

5. The composition of claim 1 wherein the elastomer-modified graft copolymer is a product of a process comprising emulsion polymerization in the absence of tetrasodium pyrophosphate.

6. The composition of claim 1 wherein the elastomer-modified graft copolymer comprises an elastomeric substrate and a non-elastomeric superstrate grafted to the elastomeric substrate.

7. The composition of claim 1 wherein the elastomer-modified graft copolymer comprises, prior to grafting, a diene polymer having a glass transition temperature of 0° C. or less.

8. The composition of claim 6 wherein the elastomeric substrate comprises a diene polymer selected from the group consisting of a polymer that is the reaction product of conjugated dienes, copolymers containing at least about 50 weight % of a conjugated diene, copolymers of alkyl acrylates with styrene, acrylonitrile and/or butadiene, and mixtures thereof.

9. The composition of claim 6 , wherein the non-elastomeric superstrate comprises a thermoplastic polymer that is capable of readily wetting the polycarbonate in the composition.

10. The composition of claim 6 wherein the elastomeric substrate comprises repeat units derived from butadiene and the non-elastomeric superstrate is a copolymer comprising repeat units derived from a monovinylaromatic monomer.

11. The composition of claim 6 wherein the elastomer-modified graft copolymer is made by a process in which agglomerated polybutadiene latex is grafted with a monomer mixture comprising styrene and optional monomer selected from the group consisting of methyl acrylate, methyl methacrylate, acrylonitrile, alpha-methyl styrene and combinations thereof.

12. The composition of claim 11 wherein the monomer mixture comprises styrene and acrylonitrile in a ratio of 5:1 to 1:1 by weight.

13. The composition of claim 11 wherein the weight ratio of the polymer to the thermoplastic polymer of the superstrate is about 4:1 to 1:4.

14. The composition of claim 1 comprising, in admixture, about 20 to about 90 weight percent of the aromatic polycarbonate and about 80 to about 10 weight percent of elastomer-modified graft copolymer and optional polymeric flow promoter, based on the total weight of polycarbonate, elastomer-modified graft copolymer, and optional polymeric flow promoter.

15. The composition of claim 1 comprising, in admixture, about 48 to about 75 weight percent of the aromatic polycarbonate and about 52 to about 25 weight percent of elastomer-modified graft copolymer and optional polymeric flow promoter, based on the total weight of polycarbonate, elastomer-modified graft copolymer, and optional polymeric flow promoter.

16. The composition of claim 14 wherein the polymeric flow promoter is a styrene-acrylonitrile copolymer, poly(alkyl (meth)acrylate), polystyrene, alkyl (meth)acrylate-styrene-acrylonitrile copolymer, alpha-methyl styrene-acrylonitrile copolymer or a combination thereof.

17. The composition of claim 16 wherein the polymeric flow promoter is a styrene-acrylonitrile copolymer.

18. The composition of claim 1 wherein the elastomer-modified graft copolymer is a product of a process comprising emulsion polymerization employing a surfactant selected from the group consisting of substituted or unsubstituted alkyl sulfonates, alkylaryl sulfonates, alkyl sulfates, alkylaryl sulfates, alkyl phosphate, alkylaryl phosphates, and mixtures thereof.

19. The composition of claim 18 wherein the surfactant is an alkyl diphenyl oxide disulphonate.

20. The composition of claim 18 wherein the elastomer-modified graft copolymer is a product of a process comprising polymerization in the absence of any emulsifiers that are alkali metal salts of fatty acids, alkali metal carbonates, amines, or ammonium salts.

21. An impact resistant polycarbonate composition having improved resistance to polymer degradation comprising, in admixture, about 48 to about 75 weight percent of an aromatic polycarbonate and about 52 to about 25 weight percent of an elastomer-modified graft copolymer and optional polymeric flow promoter, based on the total weight of polycarbonate, elastomer-modified graft copolymer, and polymeric flow promoter, wherein the elastomer-modified graft copolymer is a product of a process comprising:

Emulsion polymerization in which, before grafting, a reaction mixture comprising butadiene is polymerized in the presence of an electrolyte that is a potassium or sodium salt of an anion selected from the group consisting of phosphate or bicarbonate, and combinations thereof, further in the presence of a surfactant selected from the group consisting of substituted or unsubstituted alkyl sulfonates, alkylaryl sulfonates, alkyl sulfates, alkylaryl sulfates, alkyl phosphate, alkylaryl phosphates, and mixtures thereof, wherein each alkyl group has 1-20 carbon atoms and each aryl group has 6-12 carbon atoms; and

agglomeration of the resultant polybutadiene to a polybutadiene latex having a larger particle size;

wherein the elastomer-modified graft copolymer is made by a process in which the agglomerated polybutadiene latex is grafted with a comonomer mixture comprising styrene and acrylonitrile; and

wherein the elastomer-modified graft copolymer in the impact resistant polycarbonate composition contains residual amounts of the electrolyte and wherein after aging in an oven for 1000 hours at 90±2° C. and 95±3% RH, the melt flow rate (MFR) of the polycarbonate composition does not change by more than 5.0 g/10 minutes units measured in accordance with ISO 1133 standard at 230° C. using a 3.8 kg load and 300 sec dwell time.

22. A method of preparing a polycarbonate composition having improved resistance to polymer degradation comprising:

emulsion polymerization of a monomer mixture comprising a diene monomer in the presence of an electrolyte that is a potassium or sodium salt of an anion selected from the group consisting of phosphate or bicarbonate, and combinations thereof, thereby producing a latex of a diene polymer;

agglomeration of the latex of the diene polymer to a larger particle size;

grafting monomers onto the agglomerated diene polymer of the latex to obtain an elastomer-modified graft copolymer; and

admixing an aromatic polycarbonate with the elastomer-modified graft copolymer and an optional polymer flow promoter; wherein the elastomer-modified graft copolymer in the impact resistant polycarbonate composition contains residual amounts of the electrolyte and wherein after aging in an oven for 1000 hours at 90±2° C. and 95±3% RH, the melt flow rate (MFR) of the polycarbonate composition does not change by more than 5.0 g/10 minutes units measured in accordance with ISO 1133 standard at 230° C. using a 3.8 kg load and 300 sec dwell time.

23. The method of claim 22 , wherein emulsion polymerization is carried out in the presence of an electrolyte that is selected from the group consisting of disodium phosphate, dipotassium phosphate, monosodium phosphate, monopotassium phosphate, trisodium phosphate, tripotassium phosphate, sodium bicarbonate, potassium bicarbonate, and combinations thereof, further in the presence of a surfactant selected from the group consisting of substituted or unsubstituted alkyl sulfonates, alkylaryl sulfonates, alkyl sulfates, alkylaryl sulfates, alkyl phosphate, alkylaryl phosphates, and mixtures thereof, wherein each alkyl group has 1-20 carbon atoms and each aryl group has 6-12 carbon atoms.

24. The method of claim 23 , further comprising, before grafting, agglomerating the diene polymer to a larger average particle size, coagulating the elastomer-modified graft copolymer, and then concentrating and drying the coagulated elastomer-modified graft copolymer.

25. The method of claim 23 wherein the aromatic polycarbonate is admixed with the elastomer-modified graft copolymer by compounding optionally further with a polymeric flow promoter, wherein the polymeric flow promoter comprises repeat units derived from monomers selected from the group consisting of alkyl (meth)acrylate, styrene, acrylonitrile, alpha-methylstyrene and combinations thereof.

26. An article made from the composition of claim 1 .

27. The article of claim 26 wherein the article is a molded automotive part selected from the group consisting of spoilers, instrument panels, instrument panel retainers, interior trim, truck roof fairings, truck hoods, car hoods, bumpers, minor housings, and electroplated wheel covers, hub caps, emblem logos, exterior trim, and door handles.

28. The composition of claim 21 , wherein the electrolyte is a potassium or sodium salt of phosphoric acid.