Preparation And Performance Of POSS Modified Polysiloxane Materials

Polysiloxane is widely used in petrochemical,aerospace,electronic appliances,pharmaceutical industry and other fields due to its excellent properties,and has become an indispensable high-tech material at present.With the vigorous development of the green economy,recyclable smart materials have attracted widespread attention.In this paper,through the two methods of hydrosilylation and mercapto-olefin click chemistry,heptaphenyl monosilsesquioxane(Si-H POSS)and heptaisobutyl monomercaptopropyl silsesquioxane(SH-POSS)were grafted onto the side chain of the linear polymethyl vinyl siloxane to prepare a series of silicone materials with excellent properties,while exploring the effects of different grafting conditions on their properties.The main work includes the following several aspects:(1)Four kinds of high vinyl content polymethylvinylsiloxanes(PMVS)with different molecular weights were synthesized by the method of alkali-catalyzed anionic ring-opening polymerization of cyclosiloxane.The PMVS synthesized by this method has a higher molecular weight,the highest Mw can reach 491710.(2)The monofunctional heptaphenyl monohydrogen POSS(Si-H POSS)was synthesized through the "coner-cap" reaction,and the Si-H POSS was grafted onto the PMVS's side chain by the hydrosilylation reaction between Si-H and C=C.There was a series of soluble and transparent silicone elastomer PMVS-HP has been prepared.At the same time,we studied the effects of different molecular weight of the PMVS and different POSS loadings on the glass transition temperature(Tg),thermal properties and mechanical properties of the obtained samples.Experimental and test results showed that the introduction of POSS can significantly improve the Tg and thermal stability of the PMVS,and the temperature at 5%weight loss can be increased to 508?.While,the mechanical properties are increased with the increase of PMVS's molecular weight and POSS content.The tensile strength of the sample is up to 5.95 MPa,and the elongation at break is up to 711.45%.(3)The heptaisobutyl monomercaptopropyl POSS(SH-POSS)was grafted onto the side chain of the PMVS efficiently and concisely through click chemistry to obtain the modified polymer PMVS-SP.We explored the effect of grafting different POSS on the materials obtained,and the experimental results showed that PMVS-SP is a thermoplastic silicone resin,which can be recycled through melting or dissolution.At the same time,the influence of the molecular weight of the PMVS and the content of SH-POSS on the performance of the PMVS-SP was studied.The results showed that grafting SH-POSS can make the material get a higher glass transition temperature,and it's Tg increases with the increase of POSS content,the highest one can reach 76.4?.Furthermore,as the POSS content increases,the material gradually become brittle,but the tensile strength will increase.