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Abstract (Summary)
Poly($\beta$-hydroxybutyrate), PHB and the related copolymer poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3HB-co-4HB), are naturally occurring polyesters produced by numerous microorganisms which have attracted much attention in the past decade as potentially commercial biodegradable thermoplastics. Part of the goal of this research is to chemically synthesize PHB and poly(3HB-co-4HB) by the ring-opening polymerization and copolymerization of butyrolactones. The first part of the research focused on the optimization of reaction conditions, modification of alumoxane catalysts and understanding of mechanism for the ring-opening polymerization of (R,S) -$\beta$-butyrolactone, (R,S) -$\beta$-BL. The stereoregular polymerization of (R,S) -propylene oxide (PO) was also studied, which shed a light on the polymerization of (R,S) -$\beta$-BL. In the second part of the research, a copolymer, poly(3HB-co-4HB) was synthesized by copolymerizing (R,S) -$\beta$-BL and $\gamma$-BL. Copolymers with 4-HB contents up to 33 mol% could be prepared depending on the initial ratio of $\beta$- and $\gamma$-BL. The copolymers, which were characterized by $\sp1$H-NMR, $\sp{13}$C-NMR, GPC and DSC. NMR analysis, had a random sequence distribution of 3-HB and 4-HB units. Biodegradation tests showed that the biodegradation rates of the copolymers were higher than that of poly(3-HB) and increased with the increasing contents of 4-HB units. In last part of the research, a biodegradable polyethylene was prepared by copolymerizing ethylene with 2,-methylene-1,3-dioxepane (MDP) at approximately 1,000 psi. The copolymers obtained, poly(MDP-co-Ethylene) were characterized by elemental analysis, IR, $\sp1$H-NMR, $\sp{13}$C-NMR, DSC and GPC. The copolymers were found to contain 2-15 mol% ester group. The copolymer underwent acidic methanolysis and its molecular weights decreased by ten times on average after the methanolysis.
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