Study On The Chemical Synthesis Of Poly(3-hydroxybutyrate) And Its Copolymer

Biodegradable plastics have great significances in the field of environment protecting. As one kind of biodegradable plastic, poly(3-hydroxybutyrate) (PHB) have been produced by biological ferment presently. But the price is so high that it can not be used widely. PHB synthesized by chemical method, however, will reduce the cost and improve the property by adjusting polymer's structure. The purpose of this paper is to study the chemical synthesis route of producing PHB.In this paper, ethyl 3-hydroxybutyrate and 3-hydroxybutyric acid were firstly used to synthesize PHB by means of condensation polymerization respectively. The product was characterized by 1H NMR and the results showed that crotonic acid was mixed in the reactant resulting in the lower molecular weight of resultant PHB. So PHB with high molecular weight can not be synthesized in this way.In this paper, crotonic acid was also chosen as raw material to synthesize PHB. Crotonic acid was firstly reacted with HBr to synthesize 3-bromobutyric acid. Thenβ-butyrolactone was obtained by ring-closing reaction of 3-bromobutyric acid. 1H NMR and FTIR measurement demonstrated the formation ofβ-butyrolactone. Based on these, anionic ring-opening polymerization ofβ-butyrolactone was performed using tetrabutylammonium carboxylates(TBA acetate) as initiator. The influences of reaction time, reaction temperature and polymerization method on molecular weight of PHB were studied. 1H NMR, 13C NMR and ESI-MS were utilized to identify the structure of PHB obtained. The analysis of 13C NMR indicated that the configuration of PHB was atactic and TBA acetate had no capability of controlling configuration of the repeating unit.TBA acetate was also used to initiate the anionic ring-opening copolymerization ofβ-butyrolactone and L-lactide. 1H NMR, 13C NMR and ESI-MS were also utilized to identify the structure of copolymer. The analysis of 1H NMR showed that the ring-opening reaction of L-lactide occurred more easily thanβ-butyrolactone. 13C NMR indicated that the repeating unit of copolymer did not follow the Bernoullian statistic.