Preparation Of Functionalized POSS And Its Application Study Of Modified Liquid Silicone Rubber

Two-component additive liquid silicone rubber is mainly based on vinyl silicone oil as the base polymer,hydrogen-containing silicone oil as the cross-linking agent,and auxiliary addition of reinforcing filler.Under the action of catalyst(Pt catalyst),an elastomer with a three-dimensional network cross-linked structure formed by the hydrosilylation reaction.It has the advantages of rapid vulcanization,deep vulcanization and no deformation during vulcanization,and is widely used in medical and health fields.As we all know,silicone rubber has poor mechanical properties due to its disadvantage of low cohesive energy density,and silicone rubber without reinforcement or modification is difficult to meet the needs of actual production and application.Now a days,physical compounding or chemical modification is commonly used to improve the mechanical properties of silicone rubber.Polyhedral oligomeric silsesquioxanes(POSS)is mainly an organic-inorganic hybrid with a three-dimensional network structure composed of the Si-O-Si backbone,which not only gives it the machinability and toughness of organic materials,but also makes it retain the oxidation resistance,heat resistance and good mechanical properties of inorganic materials.POSS has a nanostructure with a diameter range of 1 to 3 nm,and can be considered as modified silica particles.As a modified organic-inorganic hybrid material,POSS can be used as a nano-filler or cross-linking agent.In this paper,we explored the hydrolysis-condensation reaction of ethyl orthosilicate(TEOS)catalyzed by Me₄NOH?5H₂O using nuclear magnetic resonance silica spectroscopy(²⁹Si-NMR),hydrogen-containing POSS(H-POSS),vinyl POSS(Vi-POSS),and methyl POSS(Me-POSS)were prepared by the silicate anion method firstly.H-POSS as precursors,two types of viscous liquid POSS(MMA-POSS and MA-POSS)were prepared by the functional group conversion method using silica-hydrogen addition reaction,respectively.Finally,the two-component liquid silicone rubbers were modified by physical blending or chemical grafting,and the effects of POSS on the thermal stability and mechanical properties of the silicone rubber composites were investigated in detail.This thesis focuses on the following research.(1)The hydrolysis-condensation products of ethyl orthosilicate(TEOS)and tetramethylammonium hydroxide pentahydrate(Me₄NOH?5H₂O)in different ratios were specifically analyzed by ²⁹Si-NMR.It was found experimentally that the hydrolysis-condensation products of the system were mainly octasilicate anions when n(TEOS):n(Me₄NOH?5H₂O)=1:0.5?1:1.(2)Under the condition of n(TEOS):n(Me₄NOH?5H₂O)=1:1,octasilicate anions were formed by hydrolysis-condensation and subsequently reacted with different types of chlorosilanes(hydrogen dimethyl chlorosilane,vinyl dimethyl chlorosilane,trimethyl chlorosilane)to produce Q8-type polyhedral oligomeric silsesquioxanes(H-POSS,Vi-POSS,Me-POSS).Subsequently,H-POSS was used as the precursor,grafting allyl methacrylate and methyl methacrylate groups by hydrosilylation reaction to produce liquid viscous MA-POSS and MMA-POSS,respectively.The successful preparation of each POSS was demonstrated by characterization techniques such as Fourier transform infrared spectroscopy(FTIR),matrix-assisted laser-resolved ionization time-of-flight mass spectrometry(MALDI-TOF-MS),nuclear magnetic resonance hydrogen spectroscopy(¹H-NMR),and nuclear magnetic resonance silicon spectroscopy(²⁹Si-NMR).(3)The silicone oils containing vinyl in both chain ends and links were mainly prepared using octamethylcyclotetrasiloxane(D₄)and tetramethyldivinyl disiloxane(MM^vi)catalyzed by alkaline catalysts(alkali gum),and trimethyl-terminated hydrogen-containing silicone oil were vulcanized at high temperature under the catalysis of Karstedt catalyst and the properties of pure silicone rubber were initially investigated.It was found that the pure silicone rubber has the best mechanical properties when the Si-H to Si-Vi ratio is 1.4.(4)Me-POSS and MMA-POSS were introduced into the silicone rubber system by physical compounding,and Vi-POSS and MA-POSS were introduced into the silicone rubber system by chemical grafting.The results showed that the addition of POSS could increase the crosslink density of the composites and improve the thermal stability and mechanical properties.Comparing solid POSS(Me-POSS and Vi-POSS)with liquid POSS(MMA-POSS and MA-POSS),it can be found that liquid POSS can significantly improve the performance of silicone rubber.In addition,it was found that Me-POSS slowly precipitated on the surface of the composite materials when it modified silicone rubber during the experiment.