Preparation And Characterization Of Siloxane/Titanium Hybrid Polymers With High Refractive Index And Thermal Stability

Silicone materials,which combine the advantages of organic and inorganic materials such as high and low temperature resistance,weather resistance,hydrophobicity,electrical insulation,and biocompatibility,have been widely used in aerospace and aviation,medical treatment,chemical industry,and electronic and electrical equipment.Recently,with the widespread use of light emitting diodes(LED)and their increasing power,there are new demands for packaging materials of LED.Among them,improving the refractive index and thermal stability of packaging materials is an important aspect.In this study,two types of siloxane/titanium hybrid oligomers containing aromatic group in the main chain were successfully synthesized by nonhydrolytic sol-gel reaction,and the obtained oligomers were further reacted by hydrosilylation to form polymers with high thermal stability and refractive index.The effect of titanium element and aromatic group on curing behavior,thermal stability,refractive index,transparency,and thermal aging stability of the polymers was studied.The details are as follows:1.The synthesis and characterization of titanium-silphenylene-siloxane polymersThe titanium-silphenylene-siloxane oligomers(O1,O2,O3,and O4)with different titanium content were synthesized via nonhydrolytic sol-gel condensation from titanium(?)isopropoxide,vinyltrimethoxysilane,and 1,4-phenylenebis(dimethylsilanol)in the presence of barium hydroxide monohydrate as catalyst.Then,the obtained four oligomers were further crosslinked with methylphenyl hydro-silicone oil to form corresponding polymers(P1,P2,P3,and P4)by hydrosilylation reaction.Their structures have been characterized with spectroscopic characterization techniques including FT-IR,1H-NMR,and Raman spectroscopy.Compared with titanium-free polymer P1,the thermal stability,refractive index,and thermal aging stability of titanium-silphenylene-siloxane polymers(P2,P3,and P4)were significantly improved.The titanium-silphenylene-siloxane polymers achieve high refractive indexes(n=1.580-1.584),thermal stability(T5d>500? in nitrogen atmosphere)and optical transparency(?90%at 450 nm).In thermal aging,the polymers exhibited superior performances(?84%at 450 nm after thermal aging at 150? for 120 hours).These data indicate that the polymers have potential application in LED encapsulants.2.The synthesis and characterization of titanium-diphenylether-siloxane polymersThe titanium-diphenylether-siloxane oligomers(O5,O6,O7,and O8)with different titanium content were synthesized via nonhydrolytic sol-gel condensation from titanium(?)isopropoxide,vinyltrimethoxysilane,and 4,4'-bis(dimethylhydroxysilyl)diphenylethe in the presence of barium hydroxide monohydrate as catalyst.Then,the obtained four oligomers were further crosslinked with methylphenyl hydro-silicone oil to form corresponding polymers(P5,P6,P7,and P8)by hydrosilylation reaction.Their structures have been characterized with spectroscopic characterization techniques including FT-IR and 1H-NMR spectroscopy.Compared with titanium-free polymer P5,the thermal stability,refractive index,and thermal aging stability of titanium-diphenylether-siloxane polymers(P6,P7,and P8)were significantly improved.The titanium-diphenylether-siloxane polymers achieve high refractive indexes(n=1.581-1.587),thermal stability(T5d>450 ? in nitrogen atmosphere and T5d>390 ? in air atmosphere)and optical transparency(?90%at 450 nm).In thermal aging,the polymers exhibited superior performances(?87%at 450 nm after thermal aging at 150? for 120 hours).These data indicate that the polymers have potential application in LED encapsulants.