Trialkyl Phosphites and Diaryliodonium Salts as Co-initiators in a System for Radical-Promoted Visible-Light-Induced Cationic Polymerization

Abstract

Trialkyl phosphites ((RO)3P) can act as co-initiators for the diaryliodonium-induced cationic polymerization of cyclohexene oxide (CHO) or THF. A radical initiation step is also required, consistent with the essential role of a radical chain reaction of the phosphite with the iodonium salt to form polymerization-starting aryltrialkoxyphosphonium salts (ArP(+)(OR)3). We used the visible photolysis of phenylazoisobutyronitrile (PAIBN) as the radical initiation step. The presence of multiple fluorine substituents on the phosphite, as in tris(2,2,2-trifluoroethyl) phosphite (TFP), allows polymerization to proceed with a minimal amount of chain transfer from nucleophilic attack by the phosphite. In a typical experiment, a CHO solution of bis(4-tert-butylphenyl)iodonium hexafluorophosphate (0.05 M), TFP (0.1 M), and PAIBN (0.02 M) was illuminated with a 65-W compact fluorescent bulb for 1 h, resulting in a 78% conversion to poly(cyclohexene oxide) with an average molecular weight (MW) of 25000. We also used competition experiments to determine approximate rate constants for reactions of phenyl radicals with CHO (k = 2 × 10(6) M(-1) s(-1)) and with TFP (k = 2 × 10(8) M(-1) s(-1)).

Photoinduced Electron Transfer Reactions for Macromolecular Syntheses

“…Later studies revealed that modification of phosphites with halogen-substituted alkoxy groups reducing their nucleophilicity could suppress any inhibitory activity of phosphite compounds to allow an efficient polymerization process (Scheme 15). 216 Promotion of cationic polymerization by free radicals produced by Type II photoinitiators has been investigated. As Type II photoinitiators thioxanthone, benzophenone, and camphorquinone and related structures have been employed in this connection.…”

Solvent‐free ring‐opening polymerization of cyclohexene oxide catalyzed by palladium chloride

“…The thermal latent catalysis polymerization of CHO is widely used in industry, but it often has a poor polymerization yield, and the catalysts usually require tedious multistep process to synthesize. Considerable efforts have been devoted to finding new catalysts with improved CHO polymerization yield . Onium compounds (eg, iodonium, pyridinium, and sulfonium salts) and metal complexes have been reported to show catalytic activity when aided by light and/or a cocatalyst.…”

“…Considerable efforts have been devoted to finding new catalysts with improved CHO polymerization yield. [9][10][11][12][13][14][15][16][17][18][19] Onium compounds [9][10][11][12][13][14][15] (eg, iodonium, pyridinium, and sulfonium salts) and metal complexes 16,17 have been reported to show catalytic activity when aided by light and/or a cocatalyst.…”