Understanding the Reaction of Hydroxy-Terminated Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) Random Copolymers with a Monoisocyanate

This work investigates the reaction kinetics of relatively high molecular weight poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymers containing primary and secondary hydroxyl groups (1°OH and 2°OH) as well as terminal carboxylic acid groups (COOH) with a monoisocyanate. To facilitate their end use in block copolymer synthesis, effects of molecular weight (24–194 kDa), [NCO]/[OHtotal] (1.2–8), and reaction time (4–17 h) were studied. The results show that 1°OH reacted faster than 2°OH, as expected, while the COOH did not react with isocyanate at all under these conditions. Both urethane and allophanate groups were formed. A further reaction of a hydroxy-terminated PHBV (Mn of 27 kDa) with monoisocyanate was undertaken at a ratio of 2.2, with more detailed analysis over time showing the complete reaction of 1°OH and 95 mol % reaction of 2°OH within 4 h at 65 °C. This work is a basis for the potential for controlled PHBV-based block copolymer synthesis.