Molecular Dynamics Simulation And Experimental Verification Of Side Groups'Effects In Linear Polysioxanes

In this paper,based on the molecular dynamics(MD)method,two new functionalized linear polysiloxanes were designed.The MIPOSS and the NALC were grafted on the side groups of the polysiloxanes,respectively.Both the designed functionalized polysiloxanes had good recyclable repetitive molding properties and were verified by experiments.Specific research works were as follows:(1)Based on MD simulation method,the glass transition temperature(Tg)of the modified linear polysiloxanes with different molecular weight was studied.The results showed that the entanglement molecular weight of the polymers was about 8000(the degree of polymerization was about 50),and the specific volume,free volume fraction,cohesive energy density and mean square displacement function of the polymers all had mutations during the glass transition process,which could be used to accurately simulate the Tg of the polymers.(2)The MIPOSS with different molar content was grafted on the side groups of linear polysiloxane molecules.The flexibility of modified linear polysiloxane molecular chains was effectively controlled by the steric hindrance effect of the MIPOSS.The combination of MD simulation and experiment shows that there was a functional relationship between the Tg of the modified polysiloxanes and the grafting rate of MIPOSS.The grafting MIPOSS modification affected the micro-structure of the systems,and the free volume fraction of the modified polysiloxanes were smaller than that of the unmodified polysiloxanes.The MIPOSS made the cohesive energy density of the modified polysiloxanes increase,the free movement of the molecular chains became more difficult,and the macroscopic mechanical properties of the materials were significantly enhanced.(3)The NALC with different molar content was grafted on the side groups of linear polysiloxane molecules.Due to the existence of amide groups and carboxyl groups in the NALC,hydrogen bonds were easily formed between amide groups,and a large number of reversible hydrogen bond crosslinking networks could be formed between functional linear polysiloxane molecular chains.The combination of MD simulation and experiment shows that by controlling the grafting rate of the NALC and the healing temperature,the materials had good recyclable repeated molding performance and the self-healing efficiency could be controlled.