Thermal degradation behavior of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate

Abstract

The thermal degradation behavior of poly[(R)-3-hydroxybutyrate-co-16 mol%-4-hydroxybutyrate] (P(3HB-co-16 mol%-4HB)) was investigated based on spectroscopic analysis of its pyrolyzates and two kinetic modeling approaches. Pyrolyzate analysis revealed that trans-crotonic acid, cis-crotonic acid, γ-butyrolactone, and their oligomers (dimers and trimers) were produced following thermal degradation of P(3HB-co-16 mol%-4HB). The kinetic analyses confirmed that the thermal degradation behavior of this copolymer changed depending on the time and/or temperature parameters. Specifically, this degradation process proceeded in at least two steps, (i) initial random degradation and (ii) subsequent 0th-order weight loss, which indicated unzipping degradation of the 3HB units. Based on 13C NMR and two-dimensional NMR methods, it was determined that the unzipping degradation of 3HB units starting from the chain end may stop or volatilize an oligomer when the reaction reaches a 4HB unit randomly present in the copolymer.