One‐step, one‐pot photoinitiation of free radical and free radical promoted cationic polymerizations

Abstract

ABSTRACT:We describe here a novel approach to photoinitiate free radical and cationic polymerizations concurrently, involving the use of benzoin in conjunction with an onium salt such as diphenyl iodonium or N-alkoxy pyridinium salt. On photolysis, benzoyl radicals formed from the decomposition of benzoin initiate free radical polymerization of methyl methacrylate. The hydroxy benzyl radicals formed concomitantly are readily oxidized to the corresponding cation by the onium salt to initiate cationic polymerization of cyclohexene oxide in the same system. Evidence for two independent polymerizations was obtained from studies involving gel permeation chromatography, extractions, and infrared and proton nuclear magnetic resonance analysis of the polymers. The effect of the type of the onium salt on each polymerization was also investigated.

Diethoxy‐azobis(pyridinium) Salt as Photoinitiator for Cationic Polymerization: Towards Wavelength Tunability by Cis–Trans Isomerization

“…Upon photolysis, these salts undergo cleavage of the nitrogen-oxygen bond to form radical cations and alkoxy radicals and initiate the respective polymerizations independently [22,26] or concurrently. [27] Like other cationic photoinitiators, N-alkoxy pyridinium salts exhibit poor spectroscopic response at high wavelengths. A number of pathways that involve electron N,N 0 -diethoxy-4,4 0 -azobis(pyridinium) hexafluorophosphate (DEAP) has been synthesized by alkylation of the corresponding N-oxide and characterized.…”

Redox Initiated Cationic Polymerization: Reduction of Triarylsulfonium Salts by Silanes

“…Similarly, oxidizable free radicals generated either by thermolytic or by photolytic methods can be used as reducing agents for diaryliodonium salts. A number of research groups including those of Ledwith [12], Timpe and Baumann [13][14][15][16][17], Yagci [18][19][20][21][22] and Fouassier [23][24][25] have explored this latter route for carrying out the cationic polymerizations of a variety of classes of monomers. All attempts thus far to extend these same methods to the corresponding reduction of triarylsulfonium salts have met with very limited success.…”

Novel visible photoinitiators systems for free-radical/cationic hybrid photopolymerization

“…A variety of radical initiators have been used including 2,2-dimethoxy-2-phenylacetophenone [2,9,14,16], 1,2-diphenylethanedione [9], hydroxyphenyl-ketone [7,10,11], bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide [12], and benzoin [2], whereas sulfonium [2,9,16], iodonium [2,7,10,11,12,16] and pyridinium [2] salts have been employed as cationic initiators. UV curing was then performed on these hybrid initiator systems that contained bifunctional crosslinkable monomers glycidyl meth/ acrylate [9], methacrylateesiliconeeepoxycyclohexanepoxide [13], 3,4-epoxycyclohexylmethyl methacrylate [14], 3-(1-propenyloxypropyl) acrylate [17] or mixtures of certain acrylates and either epoxides [2,7,10], vinyl ethers [1,6,12], or oxetanes [2,16].…”

“…The properties of the two constituent homopolymers often combine synergistically in the hybrid polymer. For example, the combination of free radical and cationic polymerization methods has led to the preparation of unusual hybrid polymer structures such as multiblock [1,2], graft [3,4] and random [5,6] copolymers and interpenetrating polymer networks (IPNs) [7,8].…”