Facile fabrication of eugenol-containing polysiloxane films with good optical properties and excellent thermal stability via Si–H chemistry

Abstract

Transparent and easily fabricated films were obtained through the coupling of eugenol, a bio-sourced feedstock, and poly(methylhydrosiloxane), via the Piers–Rubinsztajn reaction and Pt-catalysed hydrosilylation. The precursor reagents are readily available and economical, and the reaction process used was mild and easily undertaken. Additionally, poly(methylhydrosiloxane), having an abundant source of pendant Si–H groups, can be cross-linked with eugenol at multiple juncture points, and thus the eugenol content in these films ranges from 13.12 to 45.42 wt%. It was found that as the eugenol content increased, the thermal stability of the films also improved, with T_10% and R_w at 700 °C ranging from 350.1 to 584.3 °C and 46.41 to 86.63%, respectively, which is higher than other analogous biomass-derived polysiloxanes. Crucially, the prepared films also exhibited suitable optical properties, with a >90% transmittance within the 430–1100 nm region and near 100% absorbance in the UV region (<350 nm), verifying their potential applications as optical encapsulants. Aside from good light transmittance, the refractive index of the films increased from 1.44 to 1.52 (at 450 nm) with higher ratios of eugenol. This demonstrates their suitability for use as high-refractive index (>1.5) LED encapsulants and also in stacked multi-layer reflectors. In addition, to protect the encapsulated chips from moisture erosion, these films exhibit good water vapour barrier properties and water repellence.