Study On The Ring-Opening Polymerization Of Ethylene Oxide And Propylene Oxide

With the rapid development of science and technology, there has been a growing interest in the polyethers (primarily homopolymers and copolymers of ethylene oxide and propylene oxide), which have the properties of excellent surface activity, flexibleness of HLB and low toxicity to form a wide variety of polyether series. In this dissertation, the ring-opening polymerization mechanism of ethylene oxide and propylene oxide, the polymerization kinetics and the properties of polyethers are studied using various methods to develop high quality polymerization products and improve the alkoxylation process.Firstly, quantum chemical methods are employed to investigate the mechanism of ring-opening polymerization of ethylene oxide and propylene oxide. By analysis of their frontier orbitals, the reasonability of the cationic and anionic polymerization mechanism of ethylene oxide and propylene oxide is confirmed theoretically. Furthermore, the reaction path of alkoxylation process and the activation energies of respective elementary reactions are studied by B3LYP/6-31G+(d) and HF/6-31G+(d) methods, the results show that the anionic ring-opening polymerization of ethylene oxide proceeds by nucleophilic attack of the primary alcohol propagating anion on monomer, the cationic ring-opening polymerization of ethylene oxide proceeds by nucleophilic attack of monomer on the tertiary oxonium ion and the anionic ring-opening polymerization of propylene oxide proceeds by nucleophilic attack of the secondary alcohol propagating anion on monomer. Calculation results could explain the experimental facts satisfactorily.The polymerization kinetics of ethylene oxide and propylene oxide is studied from the microscopic and macroscopic aspects. The theoretical product distribution is deduced with full consideration of the initiation, propagation, chain transfer and proton exchange reactions, and the most widely used theoretical distribution models, Flory and W-N-G, are the reduction of this distribution. The mass transfer and kineticsin alkoxylation spray tower loop reactors are studied, whereafter a copolymerization kinetic model of allyl polyether in alkoxylation spray tower loop reactors is established based on the copolymerization mechanism. The kinetic and equilibrium constants of the described model are determined by regression analysis of the experimental data.The Monte Carlo simulation is employed to validate the copolymerization of ethylene oxide and propylene oxide following the first order Markov model and the sequence distributions of monomer units in copolymers are illustrated by graphs according to Monte Carlo simulation. A new algorithm based on the Monte Carlo method is presented to determine the reactivity ratios, i.e., the reactivity ratios are obtained by comparison of the data simulated from random simulation of chain propagation of copolymerization with the experimental data. Moreover, the alkoxylation reaction kinetics is investigated by the Monte Carlo method. These results of simulation are in good agreement with the experiment.The thermal degradation kinetic parameters are calculated from the TG-DTG curves of polyethers, and the most probable mechanism functions are obtained by the universal integral and differerntial equation methods. The thermal stability of polyethers is investigated by the thermal degradation temperature and the thermal lifetime equations, and the effect of thermal atmosphere, copolyether types, initiator, monomer units' ratios and molecular weight on the thermal stability is revealed. Moreover, the quantum chemical method is employed to calculate the molecular parameters of polyether model compounds and the degradation mechanism of polyether is analyzed theoretically. Based on the identification of intermediates and products of polyether thermal degradation by GPC and NMR, the thermal degradation scheme is proposed, i.e., the thermal degradation proceeds through a random bond cleavage of C-0 and C-C of polyether backbone chain while the thermal oxidative degradation proceeds through a complicated radical bond cleavage of polyether peroxide.Finally, the surface activity of dodecyl and tridecyl block copolyether nonionicsurfactants (RPE) is studied. A linear decrease of ln[CMC] vs the number of oxypropylene units in the copolymer molecule is observed. Furthermore, the penetrating quality of RPE block copolyether is studied and the effect of initiator structures and monomer units' ratios is revealed.As far as know, the above mentioned results concerned the research on the mechanism of ring-opening polymerization by quantum chemical methods, the simulation of the copolymerization by Monte Carlo method, the research on the thermal degradation (kinetics, degradation temperature and lifetime equations) of polyethers by TG-DTG method have not been seen in the literature.