Synthesis Of PTA-Polyester Diol And Its Application In Polyurethane Elastomer

Polyurethanes(PU), whose molecular chain containes urethane groups, are formed by the step-growth polymerization. PU materials include elastomers, foams, coatings, adhesives, fibers and so on, which have been widely applied in various fields. The performance of polyurethane elastomers(PUE) are between plastic and rubber. The hardness, tensile strength, elongation at break of PUE are adjusted, and the abrasion resistance of PUE is well. Poly(ε-caprolactone) and polyethylene adipate diol as two commercial polyester diol are widely used in the preparation of PUE. But the polyester diol synthesized with terephthalic acid(PTA) has been seldom reported in the preparation of PUE. So the synthesis and application of the polyester diol was carefully researched in the paper.Firstly, according to the carrier-gas melting esterification, by changing the molar ratio of diol to diacid. a series of PTA-polyester diols were synthesized from PTA with ethylene glycol(EG) or 1,4-butanediol(BDO) or diethylene glycol(DEG) or EG/BDO mixed diol or EG/DEG mixed diol or BDO/DEG mixed diol. The suitable kinds polyester diols, which could be used in PUE, were chosen by studying the synthesis technology and product characteristic of the above-systhesized polyester diols and taking into consideration the prepolymerization temperature in the preparation of PUE. The results showed:(1) the melting point of the polyester diols, which were synthesized by PTA with EG or BDO or EG/BDO, was above 120℃,so the polyester diols were not suitable for the preparation of PUE. Though the melting point of polyester diols synthesized by PTA and BDO/DEG was relatively lower, BDO was easily lost in the synthesis process of the polyester diol. The molting point of polyester diols, which were synthesized by PTA with DEG or EG/DEG mixed diol, was lower than 90 ℃, and the polyester diols were liquid at room temperature and suitable for the preparation of PUE.(2) The mixture of PTA and DEG(EG/DEG) as raw materials was first heated at 220?5℃ for some time in N2 before the clear pont of the synthesis system was obversed. Then the reaction temperature was increased up to 230?5℃. Finally the synthesis reaction carried on at 230?5℃ for some time in N2, and the synthesis reaction was stoped when the acid value of the synthesis system was below 2mg KOH/g. The hydroxyl value of polyester diols prepared with PTA and DEG was in the range of 70~190mgKOH/g, and that of polyester diols prepared with PTA and DEG/EG was among 120?20mgKOH/g.(3)When PUE was systhesized with the above-mentioned polyester diols and toluene diisocyanate(TDI) and 4,4’- methylenebis(ortho-chloroaniline)(MOCA), the results were as follows: the tensile strength of PUE prepared with higer hydroxyl-value polyester diol systhesized of PTA and DEG was superior to that of PUE prepared with higer hydroxyl-value polyester diol syntesed of PTA and DEG, and the elongations at break of PUE was just opposite, but the comprehensive performances of PUE prepared by using polyester diol systhesized of PTA and DEG were superior to that of PUE prepared by using polyester diol systhesized of PTA and EG/DEG. XRD showed that the intensity of diffraction peak at 43° for PUE prepared by using polyester diol systhesized of PTA and DEG was higher that PUE prepared by using polyester diol systhesized of PTA and EG/DEG. DSC showed that Tg of all systhesized PUE samples was above 0℃. Simultaneous thermal analysis showed that thermal decomposition temperature of all systhesized PUE samples was above 260℃ at 5% of weight loss.On the basis of the above experiment, when PTA/adipic acid(AA) molar ratio and EG/DEG molar ratio were both fixed at 1:1, by controlling the proportion between dicarboxyl acid mixture and glycol mixture, a series of copolyester diols were systhesized and the performance at room temperature was studied. The copolyester diol of hydroxyl-value 102.96 mg KOH/g was chosed to prepare PUE with TDI and MOCA. The results were as follows:(1) all systhesized samples of copolyester diols were liquid at room temperature.(2) The tensile strength of PUE prepared by using copolyester diol was up to 22.74 MPa and its elongation at break was up to 558%, But its comprehensive performance was slightly lower than that of PUE prepared by using polyester diol systhesized of PTA and DEG.(3) XRD showed that diffraction peak at 43° was not observed. DSC showed that Tg of all systhesized PUE samples was below 0℃. Simultaneous thermal analysis showed that thermal decomposition temperature of all systhesized PUE samples was above 260℃ at 5% of weight loss.