Preparation Of Novel Fluorosilicone Rubber Containing Perfluorocyclobutyl Aryl Ether

Fluorosilicone rubber has the excellent performance of fluororubber and organic silicone rubber.In recent years,the demand market of fluorosilicone rubber has expanded rapidly with the development of national economy.The research on fluorosilicone rubber at home and abroad has gradually deepened.There are many deficiencies in the traditional vulcanization system of fluorosilicone rubber and the research of new vulcanization system has become an important direction for the development of fluorosilicone rubber.In this paper,a novel fluorosilicone rubber（Si-PFCB）containing perfluorocyclobutylaryl ether was prepared by cross-linking with[2π+2π]double radical thermal cyclization reaction of aryl trifluoroethylene ether（TFVE）structure.The detail contents and results are as follows:（1）The aryl trifluoroethylene ether monomer was prepared by the fluoroalkylation and dehalogenation reaction,and then the aryl trifluoroethylene ether group was introduced into silane monomer through the Grignard reaction.Finally,the cyclosiloxane with TFVE（M₄）was prepared by hydrolysis reaction under the catalysis of acid.FTIR,NMR and elemental analysis were used to characterize the monomer structure.The thermal analysis by DSC of M₄ shows that the thermal cyclization temperature of the trifluorovinyl aryl ether structure is 160²55^oC,which provides the theoretical foundation for the later vulcanization of fluorosilicone rubber.In addition,it also shows that the monomer is stable under strong acid environment.（2）The polysiloxane containing aryl trifluorovinyl ether（Si-TFVE）was prepared by anionic ring-opening polymerization using M₄ and octamethylcyclotetrasiloxane（D₄）.The effects of the catalysts,such as tetramethylammonium hydroxide（TMAH）,KOH,and the promoters,like DMF,NMP,etc.,on the polymerization were systematically studied and the structure and properties of the new polysiloxane were analyzed.The results show that Si-TFVE（M_n>100,000 g/mol,PDI:1.7².2）with high molecular weight was successfully prepared by using TMAH as catalyst and DMF as promoter,and the polymerization conditions are the reaction temperature of 100^oC,the catalyst dosage of 2.0%,and the molar ratio of catalyst to promoter of 1:160.Si-TFVE prepared with NMP as promoter have a higher molecular weight（M_n>200,000 g/mol,PDI:1.9².2）,and the reaction conditions are the polymerization temperature of 75^oC,the catalyst amount of 2.0%,and the molar ratio of catalyst to promoter of 1:70.The glass transition temperature and melting temperature of Si-TFVE are similar to the ordinary polysiloxane.It is worth noting that the increased randomness of polymers synthesized with NMP as promoter leads to the disappearance of crystallization peaks.When KOH was used as catalyst and DMF as promoter to synthesize Si-TFVE（M_n>100,000,PDI:1.7².0）with high molecular weight and good thermal performance,and the reaction conditions are the polymerization temperature of 80^oC,the catalyst dosage of 2.0%,and the molar ratio of catalyst to promoter of 1:50.The results show that promoter can greatly increase the polymerization reaction rate,reduce the polymerization reaction temperature and shorten the reaction time.Moreover,as the TFVE content increases,the steric hindrance of the polymer segment increases,which makes the molecular weight of Si-TFVE gradually decrease.（3）High temperature vulcanized fluorosilicone rubber was prepared by cycloaddition reaction of TFVE group using Si-TFVE as the base rubber.The basic formula of vulcanized rubber was determined as:100 parts Si-TFVE（0.10%TFVE,mol）,50 parts gas phase silica.The vulcanization process is as follows:the primary vulcanization is 180^oC,0.5 h;the post vulcanization is 190^oC,3 h.Researches show that the mechanical properties,thermal properties（T_g:-120±5^oC）and heat resistance（T₅:450±5^oC）of vulcanized rubber are comparable to ordinary high-temperature vulcanized silicone rubber.The mechanical strength of the vulcanized rubber was lower when TMAH was used as catalyst and DMF as promoter,while the tensile strength of the vulcanized rubber is 6.9 MPa,the tearing strength is 35.34 kN/m and the elongation at break is 1685%when NMP was used as promoter.The tensile strength of the vulcanizate with KOH as catalyst and DMF as promoter is 6.3 MPa,the tear strength is 33.5 KN/m,and the elongation at break is 1152%.