1,4-Bisbenzil: Visible-Light- and Heat-Assisted Crosslinking of Polystyrene Films

Polystyrene (PS) film containing 1,4‐bisbenzil is efficiently crosslinked in two steps. In the first step, visible light (λ > 400 nm) causes molecular oxygen to insert between two carbonyl groups of one of the 1,2‐dicarbonyl groups. The peroxide is subsequently decomposed by absorption of another photon, forming acyloxy radicals, which add to the aromatic ring of the PS chain. The remaining 1,2‐dicarbonyl group is then photoperoxidized to form PS with pendant benzoyl peroxide moieties. In the second step, pendant benzoyl peroxide groups are decomposed thermally to form acyloxy macroradicals responsible for the crosslinking. Crosslinking proceeds simultaneously with degradation. Finally, the gel content in the film may exceed 80 wt%. A novel method of crosslinking of polystyrene films by 1,4‐bisbenzil is presented. The crosslinking occurs in two steps: in the first step, polystyrene film doped with 1,4‐bisbenzil is irradiated with visible light (λ > 400 nm) in the presence of oxygen. In the second step, photoperoxidized polystyrene is subsequently thermal treated to cause crosslinking.