Difunctional epoxy siloxane monomers containing disiloxane, trisiloxane, and tetrasiloxane were prepared by hydrosilylation of an ␣,-difunctional SiOH-terminated siloxane with a vinyl-functional epoxide. Cationic polymerization of these monomers using 3-methyl-2-butenyltetramethylenesulfonium hexafluoroantimonate and their reactivities were examined. The reactivity order was disiloxane Ͼ trisiloxane Ͼ tetrasiloxane. Thermal discoloration of these polymers increased with catalyst concentration and also with the length of dimethyl siloxane. UV discoloration was also accelerated by catalyst. From the thermo gravimetric analysis, it was found that the thermal stabilities of polymers increased with increasing the length of dimethyl siloxane chain. Mechanical properties of polymers were also tested by thermal mechanical analysis and dynamic mechanical analysis, and it was found that the flexibility of polymers was increased with increasing siloxane chain length.

A novel epoxy siloxane hybrid was prepared using epoxy siloxane monomers of 1,3-bis[2-(3-{7-oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane (BEPDS) with hydroxyl terminated hydrogenated polybutadiene (GI-1000), in different proportions. Apparent polymerization reactivity was decreased with increasing GI-1000 concentration but the normalized reactivity per epoxy group was slightly increased due to reaction between hydroxyl group and epoxy group. Increasing GI-1000 concentration showed significant flexibility improvement in epoxy siloxane hybrid. At 30 wt % of GI-1000 addition, glass transition temperature was decreased from 116 to 218C and shore D hardness was decreased from 75 to 46.5% weight loss temperature of these epoxy siloxane hybrid was decreased with increasing GI-1000 concentration, whereas thermal discoloration was increased. LED encapsulation with this epoxy siloxane demonstrated no crack when GI-1000 was 30 wt % or more.

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