Process for preparation of polyester-based polymers

A process for preparing polyester polymers comprising the steps of:

• (a) esterifying either a naphthalene dicarboxylic acid, a dicarboxylic acid containing naphthalene dicarboxylic acid, a terephthalic acid or ester derivatives thereof, with at least one glycol selected from the group consisting of ethylene glycol, propanediol, butanediol, pentanediol, hexandiol and derivatives thereof to produce esterified compounds or its low molecular weight polymers;
• and
• (b) polycondensing continuously the resultant esterified product of step (a) to produce polyester polymers;
• wherein in the above preparing process a composite polymerization catalyst is used which is prepared by reacting at least one compound of cobalt and at least one compound of titanium selected from the group consisting of a titanate compound, a phosphite complex compound thereof and mixtures thereof, in the presence of a solution comprising at least one alcohol compound selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol, and mixtures thereof, the titanate compound being represented by the following general formula I:
• (RO)4Ti Formula I
• wherein each R is independently the same or different and is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, acetylisopropyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, decyl, dodecyl, tridecyl, octadecyl, stearyl, allyl, 2,2-diallyloxymethylbutyl, cyclopentyl, cyclohexyl, naphthyl, phenyl, benzyl, and dodecylbenzyl.