Synthesis, Crystallization Behaviors, And Properties Of Biodegradable Poly (Ethylene Succinate) Based Copolyesters

Poly(ethylene succinate) (PES), one of the most promising biodegradable polyesters, has attracted more and more attentions in recent years as it shows excellent properties; moreover, the monomers for the synthesis of PES can be prepared from renewable resources. In this dissertation, a series of PES-based copolyesters were obtained through copolymerization method to meet different demands. In addition, the crystallization behaviors and properties of PES-based copolyesters were investigated in detail.1. Poly(ethylene succinate-co-ethylene suberate) (PESSub) copolyestersA series of PESSub copolyesters with high molecular weights were successfully synthesized and the effects of ethylene suberate (ESub) units on the properties of PESSub and PES were studied with various techniques. The copolymers with higher ESub component showed greater elongation at break and lower Young's modulus. PESSub showed slower hydrolytic degradation rates compared with that of PES. The isothermal cold crystallization mechanism of PESSub remained with increasing the ESub composition while the isothermal cold crystallization rates decreased. In addition, the melt crystallization kinetics and morphology of poly(ethylene suberate) (PESub)were also studied, ring-banded spherulite and a crystallization regime III to II transition were found for PESub in the studied temperature ranges.2. Poly(ethylene succinate-co-ethylene sebacate) (PESSe) copolyestersThree novel bio-based poly(ethylene succinate-co-ethylene sebacate)(PESSe) copolyesters containing different ethylene sebacate (ESe) fractions were successfully synthesized. The tensile properties, hydrolytic degradation and the crystallization behaviors of the synthesized PESSe copolyesters were systematically studied. The thermal stability of PES and PESSe was high and slightly improved with the increasing content of ESe. PES and PESSe all displayed good mechanical properties, which varies with the ESe content.With the increase of ESe content, elongation at break increased while the yield strength and Young's modulus decreased for PESSe and PES. During the hydrolytic degradation process, the hydrolytic rates of PESSe became gradually slower with increasing the ESe content and were all slower than that of PES. The SEM images of the samples surfaces before and after the hydrolytic degradation confirmed again a decreased hydrolytic degradation rate with increasing the ESe content. With increasing the ESe content, the glass transition temperature, melting point, and heat of fusion for PESSe showed decreased tendency. With the increase of ESe content, the isothermal melt crystallization rate, spherulitic growth rate and the nucleation density decreased while the isothermal melt crystallization mechanism remained.PESSe displayed lower nonisothermal cold crystallization rate compared with that of PES. Like PES, the nonisothermal cold crystallization kinetics of PESSe copolymers can also be analyzed by the Ozawa equation. Effect of the comonomer structure on the crystallization behaviors and hydrolytic degradation of the PES-based copolymers was also studied. It was found that PESSub showed faster crystallization rate while the PESSe copolyesters had better chain mobility. More importantly, longer comonomer length led to slower degradation rate of PES-based copolyesters. Thus, the properties of PES-based copolyesters could be well adjusted by the structure and content of comonomers.3. Poly(ethylene succinate-co-isosorbide succinate) (PEIS) copolyestersA series of bio-based PEIS copolymers were synthesized, the influence of isosorbide succinate (IS) unit on the crystallization behavior and spherulitic growth of PEIS was studied. The incorporation of IS improved the glass transition temperature of PEIS while lowered the melting point and equilibrium melting point. Crystal structure of PES was hardly modified but the degree of crystallinity decreased with the increasing IS content. PEIS showed decreased isothermal melt crystallization rates compared with that of PES. The nucleation density and spherulitic growth rates of PEIS decreased with increasing IS content. The crystallization regime III to II transition was found for PES and PEIS, and the transition temperature decreased with the increasing IS content.4. Poly(ethylene succinate) copolyesters with n-octyl branchesBranched poly(ethylene succinate) copolymers with low contents of n-octyl pendant group being side chains were successfully synthesized. The melt isothermal crystallization behavior, basic thermal behavior, rheological behavior, and hydrolytic degradation of branched PES were systematically studied and compared with those of linear PES. Regardless of side chains content, branched PES displayed the same crystal structure as linear PES;moreover, the degree of crystallinity decreased slightly with increasing the content of side chains. The glass transition temperature, melting point, and heat of fusion of branched PES were smaller than those of linear PES and further decreased with the increase of side chain content. With the incorporation of branches, decreased isothermal melt crystallization rates and spherulitic growth rates were observed, but the isothermal melt crystallization mechanism remained. Linear PES and branched PES all behaved as non-Newtonian fluid; furthermore, the dynamic complex viscosities, loss modulus, and storage modulus exhibited decreased tendency at all studied frequency ranges with increasing side chains content. In addition, the hydrolytic degradation process was slower in branched PES copolymers than in linear PES.In this dissertation, a series of PES-based copolyesters with various structure and properties were prepared, the PES-based copolyesters showed good mechanical properties and adjustable degradation behaviors. This dissertation is helpful in better understanding the relationship between the structures and properties of PES-based copolymers, which will provide reference in modification of other biodegradable polyesters.