Crotonic acid, degradation product

Moreover, PHB thermally decomposes at temperatures just above its melting point. A short exposure of PHB to temperature near 180°C could induce a severe degradation accompanied by the production of the degraded products of olefinic and carboxylic acid compounds, e.g., crotonic acid and various oligomers through the random chain scission reaction that involves a cis-elimination reaction of/3-CH and a six-member ring transition [16-18]. 

Although crotonic acid, or 2-pentenoic acid from HV comonomer, is the main decomposition product from the biopolymers at low temperature, other degradation products appear under high-temperature pyrolysis conditions. For PHB homopolymer these include propene and carbon dioxide from the breakdown of crotonic acid itself, isocrotonic acid from the obvious reorganization reaction and /3-butyrolactone as a short-lived intermediate that spontaneously decomposes by 0-alkyl scission to propene and carbon dioxide or by O-acyl scission to acetaldehyde and ketene. Similar reactions can be proposed for the comonomer decomposition and some pyrolysis experiments have already been reported. ... 

Hostacoll C, a presumably low-molecular-weight condensate resin of ethyl-enimine, crotonic acid and ethylene glycol, was used in the 1950s as a coating and consolidant for stained glass (Jagers et al., 2000). It degrades to water-removable products. 

In Scheme 9.6, previously reported mechanisms of the thermal degradation of PHB and PHAs are illustrated. Even though many approaches have been taken on the subject of PHB thermal degradation, a clear explanation for the wide variation in value has yet to be provided. Despite this uncertainty, the random jS-elimination scission has been widely held as the exclusive degradation mechanism of PHB based on typical structures of pyrolysis products, i.e., crotonic acid and oligomers with a crotonate end-group [68, 80]. In 2007, an ElcB mechanism proceeding via a-deprotonation by a carboxylate anion to produce the same products was proposed by Kawalec et al. [81]. 

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