Synthesis And Properties Of CO₂Terpolymer

Though carbon dioxide (CO2) is the main greenhouse gas, it is an abundant,inexpensive, and renewable carbon resource. Therefore, the catalytic transformationof CO2into biodegradable poly(propylene carbonate)(PPC) by alternatingcopolymerization with propylene oxide (PO) has drawn much attention in view ofeconomic and environmental benefits arising from application of an easily availablerenewable carbon resource, reduction of “greenhouse gas pollution” and “whitepollution” caused by barely degradable polyolefins after use.Great efforts were devoted to developing highly active catalysts in the pastseveral decades. PPC now has been commercialized. It possesses excellent adhesion,transparency and low permeability for oxygen and water, and it burns gently in aironly producing CO2and water. So PPC has a wide range of applications such asbinders, biological medicine and packing material. However, the practical applicationof PPC has been limited by its poor thermal stability and mechanical performance.Therefore, many approaches have been developed to improve the thermal andmechanical properties of PPC, such as physical blending, terpolymerization andcross-linking. Although several attempts have been achieved, it is now very hard tomodify the material profile of PPC fitting for existing applications. In fact, physicalblending often meets with an incompatibility between the two phases of PPC andother polymers, organic compounds or inorganic fillers. In addition, the conventionalterpolymerization requires large quantities of third comonomer, which isunfavorablefor biodegradation or cost and sometimes high Tgof the terpolymer makes it brittle;Unfortunately, the reported crosslinking strategies generally require two stepsincluding incorporation of double bonds into PPC chains and post-treatment withradical initiators, which is not economical. Based on this, developing and designing agreen economy synthesis aliphatic polycarbonate with excellent properties method isthe hot issues of current research.The contributions of this dissertation include the following three aspects,PPCKH/SiO2s, PPCIAns and PPCLAs were synthesized by adding the third monomerKH-560, IAn and L-LA in the copolymerization of CO2and PO, respectively. Moreover, their thermal stability, mechanical properties and degradation propertiesproperties were also investigated.First, terpolymerization of carbon dioxide (CO2) with propylene oxide (PO) and3-glycidyloxypropyltrimethoxysilane（KH-560）was successfully carried out usingzinc glutarate catalyst (ZnGA). Consequently giving a new type of polycarbonate(PPCKH). PPCKH/SiO2composites were prepared from PPCKH andtetraethoxysilane (TEOS) by sol-gel process. As a result, the introduction of KH-560lead to PPCKHs molecular weight and yield were reduced, but the molecular weightdistribution of PPCKH gained were narrow. And the PPCKH/SiO2thermaldecomposition temperature(Td,-5%) and the maximum thermal decompositiontemperature(Td,max) is higher than the PPC. Especially, Td,-5%and Td,maxofPPCKH/SiO220(262.3and294.1℃) were64.4and53.0℃, which are higher thanthose of PPC (197.9and241.4℃), respectively, indicating that thermal stability ofPPC can be greatly improved by sol-gel technology introduction of SiO2in thePPCKH.Second, cross-linkable aliphatic polycarbonate PPCIAn was easily prepared byterpolymerization of CO2, PO and IAn using ZnGA catalyst, The results show that theaddition of IAn improves the product yields and molecular weights obviously. Inparticular, the number average molecular weights and product yields of PPCIAn4canbe achieve101000g/mol and8036.3g/(mol of Zn). The results of the thermal stabilityand mechanical properties tests showed the thermal stability and mechanicalproperties of PPCIAn are better than those of PPC. Especially, the Tgof PPCIAn4canbe up to39.7℃, maximum tensile strength can reach27.5MPa, this is much higherthan those of PPC(34.9℃and4.7MPa). In addition, the degradability of PPCIAn4was determined in the phosphate buffer solution (PBS) of pH7.4at37℃for10weeks. PPCIAn4exhibit high degradability compared with PPC. After10weeks, theweight loss increased up to28.28%, which was significantly higher than that of PPCof4.58%and the results further confirmed by SEM.Finally, PPCLA can be easily obtained by L-LA addition in PO/CO2copolymerization catalyzed by zinc glutarate. The results indicated that the yield andmolecular weights of PPCLA increases with increasing of L-LA monomer molar content in the copolymerization, the highest yield and the number average molecularweights of PPCLA4was66.1g/g catalyst and120000g/mol. This means that theaddition of L-LA improves the product yields and molecular weights obviously. Theresults of thermal and mechanical properties test of PPCLAs indicated the thermaldecomposition temperature and the maximum thermal decomposition temperature ofPPCLA are higher than those of PPC and gradually increasing with the increasing ofL-LA content. Especially, the thermal decomposition temperature and the maximumthermal decomposition temperature of PPCLA4rise to the maximum of260.1℃and281.4℃, respectively. PPCLAs exhibit high mechanical performance compared withPPC, maximum tensile strength of PPCLA4was42.86MPa. Moreover, degradationbehavior of the PPC and PPCLA4was examined by the buffer solution immersiontests. The results showed that the weight loss and the water sorption of PPCLA4arehigher than those of PPC.