The Synthesis Of Phenyl Vinyl POSS And Studay Of Its Film Mechanical And Thermal Properties

POSS is the silicon-containing material with-Si-O-Si-structural units.It is used as a modifier to optimize the mechanical properties,thermal stability and dielectric properties of materials due to their unique nanoscale and organic-inorganic hybrid structure.However,with the development of high-tech fields such as aerospace,not only high single performance material is required,but also good comprehensive performance is very important.For example,the thermal protective coating applied for the hypersonic vehicle needs to have good thermal and mechanical properties.This paper is based on major scientific issues and key technologies that constrain the application of POSS as high performance and high value-added materials.In this paper,firstly,the synthetic process of phenyl-vinyl POSS was investigated.Then,the effects of different cage structures and TEOS contents on the thermal and mechanical properties of thermal protective coatings were investigated.Finally,the synthetic process of the thermal protective coating with high thermal stability and good mechanical properties was determined.In this study,phenyl-vinyl POSS was synthesized by fluoride rearrangement reactions using phenyl POSS and vinyl POSS as initial reactant species.And the effects of different solvents,initial reactant species and initial reactant ratio on the synthetic process of phenyl-vinyl POSS were investigated.The structure of the product was characterized by infrared spectroscopy and matrix-assisted laser desorption/ionization time of flight mass spectrometry.When the mass ratio of phenyl POSS:vinyl POSS is15:1,the T₁₀0 product includes Vinyl₁Ph₉POSS.When the mass ratio of phenyl POSS:vinyl POSS is 7:1,the obtained T₁₂ product is Vinyl_xPh_?12-x?POSS?x=1³?.The thermal property of the phenyl-vinyl POSS was analyzed by thermogravimetric analysis.T₁₀Vinyl₁Ph₉POSS has better thermal stability than T₁₂Vinyl_xPh_?12-x?POSS?x=1³?.Furthermore,the thermal stability phenyl-vinyl POSS affected by the proportion of functional groups in the POSS.T₁₀Vinyl₁Ph₉POSS has good thermal stability(T_d5%>500°C).In order to obtain a thermal protective coating with high thermal stability and good mechanical property,firstly,the effects of different cage structures on the thermal stability and mechanical properties of hybrid membranes were investigated.Then different TEOS contents on the thermal stability and mechanical property of hybrid membranes were investigated.The morphology,mechanical property and thermal stability of the hybrid membrane were characterized by atomic force microscopy,nanoindentation,nanoscratch testing and thermogravimetric analysis.In the study of the effects of different cage structures on the thermal stability and mechanical property of hybrid membranes,due to the different cage scale,T₈+T₁₂ phenyl POSS are easy to assemble in the film to form compact structure.The film that T₈+T₁₂ phenyl POSS modified contains fewer defects than other groups.So,it has the biggest hardness?5.28GPa?and the biggest adhesion strength of coating-substrate?2 mN?.Furthermore,it has good thermal stability(T_d5%>550°C).20 wt%TEOS modified phenyl-vinyl POSS based hybrid membrane has the lowest brittleness index?0.37?,the maximum adhesion strength of coating-substrate?6.3 mN?,high hardness?4.46 GPa?,high elastic modulus?12.00 GPa?and good thermal stability(T_d5%>550°C).So,it has the best comprehensive performance.