Copolymerization Process Characteristics Study Of Poly (Propylene Carbonate)

The CO2 utilization has become a worldwide issue due to the severer green house effect, in which utilizing CO2 as a monomer to produce degradable plastic is a new promising approach. Most relevant literatures focused on the development of new catalyst system, ignoring the study of kinetic, thermo equilibrium, process rheology, etc. The characteristics of this reaction, like extremely sensitive to impurities, gas-liquild-solid multiple phase, wide change in viscosity, are also obstacles in conducting relevant research. Due to lack of these fundanmental data, severe problems arise in the scale-up process in industry and limit the industrialization. To solve these problems, this article focuses on the copolymerization of CO2 and propylene oxide (PO) catalyzed by zinc glutarate, a promising catalyst in application nowadays, and carries out the following researches:Measurement and modeling of the phase behavior of the CO2 and PO. The equilibrium data at temperatures (303.2 K to 353.2 K) suitable for this typical reaction was obtained. A good description of the phase behavior in a wide range of temperatures with the Peng-Robinson equation of state using one-parameter conventional van der Waals mixing rule has been obtained, based on meansured data and literature data. A temperature-dependant bianray interaction parameter kij, was obtained to better predict the equilibrium data at a wide temperature scale (303.2 K-473.2 K).The characterization of the catalysts, the copolymerization product (mixture) and poly (propylene carbonate). The catalyst structure and content was analyzed with infrared spectroscopy (IR), 1H NMR and atomic absorption spectrometer; the copolymerization product was analyzed with IR and 1H NMR to determine the composition; poly (propylene oxide) was analyzed with IR, 1H NMR,13C NMR, gel permeation chromatography (GPC) and thermo gravimetric analyzer (TGA) to determine the structure, molecular weight and its distribution and the thermal stability. Process characteristic study of CO2/PO copolymerization. Effects of stirring speed, catalyst concentration, pressure, reaction time on the yield, catalyst efficiency, copolymer composition, polymer structure, molecular weight and its distribution were analyzed. After a systematic investigation of pressure's effect on the copolymerization, we found that high pressure was not a necessity. High pressure (3.5-5.2 MPa) favored PPC's selectivity and the alternating structure in the polymer chain. However, the PPC's selectivity was slightly improved under high pressures. Under low pressures (0.5-2.6 MPa), the copolymerization rate increased with the increasing pressure due to the CO2 concentration increase, whereas high pressure resulted in the catalyst/epoxide dilution which accounted for the rate decline. Meanwhile all the PPCs prepared under different pressures exhibited high molecular weights and broad distributions, which were determined by the high activity and multiple active sites of the catalyst. Other than the one prepared under 0.5 MPa, all the PPCs possessed a relatively good thermal stability. Considering the higher copolymerization rate and relatively stable properties, the pressure is suggested to be set between 2.6 MPa and 3.5 MPa for the CO2/PO copolymerization. This trend may apply to other catalyst systems while the catalyst differences should be taken into consideration. With the phase equilibrium data of CO2/PO and experiments carried under different pressures and with different catalyst loadings, the kinetic of this reaction was drawn to help prodict the process.By way of the stirring current, the process rheology characteristics of this complex, multiphase system have been studied. The viscosity was very low at the beginning, while at the end it was above 10 Pa·s. Under low and middle pressures, the viscosity increased rapidly while under high pressures, the viscosity increased little.