Modification of Epoxy Resin with Cycloaliphatic-Epoxy Oligosiloxane for Light-Emitting Diode (LED) Encapsulation Application

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A novel cycloaliphatic-epoxy oligosiloxane (EHDM) was incorporated into 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ERL-4221) for use as a light-emitting diode (LED) encapsulant. EHDM, with reactable epoxy groups and flexible Si-O-Si chains, was obtained by the hydrolytic condensation reaction between 2-(3,4-epoxycyclo-hexyl)ethyl-trimethoxysilane (EHETMS) and dimethyldiethoxylsilane (DMDES). The results of Fourier transform infrared spectroscopy, 29Si nuclear magnetic resonance, and gel permeation chromatography indicated that EHDM had a narrow molecular weight distribution and high epoxy graft degree. The thermal and mechanical properties, morphologies, and light transmittance of the cured neat epoxy resin and EHDM-modified epoxy were investigated by differential scanning calorimetry, thermogravimetric analysis, tensile and impact testing, scanning electron microscopy, and ultraviolet-visible spectrophotometry. The experimental results demonstrated that the cured EHDM-10 hybrimer with 10 pph of EHDM relative to ERL-4221 maintained the neat ERL-4221 epoxy transmittance of 85% at 450 nm. With respect to the corresponding properties of the neat epoxy resin, EHDM-10 hybrimer possessed a higher glass transition temperature, better thermal stability, better fracture toughness, and lower water absorption ratio, indicating EHDM effectively improved the properties of ERL-4221 for LED packaging applications.