Synthesis and properties of transparent cycloaliphatic epoxy–silicone resins for opto-electronic devices packaging

Cycloaliphatic epoxy–silicone resins were successfully synthesized through a two-step reaction route: (і) hydrosilylation of 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) and 1,2-epoxy-4-vinyl-cyclohexane (VCMX), (іі) blocking of unreacted SiH in (і) with n-butanol. The molecular structures of the cycloaliphatic epoxy–silicone resins were characterized by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (1H NMR and 29Si NMR). High grafting efficiencies of epoxy groups were confirmed by 1H NMR combined with weighting results, indicating over 90 mol% of cycloaliphatic epoxy were grafted on the silicone resins. Subsequently, SiH groups from TMCTS were almost totally consumed after the blocking reactions. In comparison with commercial available cycloaliphatic epoxy resin 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ERL-4221) cured by MHHPA, the cured cycloaliphatic epoxy–silicone resins exhibited better thermal stability, lower water absorption and higher UV/thermal resistance. Moreover, the characteristics of transmittance (>90%, 800 nm), 5 wt.% mass loss temperature (>330 °C) and no yellowing during thermal aging at 120 °C or UV aging for 288 h of the cured cycloaliphatic epoxy–silicone resins, made them possible for power light-emitting diode (LED) encapsulants, or other packaging materials, like optical lenses, and electronic sealings.

► Cycloaliphatic epoxy–silicone resins were prepared by a two-step reaction.
► The synthesized resins exhibited good compatibility and high transparent.
► Properties of cured resins with different epoxy values were studied.
► Excellent UV resistance and thermal stability of the cured resins.
► Potential application of the cured resins in LED packaging.