Poly(glycerol-sebacate) bioelastomers-kinetics of step-growth reactions using Fourier Transform (FT)-Raman spectroscopy

Kinetic studies of the esterification of glycerol (G) and sebacic acid (SA) at three molar ratios (0.6, 0.8, 1.0) and at three temperatures (120, 130, 140°C) to form poly(glycerol-sebacate) were performed and assessed using FT-Raman spectroscopy. The quantitative changes in the concentrations of carboxylic acid and ester groups within the forming bioelastomer were measured and the chemical rate constants (k) determined from the kinetic scheme were first-order, with respect to sebacic acid concentration. Increasing the reaction temperature by 20°C is noted to increase the chemical rate constant (k) by a factor of up to 4.5 and the total extent of conversion at early times for the molar ratios investigated. The activation energy (E a ) and the pre-exponential factor (A 0 ) for these three stoichiometric ratios were calculated, which varied in accordance with the average functionality of the system. Under isothermal conditions, the chemical rate constant remained unchanged with an increase in the extent of the reaction (α) until a spontaneous transition resulted in the shift in the mechanism from kinetics to diffusion controlled. The Young's moduli of the PGS polymers were found to depend primarily on the average functionality of the system and the curing period. This investigation confirms the reaction mechanism for PGS polymer synthesis and shows the flexibility afforded to PGS properties and reaction times through varying the stoichiometric ratios of glycerol to sebacic acid.