Synthesis And Crystallization Behaviors Of Biodegradable Poly(Butylene Succinate-Co-Butylene Suberate) Copolymers

In this work, biodegradable homopolymer poly(butylene succinate)(PBS), poly(butylene suberate) (PBSub) and their random copolymers poly(butylene succinate-co-butylene suberate) (P(BS-co-BSub)) were synthesized from the monomers of butanediol, succinic acid and suberic acid via a two-step melt polycondensation method. The basic thermal behaviors, isothermal melt crystallization kinetics, crystal structure, spherulitic morphology and growth of PBS, PBSub and P(BS-co-BSub) were systematically investigated with Differential Scanning Calorimetry(DSC), Wide-angle X-Ray Diffraction (WAXD), and Polarizing Optical Microscope(POM).PBSub is a relatively novel biodegradable polyester which hasn’t been intensively reported. PBSub has a low glass transition temperature of about-61℃, a melting point of 55.2℃, and an equilibrium melting point of 61.4℃. The overall isothermal melt crystallization kinetics of PBSub may correspond to three-dimensional truncated sphere growth with athermal nucleation and an obvious spherulitic morphology is observed for PBSub.The crystal structure study with WAXD reveals that PBSub is highly crystalline, presenting a great crystallinity of about 55%. The thermogravimetric analysis study demonstrates that PBSub has both a high decomposition temperature of about 377℃at 5 wt% weight loss, suggesting its good thermal stability. It takes only six days for PBSub fully degraded in hydrolytic experiments, which demonstrates the biodegradablility of PBSub.Eleven samples with close molecular weight were synthesized and the influence of comonomer on the properties of homopolymer were studied in detail. It is found that the melting temperature and crystallization temperature of homopolymer move toward low temperature by the presence of comonomer. The presence of comonomer doesn’t change the overall isothermal melt crystallization kinetics of homopolymer and all the samples correspond to three-dimensional truncated sphere growth with athermal nucleation.The crystal structure of homopolymer remains unchanged despite the presence of comonomer, but the crystallinity becomes lower. Hoffman-Weeks plots suggest that comonomer may suppress the equilibrium melting point of homopolymer, which resuled in the decrease of spherulitic growth rates. All the samples show a good thermal stability.