Molecular Simulation And Experimental Study On The Structure And Glass Transition Behavior Of Polyborosiloxane

In this paper,the cross-linking model of polyboron nanotubes is constructed by computer simulation method and combined with experimental methods,which reveals the preparation principle,structure formation process and material performance characteristics of polyborosiloxane materials.In this study,Materials Studio 2019 software was used to calculate molecular mechanics and molecular dynamics.First,the monomer structure was optimized through different force fields and optimization algorithms,and a force field and optimization algorithm suitable for optimizing the monomer structure were obtained.Second,based on the optimized monomer model,the molecular structure of the polyboron nanotube cross-linking system was molecularly optimized.Modeling,comparative analysis of different B/Si,amorphous network structure model structures formed at different densities,and finally replacing the cross-linking model,different B/Si polyborosiloxanes were prepared and characterized.And confirmed with the simulation results,a breakthrough in the behavior of the pyrolysis process.First,using different force fields and optimization algorithms to optimize the structure and energy of the calculation results of boric acid and trihydroxy monomer monomers,it is called a suitable force field and optimization algorithm for different monomers.Subsequently,a dynamic loop method was used,the functions on the Material Studio software were called using the Perl programming language,and the non-reactive Dreiding potential function was used to successfully model the cross-linked structure.Different densities and different B/Si systems have been cross-linked,and it is called the cross-linking model that can reflect the real situation under corresponding conditions.The results show that the minimum density cross-linking model is difficult to reflect the real continuous network cross-linking model;the cross-linking models with different B/Si highest cross-linking degree do not change significantly;the models with the highest cross-linking degree are mainly Different ring structures are connected together,and it is found that the cylindrical structures are mainly three-and four-membered silicon rings and three-and four-membered mixed rings,and the proportion and number of polar structures show a certain regular change with the change of B/Si ratio;As the B/Si ratio increases,the stack volume of the cross-linked model also decreases continuously,and the mean square displacement of the model decreases continuously as the degree of cross-linking increases.The influencing factors of the degree of crosslinking were investigated,and it was found that the truncation fracture had a significant effect on the degree of crosslinking,and the system density and B/Si ratio had no significant effect on the degree of crosslinking.Based on the free volume theory and step-by-step simulation,we predicted the thermal properties of cross-linking models with different B/Si ratios and cross-linking degrees.The study found that the Tg temperature predicted by the free volume theory,and the Tg temperature calculated by the stepwise simulation and the experimental results were found to be similar,which can provide a basis for simulation and experiment for the free volume theory.It was also found that as the B/Si ratio and the degree of crosslinking increase,the Tg temperature also increases,with the influence of the degree of crosslinking.We prepared polyborosiloxanes with different B/Si ratios by the anhydrous sol-gel method and converted them into a variety of suitable preparation processes.Based on DSC,the Tg temperature of the polysiloxane nanoxerogel was calculated.It is roughly similar to the simulated Tg temperature,and it is found that the quality change of the pyrolysis process is mainly divided into four stages,called possible pyrolysis reactions in different stages,and the pyrolysis products are considered to be Si BOC ceramics.