| The advancement of science and technology has broadened the scope and scenes of human activities.Some specific occasions like automobile brake devices in severe cold areas,need rubber products to work in low temperature and oily environments for long time.Especially in recent years,the fields of aerospace and polar exploration have developed rapidly,which puts forward higher requirements to the extreme environmental resistance of rubber products.Among all the rubber varieties,silicone rubber has become a very popular choice due to its excellent high and low temperature resistance and radiation resistance.Among them,the most widely used silicone rubber variety is methyl vinyl silicone rubber(MVQ).MVQ has excellent vulcanization properties and low glass transition temperature,however,due to its regular molecular chain,the rubber will undergo a strong crystallization reaction at-50? and lose elasticity accordingly.In addition,MVQ has insufficient resistance to non-polar oils,and low-polar side groups are an important reason for this phenomenon.In order to solve these problems,it is an excellent choice to destroy its regular structure and increase its polarity by introducing polar groups.In this paper,epoxy groups and-OH,-COOH and-COOCH3 groups were introduced into MVQ molecular chain through epoxidation and thiol-ene click reaction,respectively,the low-temperature crystallization and resistance to non-polarity solovent performance of the modified silicone rubber were improved dramatically,and practical application with great significance may be developed in the future.The main contents are as follows:(1)MVQ with 10%-50%vinyl content were synthesized using anionic ring-opening polymerization method by controlling the ratio of octamethylc-yclotetrasiloxane(D4)and tetramethyltetravinylcyclotetrasiloxane(V4)(commercial MVQ vinyl content is usually below 1%),the molecular weight was about 35,0000.Then the resulted MVQ was epoxidized with m-chloroperoxybenzoic acid(MCPBA),and methyl vinyl silicone rubber(EMVQ)with an epoxy degree of over 90%was obtained.A pilot test with a maximum capacity of 50-200L was carried out,After epoxy modification,the low-temperature crystallization phenomenon was suppressed,and the glass transition temperature(Tg)was slightly increased.The oil resistance performance was slightly improved when the grafting amount is above 40%.In the pilot test,it was found that as the reaction capacity increases,the probability of chain scission side reactions would increase.(2)The in situ epoxidation of MVQ was innovatively explored with large doses of hydrogen peroxide and formic acid,and the epoxide group was successfully introduced into the MVQ molecular chain.At present,the highest epoxide degree could reach 15.4%,and serious ring-opening side reactions would occur in the later stage of the reaction.(3)Using different thiol reagents and click chemistry,-OH,-COOH and-COOCH3 groups were introduced into the MVQ molecular chain,It was found that-COOCH3 has good stability to the click reaction.While MVQ grafting-OH and-COOH caused a strong cross-linking reaction when the vinyl content was above 10%.The reaction of MVQ grafting-COOCH3 with 10%-50%vinyl content was studied in detail.The effects of the concentration,the amount of initiator,and the molar ratio of sulfhydryl group to double bond on the click reaction were studied.The optimized reaction conditions were as follows:the amount of initiator was 1%mol of double bond,the molar ratio of sulfhydryl group to double bond was kept below 3:1,and the concentration of the glue was determined by the different content of vinyl.The introduction of polar groups effectively inhibited the low-temperature crystallization of MVQ,and its cold-resistant compressibility at-70? could reach up to 0.7.After modification,The surface contact angle of MVQ could be reduced from about 108° to 50°,and its resistance to IRM908 oil increased by about 80%. |
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