Process for preparing polyethylene naphthalate

摘要

The present invention relates to a process for preparing a polyethylene naphthalate possessed with high viscosity, characterized by sloving of various problems of the prior art by controlling the rate of the polycondensation reaction. Particularly, the present invention provides a process for preparing polyethylene naphthalate from an esterification reaction product of naphtalene dicarboxylic acid or an alkyl ester thereof and a diol, which comprises polycondensing the esterification reaction product in the presence of a polycondensation catalyst in two steps wherein the first step is carried out at a pressure ranging from 500 to 30 torr and the second step is carried out at a pressure ranging from 10 to 0.1 torr with controlling the reaction rate such that the differential increase of the intrinsic viscosity of the resultant polymer can satisfy the following equations: IV(t1)-IV(t0)<0.4 dl/g(1) IV(t2)-IV(t0)>0.3 dl/g(2) wherein: IV(t0) represents the intrinsic viscosity at the beginning of the second step polycondensation, IV(t1) represents the intrinsic viscosity at 90 minutes after the beginning of the second step polycondensation, and IV(t2) represents the intrinsic viscosity at 180 minutes after the beginning of the second step polycondensation.