Preparation And Thermal Properties Analysis Of Polyborosiloxane

Organopolysiloxane whose main chain is inorganic Si-O-Si structure has excellent high temperature performance,thermal oxidation stability and radiation resistance.Because of its special properties,it is used as the preferred materials in the aerospace,electronics,chemical industry and other fields.With the development of science and technology and the needs of modern aerospace materials,higher requirements are placed on the high temperature resistance and damping properties of materials.Therefore,it is necessary to design the polysiloxane structure.The introduction of high-temperature-resistant heteroatoms significantly improves the mechanical properties and thermal properties of the material.Therefore,the research on the silicone polymers containing heteroatoms is particularly important.In this paper,a series of polyborosiloxanes(PBS)with different structures were prepared by condensation reaction,Piers-Rubinsztajn reaction,and equilibrium reaction using phenylboronic acid as the boron source,and polyborosiloxane elastomers were prepared by vulcanization.Boron atoms enter the main chain of the molecule to form Si-O-B bonds with higher bond energy,which improves the thermal stability of the material.In addition,in the PBS structure,the boron atom can form a weak boron/oxygen bond interaction with the oxygen atom in the adjacent molecular chain,which improves the interaction between the molecules.The boron element also has a stable free radical Effect,increasing the thermal stability of the polymer The relationship between PBS thermal stability,dynamic mechanical properties and molecular microstructure were explored,this paper mainly carried out the following research work(1)A series of PBS with different structures were synthesized by condensation reaction with phenylboronic acid and hydroxyl terminated polysiloxane with different structures as raw materials.The structure of PBS was characterized and analyzed by infrared,nuclear magnetic,rotational viscometer and other analytical test methods.The research results showed that the PBS has a high molecular weight and good stability when the reaction temperature is 160? and the reaction time is 3 h;From the thermogravimetric analysis results,compared with the hydroxyl-terminated polysiloxane,the thermal stability of PBS with different structures was improved.Among them,the thermal stability of polyborosiloxane(PBS-1)obtained by condensation of 2000 mPa·s hydroxyl-terminated polydimethylsiloxane and phenylboronic acid was the most obvious,and its 5%weight loss temperature and 10%weightlessness temperature increased by more than 25?.(2)The PBS elastomers were prepared by vulcanizing PBS with different structures,and the structure and properties of PBS elastomers with different structures were analyzed in detail.The Piers-Rubinsztajn method was used to synthesize PBS,and the effects of Piers-Rubinsztajn method and condensation method on the thermal stability of PBS were investigated.It was confirmed PBS was successfully synthesized by P-R reaction.Through comparative analysis of thermal performance,the thermal stability of polyborosiloxane prepared by P-R reaction was poor.Compared with methyl phenyl silicone rubber(PMPS),the thermal degradation range of methyl phenyl polyborosiloxane rubber(PBS'-4)moved to the higher temperature,and the maximum thermal weight loss temperature was 539?.(3)Using high molecular weight methylphenyl polysiloxane,diphenyl polysiloxane and phenylboronic acid as raw materials,methyl phenyl polyborosiloxane and diphenyl polyborosiloxane were synthesized by equilibrium polymerization.The effects of different B:Si ratios on the molecular chain structure,mechanical properties and thermal properties of PMPBS and PDPBS were discussed.The results showed that the thermal performance of PMPBS and PDPBS is the most obvious when B:Si is 1:150 and 1:300 respectively.By analyzing the influence of the condensation method and the equilibrium polymerization method on the thermal properties of polyborosiloxane,it was known that the polyborosiloxane prepared by the condensation method has the best thermal stability.