Thermolysis and Methanolysis of Poly(.beta.-hydroxybutyrate): Random Scission Assessed by Statistical Analysis of Molecular Weight Distributions

Abstract

Samples of a bacterial polyester, poly@-hydroxybutyrate), have been degraded thermally as a thin film on a thermocouple-controlled filament at 350 "C. In one series of these thermal experiments a short pyrolysis time (5 s) was used in order to ensure only partial pyrolysis, while in another series of thermal experiments the pyrolysis was allowed to proceed until all the sample had decomposed to volatiles. Samples from the same batch were also degraded in solution by methanolysis under acid conditions, while under reflux at 84 "C. In all cases, the yields and molecular weights of the products were assessed by gas chromatography. The number and weight distributions of the oligomeric products observed have been compared with those predicted statistically on the basis of random scissions. The results show that total thermolysis can be interpreted exclusively in terms of a random chain scission mechanism. However, the partial pyrolysis results are not consistent with random scission statistics; these results imply that there are some kinetically favored scissions occurring near the ends of the molecules. The product distributions from methanolysis are also somewhat inconsistent with those expected on the basis of random scission and may suggest that dimers hydrolyze more readily than higher molecular weight species.

Biofibres, biodegradable polymers and biocomposites: An overview

“…Lehrle and Williams 101) have reported that under certain conditions random chain scission can not be responsible exclusively for the formation of the observed degradation products. In particular, it was shown that primary products are involved in a number of secondary reactions and isomerizations and, indeed, that tetramer is formed principally as a result of such secondary reactions 102) . The two monomer units i. e., 3-hydroxypentanoic acid (trivially known as 3-hydroxyvaleric acid or 3HV) and 3-hydroxybutyric acid (3HB) of PHBV copolymer are shown in Fig.…”

Precise Depolymerization of Poly(3-hydoxybutyrate) by Pyrolysis

“…Lehrle et al reported that the analytical results of partial pyrolysis of PHB showed some deviations from theoretical predictions of random scission statistics (Lehrle et al, 1994(Lehrle et al, , 1995. These deviations were probably due to reactions induced by the end groups.…”

Reprocessability of PHB in extrusion: ATR-FTIR, tensile tests and thermal studies

“…This is an important limitation for processing and consequently, to mechanical recycling. Therefore, there has been a great deal of interest in studying the thermal degradation behavior of PHB and other related poly(hydroxyalkanoate)s [29][30][31][32][33][34][35] . Also studies seeking to improve the thermal stability of PHB by grafting chemicals in PHB chain [33,36] , and adding polymeric additives in PHB matrix [37,38] have been developed.…”