COPOLYESTERS .7. THERMAL TRANSITIONS OF POLY(BUTYLENE TEREPHTHALATE-CO-ISOPHTHALATE-CO-ADIPATE)S

The copolyesters of 1,4-butanediol, terephthalic acid, isophthalic aci d, and adipic acid with different compositions were prepared by melt p olycondensation. The intrinsic viscosity of the copolyesters was contr olled to be about 0.7-1.0 dL/g. Their second-run thermal properties we re determined by DSC. The composition was found to be a major factor i n the determination of the thermal transitions. The effect of the comp osition on the glass transition temperature and melt transition temper ature was interesting. The glass transition temperature was found to b e dependent mainly on the content of adipic acid. As the content of ad ipic acid increased, the glass transition decreased. When the content of terephthalic acid was not less than 35 mol % based on the total dia cid monomers, the melting temperature was dependent mainly on the cont ent of terephthalic acid and increased with increase of the content of terephthalic acid. When the content of terephthalic acid was less tha n 35 mol %, the melt temperature of the copolyesters did not follow a simple rule. However, the effect of the composition on their melting e nthalpy showed no simple trend. (C) 1994 John Wiley & Sons, Inc.