A system consisting of a novel N-allyloxypyridinium salt and a radical initiator is highly appropriate for the thermal initiation of cationic polymerizations. Radicals formed upon the thermolysis (at 70 "C) of initiators as 2,2'-azoisobutyronitrile or benzoyl peroxide add to the double bond of the pyridinium salt N-[2-(ethoxcarbonyl)allyloxy]-~-picolinium hexafluoroantimonate (1). Subsequently, the pyridinium salt is fragmented yielding pyridinium-type radical cations, species able to initiate cationic polymerizations. In the case of the radical initiator phenylazotriphenylmethane (triphenylmethaneazobenzene), the polymerization is extremely rapid, since additionally the triphenylmethyl cation formed by electron transfer initiates the polymerization. The initiation capability of the system described was demonstrated for a number of monomers, such as cyclohexene oxide, butyl vinyl ether and the bifunctional 3,4-epoxycyclohexylmethyl 3',4'-cyclohexanecarboxylate. With the latter, an insoluble polymer network was readily obtained.
A novel allyloxy‐picolinium salt, N‐[2‐(methyl)allyloxy]‐α‐picolinium hexafluoroantimonate, has been synthesized and used as addition–fragmentation agent for radical promoted thermal and photochemical cationic polymerization of monomers such as cyclohexene oxide, p‐methoxystyrene and various vinyl ethers. Polymerization by heat was achieved using the allylic salt in conjunction with benzoyl peroxide (BPO), phenylazotriphenylmethane (PAT) and 2‐2′‐azobis‐isobutyronitrile (AIBN). Polymerization rates were found to drop in the order PAT>BPO>AIBN. Photopolymerization was carried out by irradiating the allyloxy‐picolinium salt in the presence of monomer at 280nm. Upon adding benzoin as free radical source, the spectral response was extended to 370nm. The initiation mechanism is explained in terms of an addition–fragmentation scheme. © 1997 SCI.
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
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