The invention is directed to a thermoplastic condensation polymer chain extender additive package for reducing the molecular weight loss of a thermoplastic condensation polymer during a heated process comprising a chain extender composition selected from the group consisting of (a) a mixture of a chain extending agent and a water-bearing particulate material (b) a water-bearing particulate material surface treated with a chain extending agent or (c) a combination of (a) and (b). The water-bearing particulate material can be titanium dioxide pigment, the chain extending agent can be a multifunctional epoxy compound and the condensation polymer can be polyethylene terephthalate, polybutylene terephthalate or polycarbonate.