Preparation And Properties Of Copolyesters Modified By 2-Methy-1,3-Propanediol

Low-melting point copolyester is a kind of new modified copolyester that has been researched and developed in recent years. Because its structure is similar to the ordinary polyester, it has good compatibility with ordinary polyester. At the same time, it has advantages of low melting point, good fluidity and affordable, and during the production of low-melting point copolyester products, the cost can be saved. Thus, the demand of low-melting point copolyester is increasing and it has a broad application prospect.In this paper, 2-methyl-1, 3-propanediol(MPO) as the third monomer or MPO and isophthalic acid(IPA) as the third monomer and fourth monomer respectively were added during the normal synthesis of poly(ethylene terephthalate)(PET) and poly(trimethylene terephthalate)(PTT). Then, a series of modified PET copolyesters and modified PTT copolyesters were prepared through the direct esterification melt polycondensation method. The viscosity average molecular weights of modified copolyesters were determined through viscosity method. The melt crystallization and rheological properties of modified copolyester were characterized by differential scanning calorimetry(DSC), orthogonal polarizing microscope(POM) and capillary rheometer.The test results of viscosity method showed that viscosity average molecular weights of modified PET and PTT copolyesters are in the range of 18000-23000g·mol-1 and 14000-29000g·mol-1, respectively. They all have reached polymer level.The test results of DSC indicated that melting temperature of modified PET and PTT copolyesters decrease. The melting temperature of modified PET copolyester with 15mol% MPO is 199.64℃, and decreases by 44.04℃ compared with the melting point of 243.68℃ of PET. The melting temperature of modified PTT copolyester is 201.78℃ containing 20mol% MPO, and decreases by 24.86℃ compared with the melting point of 226.64℃ of PTT. The melting point of modified copolyester with 20mol% MPO and 20mol% IPA decreases more obviously compared with that of homopolyester. The research results of non-isothermal crystallization showed that the crystallization temperature of modified copolyesters decreases and half crystallization time(21t) increases because of the addition of MPO. Additionally, Jeniorny method is mainly used to study the non-isothermal crystallization kinetics of modified copolyesters, and the results proved that crystallization rate constant(cZ) of modified copolyesters decreases compared with that of the homopolyester, and revealed the addation of MPO makes the crystallization rate of polyester become slower and the crystallization ability become worse.The observation results of POM showed that the modified copolyesters with MPO appear spherulite morphology and the spherulite size reduces with the MPO content increasing. While the modified PET copolyesters with MPO and IPA doesn’t appear spherulite structure, and the spherulite size of modified PTT copolyesters with MPO and IPA reduces, which furtherly showed that the crystallization abilities of modified copolyesters with MPO or MPO and IPA decline.The test results of capillary rheometer showed that the prepared modified copolyesters are pseudoplastic fluids. At the same shear rate, viscous flow activation energy of the modified copolyester melts is less than that of homopolyester, and this indicated that the viscosity-temperature dependence of modified copolyesters is lower than that of homopolyester.