Crystalline polyester resins and processes for their preparation

A process for the preparation of a linear poly(1,4-butylene terephthalate) resin, the process comprising:

• heating at a temperature of about 195° C. to about 230° C. a mixture of terephthalic acid and 1,4-butanediol in the presence of a polyesterification catalyst composition until water substantially ceases to be evolved, said mixture comprising from about 350 to about 120 mole percent butanediol to terephthalic acid;
• applying a vacuum and continuing heating until an oligomeric mixture having a first selected viscosity and a first selected level of acid end groups is formed;
• and
• continuing the heating under vacuum and removing byproduct 1,4-butanediol until a poly(1,4-butylene terephthalate) resin having a second viscosity and a second selected level of acid end groups is formed.

A process for the preparation of a linear poly(1,4-butylene terephthalate) resin, the process comprising the steps of:

• directly esterifying a reaction mixture consisting essentially of terephthalic acid, 1,4-butanediol, and an optional catalyst until the clearing point;
• pre-polymerizing the cleared reaction to produce an oligomeric mixture having an acid end group level of about 0.5 to about 100 meq/kg, and an intrinsic viscosity of about 0.05 to about 0.70 dl/g as measured in 60/40 phenol/1,1,2,2-tetrachloroethane by weight at 25° C.;
• and
• polycondensing the oligomeric mixture to produce a poly(1,4-butylene terephthalate) having an acid end group level of about 10 to about 40 meq/kg and an intrinsic viscosity of greater than or equal to about 0.80 dl/g as measured in 60/40 phenol/1,1,2,2-tetrachloroethane by weight at 25° C.