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Improving Thermal and Chemical Stabilities of Electronic Epoxies using Polysiloxane Copolymers Part II: Block Copolymers

In this paper the improvements of the thermal stability of cured epoxy resins in air as well as in various critical media like water, solvents, aerospace and automotive fluids were investigated. Being modified with different addition levels of polysiloxane-epoxy block copolymers, the toughness was increased significantly without sacrificing the transparency of the cured resins. The embrittlement upon thermo-oxidative ageing of the epoxy resin could be reduced significantly. Losses in strength and elongation caused by thermo-oxidative degradation of the polymer were minimized. The hygrothermal stability was increased significantly as well. It was found that the coefficient of thermal expansion (CTE) at temperatures above the glass transition temperature increased tremendously upon heat ageing of the unmodified control, but not for a modified resin system. This enables the epoxy resin formulator to create systems for various electronic applications with a much better dimensional stability and an increased service life under harsh conditions.