Addition-fragmentation type initiation of cationic polymerization using allyloxy-pyridinium salts

Abstract

Allyloxy-pyridinium salts with various substituents on the allylic moiety are shown to be very efficient coinitiators in radical promoted cationic polymerization of cyclohexene oxide. Depending upon the radical initiator chosen, cationic polymerizations may be initiated by either heat or light. For the most part, the mechanism of initiation involves the addition of free radicals formed by the radical initiator, and a subsequent fragmentation of the energy-rich intermediate yielding initiating pyridinium type radical cations. In additionÈ fragmentation polymerization, the substituent at the allylic moiety does not sig-niÐcantly inÑuence the polymerization rate, thus implying that fragmentation is the rate determining step. In some cases, oxidation of the primarily formed free radicals contributes to the formation of initiating species. The salts under investigation are also able, to various extents, to initiate cationic polymerization upon external stimulation (heating or UV irradiation) without added radical initiators.Society of Chemical Industry ( 1998

The Effect of the Heteroatom Moiety of Allylic Salts on the Addition Fragmentation Initiation of Cationic Polymerization

“…tution at the allylic double bond. [15] Since addition reactions are very much affected by the substituents at the double bond, it is clear that the addition reaction in our case is not rate determining.…”

Cationic photopolymerization with the aid of pyridinium-type salts

“…Apart from the sulfonium salt dealt with in that section, allyloxy pyridinium salts 5 + X -, 6 + X -, 7 + X -, and 8 + X -, as well as allyl pyridinium salt 9 + X -(Tab. 2) were studied [32][33][34][35] . These salts exhibit a behavior similar to that of 1 + PF 6 -, e. g., they initiate cationic polymerization of CHO upon irradiation at wavelenghts at which they are light-absorbing, i. e. at k inc a 300 nm.…”

“…shows how CHO containing allyloxy pyridinium salt but no free radical source is polymerized upon irradiation at k inc = 280 nm where the salts absorb light 32) . The conversion-time profiles are S-shaped because impurities must be consumed prior to the onset of chain growth (this causes the induction period) and because of the total consumption of the onium salt (this causes the saturation).…”

“…However, polymerization was induced upon addition of a free radical source as can be seen from Fig. 11 32) . Here, benzoin (2.4 6 10 -2 mol N L -1 ) was used.…”

A Novel Bifunctional Addition-Fragmentation Agent for Photoinitiated Cationic Polymerization

“…[3] Among these, recently developed allyl-onium salts, [4][5][6][7][8][9][10][11][12][13] which initiate via addition-fragmentation mechanism, are a promising novelty (see Scheme 2).…”