UV-A mediated transformation of liquid polybutadiene into robust thermosets via a dual-action photo-reagent

This study demonstrates an efficient approach for the photovulcanization of liquid polybutadiene (pBD) under UV-A irradiation by using phenacyl bromide (PhABr) as a dual-action photoinitiator. Spectroscopic analysis such as FTIR and NMR revealed a radical-mediated relatively rapid crosslinking initiated by the homolytic cleavage of PhABr. The solid-state UV–Vis spectroscopy demonstrated high optical transmittance throughout the visible region. Thermal characterization via DSC showed a drastic increment of the glass transition temperature (Tg) from a theoretical baseline (−98 ℃) to −20 ℃, with the 10 wt% loading. Mechanical testing confirmed the changes by showing a linear increase in Young’s modulus and tensile strength as the material transforms from a viscous liquid into a rigid thermoset. Gel fraction experiments confirmed the formation of a robust 3D network (Gf > 87%). Furthermore, surface analysis (SEM and WCA) provided evidence that the photovulcanization is spatially uniform, producing smooth, defect-free films. A significant drop in the water contact angle from 99° to 86° at higher loadings revealed the increment in surface polarity due to photooxidation.