Modification Of Poly(Ethylene Succinate) And Poly(Ethylene Adipate) Through Copolymerization With Diethylene Glycol

Along with the rapid development of modern technology, the problems of environment pollution and resource shortage are becoming more conspicuous, and more and more attention has been paid to the field of biodegradable polymer materials. In this paper, biodegradable poly(ethylene succinate) (PES) and poly(ethylene adipate) (PEA) were synthesized by a two-step melt polycondensation method, and they were modified through the copolymerization with diethylene glycol (DEG) to prepare two kinds of copolyesters, i.e. poly(ethylene succinate-co-diethylene glycol succinate) (P(ES-co-DEGS)) and poly(ethylene adipate -co-diethylene glycol adipate) (P(EA-co-DEGA)). Meanwhile, kinds of techniques were used to investigate the effects of the introduction of DEG on chemical structure, crystal structure, thermal behaviors, crystallization morphology, thermal stability, and mechanical properties of polyesters. It is found that:1.In the series of P(ES-co-DEGS), the introduction of DEGS unit enables PES have a better chain flexibility and a lower glass transition temperature (Tg), and depress the values of melting point (Tm), equilibrium melting point (Tm0), and crystallinity (Xc), while the crystal structure is unchanged; the isothermal crystallization results were analyzed by the Avrami equation, and it is suggested that either the increment of the crystallization temperature (Tc) or DEGA content will not affected the crystallization mechanism, but it will prolong the crystallization half-time (t0.5) values of the samples and depress the isothermal crystallization rate compared to PES homopolymer. The spherulitic morphologies of PES and P(ES-co-DEGS) were studied through polarizing microscope (POM) measurement, it is found that all the samples show an obvious Maltase cross phenomenon obvious, and the variations of spherulitic growth rates (G) and Tc are typical inverted bell shapes. And the crystallization morphology reveals that the depressed nucleation density and the larger size of the spherulites were found with the increasing of Tc.2. Adipate, ethylene glycol, and DEG were used to prepared a series of PEA and P(EA-co-DEGA) copolymers with high molecular weight through a melt polycondensation method. The wide-angle X-ray diffraction (WAXD) results suggest that the introduction of the uncrystallizable DEGA unit has not affected the crystal structure of all the samples, but it leads to a depressed Xc for the P(EA-co-DEGA) copolymers, compared to PEA homopolymer. It is found that the introduction of DEGA unit has no effect on the chain mobility for P(EA-co-DEGA) copolymers compared to PEA, leading to a unchanged Tg, but it depresses the cold crystallization, melt crystallization, and melt behaviors with the DEGA content. Similar to the series of P(ES-co-DEGS), the isothermal crystallization rate is depressed by the introduction of the uncrystallizable DEGA unit, while the crystallization mechanism is unchanged. For the results of the tensile testing, PEA and P(EA-co-DEGA) copolymers show a very good tensile properties, and the elongation at break are more than 1000%; meanwhile, the increment of DEGA content will keep on developing the tensile properties at some extent, and the outstanding mechanical properties can provide an important theoretical foundation for obtaining a high flexibility material.