Photopolymerization cyclic ethers

Lewis acids such as BF3 and SbCl5, almost always in conjuction with water or some other protogen, initiate polymerization of cyclic ethers. The initiator and coinitiator form an initiator-coinitiator complex [e.g., BF3 H20, H+(SbCl6) ], which acts as a proton donor (Sec. 5-2a-2). Cationic photopolymerizations are achieved when similar proton donors are formed by the photolysis of diaryliodonium and triarylsulfonium salts (Sec. 5-2a-4). 

More recently, iodonium salts have been widely used as photoinitiators in the polymerization studies of various monomeric precursors, such as copolymerization of butyl vinyl ether and methyl methacrylate by combination of radical and radical promoted cationic mechanisms [22], thermal and photopolymerization of divinyl ethers [23], photopolymerization of vinyl ether networks using an iodonium initiator [24,25], dual photo- and thermally-initiated cationic polymerization of epoxy monomers [26], preparation and properties of elastomers based on a cycloaliphatic diepoxide and poly(tetrahydrofuran) [27], photoinduced crosslinking of divinyl ethers [28], cationic photopolymerization of l,2-epoxy-6-(9-carbazolyl)-4-oxahexane [29], preparation of interpenetrating polymer network hydrogels based on 2-hydroxyethyl methacrylate and N-vinyl-2-pyrrolidone [30], photopolymerization of unsaturated cyclic ethers [31] and many other works. 

The electrophilic behavior of these carbene intermediates is also shown by their reactions with pyridine and with cyclic ethers as electron donors. Pyridine forms betaines of the type 11, which are strongly colored. In 1956, Sirs noted the formation of strongly colored photoproducts with pyridine but assumed these to be C-substituted rather than N-substituted pyridines. Reaction with tetrahydrofuran produces a 1 1 copolymer, which probably arises by the mechanism shown in Scheme 9. The photopolymerization... 

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