| There has been a growing interest on the polymers having the properties of biodegradability, biocompatibility and low toxicity to cope with the serious environmental problems and medical demands. Aliphatic polyesters and polycarbonates belong to these materials with expecting uses as drug delivery medium, surgical sutures, body implant materials, cell culture substrate, agricultural membranes and so forth. However, only a few catalysts (such like Sn(Oct)2) have been studied to synthesize medical-use materials with debating mechanisms. In this dissertation, two series of rare earth initiators: rare earth tri(2,6-di-tert-butyl-4-methylphenolate) and rare earth calixarene complex have been developed to ring-opening polymerize 2,2-dimethyltrimethylene carbonate (DTC), trimethylene carbonate (TMC) and s-caprolactone (CL) at mild conditions. Both the polymerization features and mechanisms are discussed in details.Monte Carlo method is a powerful tool in computational chemistry to investigate polymerization mechanisms and kinetic behaviors at the molecular level. Theoretically speaking, it can handle all kinds of polymerization systems with presumed mechanisms, intimating every occurrence of microcosmic species and the structure of every polymer chain. A Monte Carlo algorithm for multi-dispersive copolymerization system has been established and successfully used in the copolymerization of DTC with CL. Monte Carlo method has been firstly applied to simulate the polymerization systems catalyzed by rare earth compounds, including the gas phase polymerization of 1,3-butadiene and the high viscous bulk polymerization system of styrene, by which the polymerization mechanisms and kinetic processes are fully discussed.Rare earth tris(2,6-di-tert-butyl-4-methylphenolate) initiated polymerizations of DTC, TMC and CL. Rare earth tris(2,6-di-tert-butyl-4-methylphenolate) (Ln(OAr)3, Ln=La,Nd,Y,Dy,Er) was firstly studied in the polymerizations of cyclic carbonates and lactones. Ln(OAr)3 was found active in initiating polymerizations of DTC, TMC and CL. The efficiency of DTC polymerization initiated by La(OAr)3 was 492kgPDTC-mol-1La-hr-1. Homo- and copolymerizations of DTC, TMC and CL were carried out in mild conditions, achieving high conversions (>90%) in 30min at room temperature. The molecular weights of obtained PDTC and PCL were 25.4 104 and21.5 l04, respectively. No ether unit, no rare earth metal and no 2,6-di-tert-butyl-4-methylphenol were found in (co)polymers.Random copolymerization of DTC with TMC was performed by the initiator of La(OAr)3. Only a Tg of -8.3 was observed for P(DTC-ran-TMC) in the second DSC heating scan, higher than PTMC's Tg of -27.TC, and no Tm at the range of 110~130 for PDTC was found.Copolymerization of DTC with CL initiated by Ln(OAr)3 exhibited living features, producing block and random copolymers. The molecular weight and composition of P(DTC-ran-CL) could be controlled by two different ways: controlling polymerization time and total conversion with fixed feeding concentrations of monomers; or controlling co-monomers feeding ratio and processing high conversion polymerization. The reactivity ratios of DTC and CL were measured as 13.43 and 0.20, respectively. New thermal behaviors of P(DTC-ran-CL) differed from those of the two homopolymers. In the second heating scan of DSC, Tms of the random copolymers (DTC%>50%) was disappeared, and a Tg from -33.8 to -7.5癈 were detected instead, which indicates the elastic polymer.The polymerization mechanisms of DTC, TMC and CL initiated by Ln(OAr)3 were fully studied for the first time, and proved to be a "coordination insertion anionic mechanism". Monomer coordinated to rare earth metal on the carbonyl group, and opened ring via acyl-oxygen bond cleavage, forming a growing chain. The following monomer repeated these steps to insert into the Ln-0 bond in propagation process. The aryl carbonate end group of growing chain was replaced by alcohol in termination (or precipitation) resulting alkyl carbonate end...
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