Study On The Preparation Of Biodegradable Poly(β-hydroxyalkanoate)s

With the rapid development of science and technology,the economical and societal issues associated with the depletion of fossil feedstocks and severe accumulation of non-degradable plastics in nature have pushed the increasing efforts towards the development of bio-degradable polymers.During the last decades,polyhydroxyalkanoates（PHAs）have received intense interest that found a variety of applications in packaging,agriculture,biomedical and pharmaceutical fields.PHAs are a class of biocompatible,biodegradable materials that are widely used in daily life.Carbon monoxide（CO）is an abundant carbon resource,while epoxides are important fundamental and industrial chemicals,and the direct carbonylative polymerization of epoxides for the sysnthesis of PHAs has received intense interest in academia and industry,moreover,this polymerization features with atom economy.Though much progress has made in this field,this reaction has still suffered from low activity and selectivity,only affording PHAs with limited M_n values,therefore,a new catalyst design concept is urgently needed to solve the current problems.In 1994,Drent has discovered that Co₂（CO）₈ and 3-hydroxypyridine can catalyze carbonylative polymerization of propylene oxide for the preparation of poly（3-hydroxybutyrate）s,while their M_n values were rather limited（<2000 g/mol）.In 2000,Coates has discovered that salph-metal complexes/Co₂（CO）₈（salph=N,N?-o-phenylenebis（3,5-di-tert-butylsalicylideneimine））was efficient towards ring-expansive carbonylation of epoxides toβ-lactone.Therefore,the bifunctional complexes based on salph-metal centers with organic base are designed for the selective carbonylative polymerization of epoxides for the synthesis of polyhydroxyalkanoates materials.Furthermore,we have developed a type ofβ-lactone fused with a five membered ring fusion atαandβ-positions,3,6-dioxabicyclo[3.2.0]heptan-7-one（β-COL）,from the ring-expansive carbonylation of 3,6-dioxabicyclo[3.1.0]hexane（COPO）,can be produced by the bifunctional catalysts and metal-tetraphenylporphyrin complexes.A variety of catalyst systems,including organo-metallic（rare-earth metal complexes）and organic catalysts are used for ring-opening polymerization ofβ-COL.By using NMR investigation,it is discovered that the regio-ring-opening reaction（O-acyl versus O-alkyl cleavage）during the ring opening polymerization ofβ-COL significantly impacts thermal stability of the resultant PHAs.