| Organo polysiloxane is widely used since its excellent heat resistance, weatherability, electrical insulation properties.While thermal aging process becomes apparent impact on the structure and properties of the material in using for long time, the crosslinking reaction and ceramic products caused by aging process get the application. Thus thermal degradation and aging behavior of organopolysiloxane is one of the hot topics people have been studing. Investigating the aging mechanism can provide the relationship of the molecular structure, composition, thermal stability and thermal chemistry for the use, store and structural design of the material. In this paper, vinyl polysiloxane and a variety of alkyl polysiloxanes were synthesized, and then the aging process of these polymers in various gas atmosphere was discussed, specific work as follows: 1. Octavinyl POSS, vinyl silicone resin, n-propyl, n-hexyl, n-octyl silicone resin were synthesized from a variety of alkoxysilanes, and characterized by FT-IR,1HNMR,29SiNMR, GPC, phase contrast microscope, etc.The condensation rate of alkoxy in the raw monomers was calculated using ’HNMR and29SiNMR, only to get the consistent result, which showed that the steric barrier of alkyl chain combined with silicon would not affect condensation of trimethoxysilane monomers. On the contrary, the steric barrier would hinder the condensation of triethoxysilane monomers.Theoretical analysis and calculation of the peak integral of infrared areas verified that structure/atactic structure decreased with the growth of alkyl chains in cyclohexane solvent.2. The thermal oxidative aging process of octavinyl-polyhedral oligomeric silsesquioxane (OVPOSS) heated at180℃in the N2atmosphere with low oxygen concentration was investigated.1H NMR,13C NMR,29Si NMR were used to analyze the molecular structure before and after this process, while FTIR, MALDI-TOF, ESR, TG-IR, DSC were used to monitor the changes of characteristic groups, molecular weight, active species, mass loss and enthalpy. The conclusion was drawn that free-radical polymerization exists in thermal oxidative aging process of OVPOSS at low temperature (180℃) in the N2atmosphere of with low oxygen concentration. This research may enrich the thermal oxidative aging theory of polyvinylsiloxane.3. Comparison of the aging behavior of the vinyl silicone resin and other alkyl silicone resin in N2atmosphere using’HNMR,29SiNMR, TG, DSC and other methods showed that the d-pp conjugative effect between silicon and vinyl facilitated the fracture of Si-OR bond and the increase of O atom s electron density, only to make it easier to attack the Si atom of another molecule.So the thermal condensation of vinyl silicone resin was easier than alkyl silicone resin.This section, together with thermal oxidative aging process, stated vinyl was a special group either to its free-radical polymerization or to promote the reaction of other groups in the molecules.It provided the method of thermal condensation of silicone resin without any initiators, which is of great significance in the store, use, molecular structure design and choice of curing process.4. Thermal oxidative aging research of n-octyl silicone resin in air atmosphere using FT-IR,29SiNMR,TG-DSC-IR showed that the organic group was oxidized to carbonyl compounds like aldehyde group, with the residue of SiO2left.The content of silicon in the resin would not change during thermal aging process.The total process contained two course by TG-DSC-IR machine, with the highest value of the rate of heat loss at320℃and450℃. IR absorption of the volatiles displayed many alkyl groups, and even olefinic compound during the second stage, with CO2, H2O, a small amount of Si-H, ether, aldehyde and other substances.Finally we presented the generation mechanism of each product above. |
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