Molecular Simulation Of Cocondensation Polymerization Process

In recent years, synthetic polymers have evolved rapidly and played an increasingly important role in human life. A lot of theoretical and experimental research about synthetic polymers was carried out. As one of the most important kind of reactions, copolymerization could improve the polymer performance by mixing comonomers. However, due to the complex reaction,inaccurate reaction conditions, time-consuming and high cost of reaction conditions screening,uneasy to characterize the sequence structure, many modified polymers could not produce actual use. Molecular simulation with random characteristics was always used to study polymerization by controlling reactions precisely and visually. This method could compensate the disadvantages of experimental research and promote the theoretical research of polymer science. In our study, the Monte Carlo simulation method was used to study copolycondensation process.Firstly, a homopolycondensation model and a cocondensation polymerization model for producing linear polymers were established for the first time based on the Monte Carlo simulation method. They were compared with the classical theory of Flory's about condensation polymerization and cocondensation theory based on equal reaction center concentration. The simulation results fitted well with the Flory's theory and second-order reaction characteristics.Through the polymerization of the two kinds of monomers with the same reactivity, the results fitted well with the theoretical model, even though the concentration ratios of monomers were very different. It also showed that this MC model was mainly used in the situation that the concentrations of the components would not change with time. Parameter r was used to study more complex cases like the polymerization with different monomer reactivities.Secondly, this model was used to study the influence of monomer reactivities on the average sequence length of polymers in two kinds of situations: one was adding two kinds of monomers with the same quantity, the other one was adding a small amount of comonomers. It could beconcluded that the theory based on the assumption of invariable reactivity center could be applied in the system adding a small amount of comonomers or in the system with similar reactivity of the two monomers. If a large proportion of comonomers were added and the reactivity of the comonomers was greater than that of the monomers, the theoretical prediction showed a large deviation. The the number average length ratio of the two different blocks was close to the feed ratio of the two different monomers, no matter how the reactivity of the comonomer unit changed.However, the block length depended on the reactivity of the monomers. In the micro blending modification system, the comonomer unit tended to disperse in the main chain. The reactivity of the comonomers would not significantly change the block length and apparent reaction kinetics.Finally, the model was used to study the characterization of crystallization and phase separation process of cocondensation polymers in athermal conditions. The results showed that the sequence and structure of the polymers greatly impacted on nucleus, growth and crystal morphology. The increase of the content of copolymer unit would lead to the decrease of crystallinity and the starting temperature of crystallization. While in the equal molar ratio, the increasing of the reactivity of the comonomer unit would lead to the increase of the sequence length, and the morphology of the polymer could change from unable to crystallization to physical gel network structure. This morphology of the micelles formed in the selective solvent was affected by the content of the comonomer unit and sequence structure of the copolymer. A large number of stable small micelles would be obtained with large content of comonomer units, instead large micelles would be obtained. Moreover, the simulation results showed that small amount of comonomer units could inhibit the growth of crystal nuclei and lead to bulk crystals and polymers without high degree of polymerization. When the content of comonomer units was larger than10%, comonomers would inhibit the nucleation and the growth of crystals significantly, which led to a higher degree of polymerization. However, the reactivity of the comonomer had little effect on both the crystallization and polymerization process.