Synthesis of Itaconate-Based Biopolyesters with Improved Polycondensation Control

Unsaturated biopolyesters synthesized using biomass-derived itaconic acid or dimethyl itaconate offer a greener alternative to petroleum-based polyesters. Despite the volume of research reporting itaconate-based biopolyesters, limited control over side reactions affecting the structure, dispersity, and thermal/mechanical properties limit their adoption. Here, five unsaturated copolyesters were synthesized comparing the effect of diol structure (aliphatic, cyclic, or branched) and Lewis acid catalyst [zinc acetate and dibutyltin oxide (DBTO)] on melt-polymerization. Chromatographic and spectral characterizations revealed superior control by zinc acetate over DBTO with targeted molar masses (3.5–4.5 kg/mol) and narrowed dispersity ( D̵ < 2). Free-radical initiated photocuring biopolyesters catalyzed with zinc acetate provided films with lower glass-transition temperatures for biopolyesters with aliphatic diols ( T g ranging from −35 to −19 °C) versus those with branched or cyclic diols (from 0 to 8 °C). To increase cross-linking, cross-linkers tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate or pentaerythritol tetrakis (3-mercaptopropionate) (PEMP) were added to curing polymer formulations. The highest glass-transition temperatures (62 and 72 °C) were obtained with PEMP, a tetra-functional thiol cross-linker. Unsaturated biopolyesters with improved preservation of the unsaturated moiety and controlled molar-mass distribution enable improved tailoring of the thermal and mechanical properties increasing performance in industrial coating applications.