Effect of enzymatic versus titanium dioxide/silicon dioxide catalyst on crystal structure of 'green' poly[(butylene succinate)-co-(dilinoleic succinate)] copolymers

Focusing on an eco-friendly approach, biodegradable poly(butylene succinate-co-dilinoleic succinate) (PBS-DLS) copolymers with 70:30 (wt%) ratio of hard to soft segments were successfully synthesized via different processes and catalytic systems. In this approach, biobased succinate was polymerized with renewable 1,4 – butanediol and dimer linoleic diol to obtain “green” copolyesters as sustainable alternative to petroleum-based materials. In the first procedure, two-step synthesis in diphenyl ether was performed using Candida antarctica lipase B (CAL-B) as a biocatalyst. Second material was produced via two-step melt polycondensation with the presence of heterogeneous titanium dioxide/silicone dioxide (C-94) catalyst. Obtained PBS-DLS copolyesters were further characterized in regard to their number average molecular weight, chemical structure, thermal transition temperatures and crystallization behavior. Here, a digital holographic microscopy has been used to study the crystallization behavior of synthesized segmented copolyesters for the first time. Using this technique, it was possible to reveal the twisting of crystalline regions in formed spherulites and observe the differences in crystallization behavior of copolyesters depending from the type of catalyst. Structural characterization indicated random and blocky structure of copolymers depending form the type of catalyst. The number average molecular weight (M_n) was noticeable higher in case of PBS-DLS 70:30 copolymer catalyzed using C-94 catalyst than PBS-DLS 70:30 synthesized with use of CAL-B. However, the degree of crystallinity was lower for polymer catalyzed with heterogeneous catalyst. Furthermore, DSC thermal analysis revealed that synthesized copolyesters exhibit low glass transition temperature as well as high melting point which is typical for thermoplastic elastomers.