Production of tetramethylene terephthalate polymers using 225° to 248° C. polycondensation temperature

Claim 1

A process for preparing a polyester comprising; transesterifying 1,4-butanediol and at least one dialkyl benzenedicarboxylate consisting of 80 to 100 mole percent of at least one dialkyl terephthalate and 0- 20 mole percent of at least one ester selected from dialkyl phthalates and dialkyl isophthalates, each of said alkyls of said dialkyl benzenedicarboxylate being selected from alkyl groups having 1 to 4 carbon atoms, by contacting said 1,4-butanediol and said at least one dialkyl benzenedicarboxylate with a transesterification and polycondensation catalyst consisting essentially of a tetraalkyl titanate of the formula Ti(OR) 4 wherein R is an alkyl group having 1 to 6 carbon atoms, said contacting being carried out at a temperature within a range of 130° C. to 248° C. at substantially atmospheric pressure; and thereafter subjecting the resulting mixture in a melt state to a temperature within the range of 225° to 248° C. and reduced pressure for a time within the range of 2 to 8 hours to effect polycondensation, said temperature during said polycondensation at no time exceeding 248° C.