Preparation of 4-Vinylbenzil and Photochemical Properties of Its Homopolymer and Copolymer with Styrene

Abstract

When irradiated at >400 nm in air, pendant benzil groups of 1-phenyl-2-(4-vinylphenyl)-1,2-ethanedione/styrene (VBz/S) copolymer films are transformed almost quantitatively into benzoyl peroxide (BP) groups. Subsequent heating at 91 °C converts the pendant benzoyl peroxide groups to esters and benzoic acid moieties, and there is significantly more cross-linking than main-chain cleavage. Irradiation of the VBz/S copolymer films at 366, 313, and 254 nm also results in formation of BP groups, but they are transformed in situ upon absorption of a second photon by the matrix. The ratios of the relative rate constants for BP formation and subsequent transformation upon absorption by a second photon decrease with decreasing wavelengths of radiation. Irradiation of a film composed of a nonmiscible intimate mixture of poly(1-phenyl-2-(4-vinylphenyl)-1,2-ethanedione) (PVBz) and polystyrene (PS) at >400 nm in air does not lead to discernible BP concentrations as well. Instead, the unreacted pendant benzil groups act as photosensitizers to transform the peroxy moieties almost immediately. In addition, we demonstrate that cross-linking of the VBz/S copolymer film, induced by 254 nm radiation, can be utilized to record a negative image.

Photooxidation of benzil groups in the presence of hindered amine stabilizers in the polystyrene film

“…A homemade "merry-go-round" apparatus was employed in some experiments. 11 The radiation Ͼ400 nm was filtered with glass filter 73087112 (Carl Zeiss, Jena, Germany).…”

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

“…Benzil (BZ) in aerated glassy polymer films can be converted almost quantitatively to benzoyl peroxide (BPO) by insertion of molecular oxygen upon irradiation at λ > 400 nm, that is to say, at the long‐wavelength edge of the n →π* absorption band where BPO does not absorb . By irradiation of copolymer films containing BZ structures, covalently attached BPO pendant groups have also been formed . Whereas a decomposition of low molecular peroxides doped into polystyrene (PS) film results in a decrease in polymer molecular weight, the decomposition of pendant BPO groups in copolymers is an efficient method of crosslinking .…”

“…Such crosslinking of aromatic polymers (e.g., PS) is based on the addition of the pendant polymeric acyloxy radical formed by decomposition of BPO structures to the aromatic ring of another polymer chain. In special cases, the complete crosslinking of copolymers with pendant BZ structures was achieved in only one step by irradiation at a shorter wavelength (366, 313, or 254 nm) . At a shorter wavelength, the light simultaneously decomposes the formed peroxides.…”

“…Applicability of the photochemically generated pendant BPO was investigated for use in both “grafting from” and “grafting to” techniques . Polymers bearing BZ units in the main chain or as pendant groups have been examined as potential negative, or positive resists, where the latter is based on photodegradation of the polymer network. Another application is their use as water‐soluble polymeric photoinitiators .…”

“…Crosslinked PS is usually obtained by irradiation with γ rays with or without added crosslinking agent, post‐modification of PS to form reactive pendant groups, copolymerization of styrene with a monomer bearing reactive group to form a self‐crosslinkable PS, or less commonly by using low molecular crosslinkers such as difunctional Friedel–Crafts reagents or difunctional azides, especially bis(perfluorophenyl azides) …”