Hydrostability of polycarbonate polyester composition

A thermoplastic composition with improved hydrostability, comprising:

• about 31.3 percent by weight of polybutylene terephthalate prepared from dimethyl terephthalate and 1,4-butane diol in the presence of phosphoric acid (PA) and 50 to 300 ppm of tetraisopropyl titanate (TPT), wherein the polybutylene terephthalate has an intrinsic viscosity of 1.25 dL/min and a melting temperature of 225° C. and wherein the molar ratio between PA and TPT in the polybutylene terephthalate is 0.65:1;
• about 37.41 percent by weight of bisphenol A polycarbonate having a molecular weight of about 30,000 g/mol;
• about 19.16 percent by weight of bisphenol A polycarbonate having a molecular weight of about 22,000 g/mol;
• about 0.05 percent by weight of pentaerythritol betalaurylthiopropionate;
• about 0.08 percent by weight of pentaerythritol-tetrakis(3-(3,5-di-tert-butyl-4-hydroxy-phenyl-)propionate);
• about 2 percent by weight of linear low density polyethylene;
• and
• about 10 percent by weight of methylmethacrylate-butadiene styrene impact modifier;
• wherein:
• the polybutylene terephthalate is not produced from recycled polyethylene terephthalate;
• all weight percents are based on the total weight of the composition;
• no quencher for the catalyst complex is added to the thermoplastic composition;
• and
• the thermoplastic composition gives a Delta Vicat Softening temperature according to ASTM D1525 of less than 10° C. and retains 33 percent of its impact strength according to ASTM D256 after 1000 hours of hydroaging at 80° C. and 80 percent relative humidity as compared to a thermoplastic composition that is identical in all respects except that the catalyst used to prepare the polybutylene terephthalate is tetraisopropyl titanate.