SYNOPSISThe copolyesters of 1,4-butanediol, terephthalic acid, isophthalic acid, and adipic acid with different compositions were prepared by melt polycondensation. The intrinsic viscosity of the copolyesters was controlled to be about 0.7-1.0 dL/g. Their second-run thermal properties were determined by DSC. The composition was found to be a major factor in the determination of the thermal transitions. The effect of the composition on the glass transition temperature and melt transition temperature was interesting. The glass transition temperature was found to be dependent mainly on the content of adipic acid. As the content of adipic acid increased, the glass transition decreased. When the content of terephthalic acid was not less than 35 mol % based on the total diacid monomers, the melting temperature was dependent mainly on the content of terephthalic acid and increased with increase of the content of terephthalic acid. When the content of terephthalic acid was less than 35 mol %, the melt temperature of the copolyesters did not follow a simple rule. However, the effect of the composition on their melting enthalpy showed no simple trend.
I NTRO DUCT10 NThe performance of a hot melt adhesive can be controlled by its thermal transitions including glass transition temperature ( T,) , melting temperature ( T,) , and melting enthalpy.'.' A lower Tg ameliorates flexibility and thus gives better low-temperature performance. A higher T, increases the heat resistance, but always gives a higher melt viscosity, which will influence the processability. A higher melting enthalpy improves the heat resistance and the lap shear strength, but may give poorer adhesion.The copolyesters of 1,4-butanediol and two different diacids have been considered to be used as hot melt adhesives.'-' The thermal transitions can be controlled by the chemical composition to some extent. However, it will be more flexible to incor- CCC 0021-8995/94/060999-06 porate a third diacid component to regulate the properties. Based on this observation, the copolyesters of 1,4-butanediol, terephthalic acid, isophthalic acid, and adipic acid have been used as hot melt adhesives.'-13 In our laboratory, some poly (butylene terephthalate-co-isophthalate-co-adipate ) s with a molar composition of 1,4-butanediol : terephthalic acid : isophthalic acid : adipic acid = 1 : 0.45 : 0.30 : 0.25 were prepared as hot melt adhesives.14 These copolyesters were designed to have a T, of about 110°C to fit a typical hot melt gun for the shoe sole application. In the screening of the suitable copolyesters, we also found that the Tg and the melting enthalpy were also important in determining their performance in addition to the T,.There are many' different applications for copolyester-type hot melt adhesives. To optimize the performance for different applications, it is important to understand the factors influencing the thermal transitions of the copolyesters. In this article, various poly (butylene terephthalate-co-isophthalate-co-adipate) s with a wide composition range...
