Preparation And Properties Of Methylethylvinylsilicone Rubber

The main factors that affect the low temperature resistance of silicone rubber are glass transition temperature and crystallization behavior.PDES has a low glass transition temperature while it is easy to crystallize at low temperatures,which effects the use in extremely cold environments.Currently,the primary means of reducing the crystallinity of PDES is destroying the macromolecule chain regularity via the method of copolymerization.However,copolymerization has some shortage,such as harsh reaction conditions and longer reaction times.This paper provides a more convenient way to prepare a kind of low temperature resistant silicone rubber.This paper mainly contains two aspects:the first is the synthesis and structure characterization of poly(methylethylvinylsiloxane)with high molecular weight.The other is the preparation of high temperature vulcanized methylethylvinylsilicone rubber and characterization of their cured performances.The high molecular weight of poly(methylethylvinylsiloxane)is successfully synthesized by using 2,4,6,8-tetraethyl-2,4,6,8-tetramethylcyclotetrasiloxane(D4Me.Et)as the main monomers via anionic ring-opening polymerization.In this process,by comparing the catalytic system of M1,M2 and M3,we find that M3 can be used to synthesize poly(methylethylvinylsiloxane)with high molecular weight.That's because catalytic reaction temperature of M3 is higher and its' activity is high.The structure of poly(methylethylvinylsiloxane)were characterized by Fourier transform infrared spectroscopy(FTIR),nuclear magnetic resonance(NMR)and differential scanning calorimetry(DSC).Infrared spectroscopy(FTIR)and 1HNMR results indicated the existence of methyl(-CH3),ethyl(-CH2CH3)and vinyl(-CH=CH2)groups in the poly(methylethylvinylsiloxane).29Si NMR spectrum displayed that there exist signal peak of methylethylsilicone chain(MeEtSiO)at-22.4ppm,meanwhile the signal peak of methylvinylsiloxane chain(MeViSiO)is not significantly present because of its low content in the polysiloxane.The DSC results show that the poly(methylethylvinylsiloxane)were non-crystallization polymer with low glass transition temperature.The peroxide cured high temperature vulcanized methylethylvinylsilicone rubber was prepared by using organic peroxide(V-A,V-B,V-C,V-D)as curing agent.The effects of the silica amount,the content of vinyl group and the amount of curing agent on the mechanical properties of vulcanized rubber were studied.The optimum formulas was obtained in view of the mechanical properties and curing curves of methylethylvinylsilicone rubber with 50phr TS-530,0.6phr curing agent and gum containing 0.15mol%vinyl groups.Moreover,the vulcanization curves showed that in curing system of V-A,only vinyl group participated the crosslinking reaction,while the V-B can vulcanize the vinyl,but also allow some ethyl groups participate cross-linking reaction.The hydrosilylation cured high temperature vulcanized silicone rubber was prepared by using PHMS as the crosslinking agent.The mechanical properties and crosslinking density of silicone rubber were investigated by using PHMS with hydrogen content of 0.5wt%(PHMS-0.5)and PHMS with hydrogen content of 1.0wt%(PHMS-1.0)as the crosslinking agent respectively.The results showed that in the cross-linking system of PHMS-0.5,when the molar ratio of SiVi and SiH is 1:7,the mechanical properties of the silicone rubber are the best and the crosslinking density is the largest.In the cross-linking system of PHMS-1.0,when the molar ratio of SiVi and SiH is 1:11,the mechanical properties of the silicone rubber are the best and the crosslinking density is the largest.