Silanization Of Silica Catalyzed By Ionic Liquids And Its Influence On Performance Of Rubber Composites

Nowadays,fueled by the increasing consciousness of environment protection and energy saving,green tires with fuel saving,high wear resistance and abrasion resistance have been developed rapidly.As the main reinforcing filler of green tire,silica needs to be modified in situ by silane coupling agents,such as bis?3-triethoxysilylpropyl?-tetrasulfide?TESPT?,to improve the dispersion and the interfacial interaction between silica and rubber matrix.Accordingly,the properties relating to the so-called“magic triangle”of tire?the contradictions among the abrasion resistance,rolling resistance and wet traction of tread?can be improved.However,one major bottleneck for the implementation of TESPT in rubber/silica composites is the low reaction efficiency between silane coupling agents and silica.The silanization reaction between silica and TESPT could be promoted under basic or acidic catalysts.Because of the adjustable acidity and alkality,high thermal stability,high catalytic activity and selectivity in nucleophilic reaction,ionic liquids?ILs?can be used as the catalyst for silanization of silica in rubber matrix.Nevertheless,to date,the systematical investigations on the influence of the structures of ILs or polymers grafted by ILs on the silanization of silica and the structure/performance of the resulted rubber composites are still lacking.Based on the above background,in this dissertation,the author attempts to adopt ILs with different structures to in situ modify the silica/rubber composites,to study the influence of ILs properties on its catalytic activity toward silanization reaction of silica,and to reveal the relationship between ILs properties and the interfacial interactions;Furthermore,the rubber or styrene resin grafted by ILs is used to overcome the aggregation of small molecule ILs,or increase the comprehensive properties relating“magic triangle”.The main contents are as follows.?1?The catalytic activity of ILs for silanization of silica is determined by the alkalinity of anions,which can be adjusted by changing the structure of anions.Then 1-butyl-3-methylimidazole is used as the cation,and PF₆^-,BF₄^-,CH₃COO^-and OH^-are selected as the anions.The alkalinity of the ILs is successively increased.The catalytic activity of ILs for the silanization of silica is improved with the increase of the alkalinity of ILs.The characterization results of model compounds indicate that the silanization of silica catalyzed by ILs with CH3COO^-as anion shows the fastest reaction rate,and the corresponding silanization temperature can be reduced from 245 ^oC to 152 ^oC.In addition,the grafting amount of TESPT also is increased significantly.Further,the ILs was applied to SBR/silica composites.The results show that the comprehensive properties of the composites increase with the degree of silica silanization.?2?The properties of ILs are closely related to the leaving ability of the anion,that is,the binding strength between the anion and the cation.The larger radius of the anion is,the weaker binding strength between the anion and the cation is,that is,the easier the anion leaves.The ILs with triphenylphosphonium as the cation and Cl^-,Br^-,I^-as the anions are synthesized.The leaving ability of the anion in ILs follows the order of Cl^-<Br^-<I^-.The effects of ILs anion leaving ability on the catalytic activity of silica silanization and the properties of SBR/silica rubber composites are revealed.The results show that the stronger the anion leaving ability of ILs is,the higher the catalytic activity of ILs is for the silanization of silica,and the better the comprehensive properties of SBR/silica rubber composites are.With triphenylphosphonium as the cation,and I^-,BF₄^-,PF₆^-as the anion,the effects of anion on the properties of rubber composites are further compared.Although BF₄^-and PF₆^-possess higher leaving ability than I^-,the rubber composites catalyzed by IL containing I^-still show better comprehensive properties as their lower alkalinities are lower than that of I^-.?3?Generally,the ILs exhibit low compatibility with non-polar rubbers and tend to aggregate in the rubbers.Aiming at improving the compatibility between ILs and rubber matrix,1-methylimidazolyl mercaptopropionate ionic liquid?MMP?is grafted onto solution-polymerized styrene-butadiene rubber?SSBR?via thiol-ene click reaction.The MMP moieties on the modified SSBR can still effectively promote the silanization of silica,which improve the dispersion of silica in rubber matrix and enhance the interfacial interaction.Accordingly,at appropriate loading of the graft,mechanical properties and abrasion resistance of the rubber composites are remarkably improved.?4?In the tire industry,C5/C9 petroleum resin is often used to improve the wet traction of the tires.Through Friedel-crafts alkylation,halogen atoms are introduced into the phenyl of styrene resin?SR?,the commonly used petroleum resin.Then the halogen atoms are reacted with triphenylphosphine to yield the phosphonium SR?PSR?.As the main chain structure of PSR has not been changed,it can still effectively improve the wet sliding resistance of rubber composite.At the same time,the ILs moieties on PSR can effectively catalyze the silanization of silica,leading to improved dispersion of silica and enhanced interfacial interaction.Consequently,the reduced rolling resistance and improved abrasion resistance are concurrently achieved.The application of PSR not only improves the wet skid resistance,but also improves the rolling resistance and wear resistance of rubber composite,which provides an effective way to solve the“magic triangle”of the tire treads.