Tailoring degree of esterification and branching of poly(glycerol sebacate) by energy efficient microwave irradiation

Poly(glycerol sebacate) (PGS) is known as an exciting biomaterial owing to its tunable mechanical properties and controllable degradation rate. However, it is always challenging to control these properties. In this study, we have proposed a solvent-based system to provide a better control of reaction temperature in a microwave cavity, which can minimize evaporation of monomers, and water was collected to analyse the degree of esterification. Pre-PGSs with varied degrees of esterification were prepared using both single mode and multimode microwave cavity irradiation (MI) in this solvent-based reaction system. For a similar degree of esterification of pre-PGSs, the reaction time was almost halved with a better control on mechanical properties by single mode MI compared to multimode MI. Furthermore, the single mode MI approach was compared with the conventional heating (CH) approach. The mechanical properties and degradation rate of PGSs can be controlled readily by using the single mode MI approach compared to CH, which are crucial for their application as a biomaterial. It has been found that the single mode MI not only accelerates the pre-polymerisation process rate by six times, but also speeds up the curing time to the same extent. The Young's modulus of PGSs prepared by single mode MI is increased from 0.77 to 3.14 MPa when the degree of esterification is 66.82%, which is 50% higher than that reported in the literature. Furthermore, PGS using a highly branched pre-PGS prepared by the single mode MI method has a large degree of flexibility. It can achieve a much higher Young's modulus than that obtained by CH with a short curing time (<10 hours). In addition, the residual mass of PGSs prepared by single mode MI is varied from 78.54% to 92.96% compared to the CH method that ranges from 84.24% to 93.31%. Thus, these highly branched PGSs produced by single mode MI also show a wider degradation window (approximately 59% higher degree of flexibility than the CH method), which is found to be highly dependent on the degree of esterification and curing time of the pre-polymer, and controlled by branching.