Polyester compositions which crystallize rapidly

摘要

Polyalkylene terephthalates containing 0.5-30% by weight of oligomeric carboxylic acid polyesters have a higher crystallization speed and thus allow lower mold temperatures and shorter injection cycles. The polyalkylene terephthalates generally have intrinsic viscosities in excess of about 0.4 dl/g in 1:1 phenol tetrachloroethane at 25 DEG C. and are at least about 90 mol % terephthalic acid based. The oligomer additive is based on carboxylic acids, with sebacic and adipic being preferred, and aliphatic, cycloaliphatic or araliphatic dihydric alcohols. This additive has a minimum polymerization degree of 2 and a maximum number-average molecular weight of about 6000. Faster crystallization rates can be imparted to polyalkylene terephthalates by mixing them with the ester additive and melt homogenizing the mixture.