| Viscoelastic materials are widely used as damping materials because of their unique damping properties.Silicone rubber belongs to viscoelastic materials,which has excellent resistance to high and low temperature,and has excellent mechanical properties from-50 to 200℃, the damping capacity is stable with a wide range of temperature and frequencies,comparing with other high molecular materials.But the damping value is low in general case,so we need to improve the damping capacity.There are three method commonly used:(1)change the main chain of silicone rubber by copolymerization(2)mix different kinds of polymer(3)add the damping addictive to polymer matrix.In this paper,we prepare the raw silicone rubber by random copolymerization and the damping addictive,then combine the two substances.Thus prepared silicone rubber has the advantage of both wide temperature range and high damping.Ethyl silicone rubber has the lowest glass transition temperature(-138℃)among all silicone rubber, and has an excellent resistance to low temperature.Compared with methyl silicone rubber, the volume of its side chain is larger,thus it has better damping performance. The introduction of phenyl group increases the volume of side chain furthermore and improves the intermolecular rotational resistance,which improves the damping ability of ethyl silicone rubber.Besides, the modulus of ethyl silicone rubber is constant with the changes of temperature, so the silicone rubber containing methylphenylsiloxane units and diethylsiloxane units has characters of high damping and constant modulus.We prepare high molecular diethylsiloxane-co-methylphenylsiloxane(Et2SiO-MePhSiO)and dimethylsiloxane-c o-diethylsiloxane-co-methylphenylsiloxane (Me2SiO-Et2SiO-MePhSiO) by using the hexaethyl cyclotrisiloxane(D3Et),cyclic mixture of methyl phenyl cyclosilo xanes(Dnph,n=3,4,5), octamethylcyclotetrasiloxane(D4),tetramethyl tetravinyl cyclotetra siloxane(D4Ⅵ) as raw material and KOH as catalyst,and we characterized the unvulcanized and vulcanized rubber.The results showed that the damping capability increases firstly and then decrease with the phenyl contents increasing,and the damping value reaches the best when the phenyl contents is 40%.The modulus of silicone rubber containing diethylsiloxane units varies little with temperature.Damping addictives containing side chain of phthalimide and 1,8-naphthalene are synthesized by reaction between the active propyl group of ammonia propyl phenyl silicone oil and aromatic acid anhydride.The damping addictive not only has bulky polar group,but also has n-n plane structure. The bulky polar group can improve the intermolecular internal friction, and π-π interaction between polymer matrix and damping addictive enhances the damping property.By choosing 30%methyl phenyl silicone rubber as polymer matrix,we study the effect of molecular,imide side chain,and vinyl content on the damping performance of material.Experimental results show that silicone rubber and damping addictive are incompatible,glass transition temperatures of the two substances are quite different,and the temperature corresponding to tanδmax is about 0℃.By changing factors——adding amounts, crosslinking density and molecular weight—we determine that the optimum formula of damping addictive is,vinyl content(1%), the molecular weight (50,000),adding quantity(20parts).The glass transition temperature shifts to high temperature with the increasing of aminopropyl contents of silicone oil.In order to broaden the damping temperature range of silicone rubber matrix,several kinds of methyl phenyl silicone rubber(phenyl contents 20%,30%,40%,60%) are blended,and we study the effect of damping addictive on damping property of blending material.Results show that when the mass ratio of 40% methyl phenyl silicone rubber:60%methyl phenyl silicone rubber=2:l,the effect is the best. We can change the 40%methyl phenyl silicone to 40% ethyl phenyl silicone rubber to further improve the damping cability and temperature range (-50—-room temperature). |
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