| 主权项 |
1. An impact resistant polycarbonate polymer composition having improved resistance to polymer degradation comprising about 48 to about 75 weight percent of an aromatic polycarbonate in admixture with about 52 to about 25 weight percent of an elastomer-modified graft copolymer and optional polymeric flow promoter, based on the total weight of aromatic polycarbonate, elastomer-modified graft copolymer, and polymeric flow promoter, wherein the elastomer-modified graft copolymer is prepared by a process comprising:
emulsion polymerizing a monomer mixture comprising at least butadiene monomer in the presence of tetrasodium pyrophosphate and a surfactant selected from the group consisting of substituted or unsubstituted alkyl sulfonates, alkylaryl sulfonate, alkyl sulfates, alkylaryl sulfates, alkyl phosphate, alkylaryl phosphates, and mixtures thereof, thereby forming a diene polymer; and grafting one or more monomers onto the diene polymer, thereby forming a latex composition comprising an elastomer-modified graft copolymer, which latex composition has an alkaline pH, and coagulating the latex composition preliminary to admixture with the aromatic polycarbonate; wherein, after emulsion polymerization and prior to coagulating the latex composition with a salt coagulant, adjusting the pH of the latex composition comprising the elastomer-modified graft copolymer by introducing an acid, not a buffer, to obtain a pH of about 3.0 to about 6.8, wherein the acid has a pKa of less than 3.0; wherein after aging molded ISO tensile bars of the polycarbonate composition in an oven for 1000 hours at 90±2° C. and 95±3% RH, the melt flow rate (MFR) does not change by more than 5.0 g/10 min units measured in accordance with ISO 1133 standard at 230° C. using a 3.8 kg load and 300 sec dwell time. |
