Synthesis and photooxidation of styrene copolymer bearing camphorquinone pendant groups

Branislav Husár,Norbert Moszner,Ivan Lukáč

doi:10.3762/bjoc.8.37

Branislav Husár, Norbert Moszner + Show 1 more

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https://doi.org/10.3762/bjoc.8.37

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Abstract

(±)-10-Methacryloyloxycamphorquinone (MCQ) was synthesized from (±)-10-camphorsulfonic acid either by a known seven-step synthetic route or by a novel, shorter five-step synthetic route. MCQ was copolymerized with styrene (S) and the photochemical behavior of the copolymer MCQ/S was compared with that of a formerly studied copolymer of styrene with monomers containing the benzil (BZ) moiety (another 1,2-dicarbonyl). Irradiation (λ > 380 nm) of aerated films of styrene copolymers with monomers containing the BZ moiety leads to the insertion of two oxygen atoms between the carbonyl groups of BZ and to the formation of benzoyl peroxide (BP) as pendant groups on the polymer backbone. An equivalent irradiation of MCQ/S led mainly to the insertion of only one oxygen atom between the carbonyl groups of camphorquinone (CQ) and to the formation of camphoric anhydride (11) covalently bound to the polymer backbone. While the decomposition of pendant BP groups formed in irradiated films of styrene copolymers with pendant BZ groups leads to crosslinking, only small molecular-weight changes in irradiated MCQ/S were observed.

Highlights

Camphorquinone (CQ) in the presence of H-atom donors such as ethers (H abstraction), or more efficiently tertiary amines, is known to be an effective photoinitiator for curing methacrylate-based dental restorative resins [1,2,3,4,5,6,7,8,9]
Racemic MCQ was synthesized in seven steps from (±)-10camphorsulfonic acid (1) as a starting material in 18% overall yield (Scheme 2, see Supporting Information File 1 and Supporting Information File 2 for full experimental data)
Without the need for an enantiopure product, the reaction economics could be improved both by the use of a cheaper racemic starting material and by a simplified multistep synthesis

Summary

Introduction

Camphorquinone (CQ) in the presence of H-atom donors such as ethers (H abstraction), or more efficiently tertiary amines (electron/proton transfer), is known to be an effective photoinitiator for curing methacrylate-based dental restorative resins [1,2,3,4,5,6,7,8,9]. Triplet state of the carbonyl group of CQ abstracts an H-atom from a hydrogen donor. The rate-determining step in photoinitiation by CQ/amine is hydrogen transfer by the excited n→π* triplet state of the carbonyl group of CQ from the alkylamino group [8,9]. The photochemistry of the low molecular CQ in the polystyrene (PS) film

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