Glycerol-based enzymatically synthesized renewable polyesters: Control of molecular weight, degree of branching and functional endgroups

The catalytic specificity of Lipase B from Candida antarctica (CALB) has been exploited to achieve specific terminal groups for the synthesis of glycerol poly(ester)s. This permits the preparation of glycerol-derived macromers able to undergo further reactions/chemical modifications for customization as functional systems and building blocks for polymer synthesis. Poly(glycerol adipate) based macromers with different terminal structures were achieved from the reaction between glycerol and divinyl adipate by varying the stoichiometry (from equimolar to 1.5 and 3.0 excess either of glycerol or divinyl adipate) and amount of catalyst (1 and 3 wt%). In the course of polymerization, transesterification and hydrolysis reactions occur over vinyl functionalities that result in acid endgroups. Thus, the resulting macromers are either terminated with hydroxyl groups and/or acid groups and/or vinyl groups. Therefore, an understanding of how acid functionality appears (from vinyl groups hydrolysis) and its quantification under various conditions may provide an opportunity for the design of synthetic strategies to avoid acid production and obtain the desired structures. Endgroup analysis was carried out using 1H NMR and 13C NMR spectroscopies and MALDI-TOF spectrometry. Mainly linear hydroxyl and vinyl-terminated macromers were obtained with high efficiency without significant hydrolysis of the chain ends (for vinyl terminated).