N‐alkoxypyridinium salts as coinitiators in radical polymerization: Synthesis and Photochemical Properties

Abstract

A few N-alkoxypyridinium salts are developed as photoinitiators for efficient polymerization reactions. They are characterized by absorption properties below 300 nm, and generate alkoxy radicals on UV-Vis light exposure. The squarylium dye was used as a blue-light photosensitizer. Polymerization results are correlated with the photochemistry of N-alkoxypyridinium salts. The quenching of the excited singlet state of squarylium dye by pyridinium salt and the formation of the semioxidized species of squaraine suggests an electron transfer from an excited dye to a coinitiator, and that the resulting oxygen-centered radical initiates the polymerization process.The chemical mechanism was investigated by steady state photolysis and nanosecond laser flash photolysis experiments. Photoinitiating activity of new photoinitiators for initiation of polymerization of trimethylolpropane triacrylate in the UV-blue light region was compared with photoinitiating ability of selected commercially available initiators.

Recent progress in the development of highly active dyeing photoinitiators based on 1,3-bis(p-substituted phenylamino)squaraines for radical polymerization of acrylates

“…Two squarylium dyes, 1,3-bis(phenylamino)squaraine (SQ1) and 1,3-bis( p -bromophenylamino)squaraine (SQ2), were selected and used as visible light absorbers and combined with different radical sources. 107–110…”

“…In this study, bimolecular PISs based on 1,3-bis( p -bromophenylamino)squaraine (SQ2) and new onium salts (NO–NO5), the chemical structures of which can be found in Table 2, were studied. 109 Indeed, this series of six various N -alkoxypyridinium salts is an effective source of radicals. As is shown in Fig.…”

“…The highly efficient two-component photoinitiating systems composed of p -substituted bromide derivative as SQ2 dye and different radical sources, such as N -alkoxypyridinium salts NO and NO4, were compared with a system comprised of a popular photoinitiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) and the combination of camphorquinone/ N -methyldiethanolamine (CQ/MDEA) or camphorquinone/ N -phenylglycine (CQ/NPG). 109 The structures of these compounds are presented in Table 2. As shown in Fig.…”

Recent advances on squaraine-based photoinitiators of polymerization

“…In line of the previous study, influence of the substitution pattern of a series of Nalkoxypyridinium salts used as co-initiators was carried out, still while using SQ2 as the photosensitizer (See Figure 13). [206] Figure 13. Chemical structures of N-alkoxypyridinium salts NO1-NO5 used as co-initiators with SQ2.…”

Photochemical generation of electron poor reactive intermediates: Photochemistry of S-alkoxy dibenzothiphenium tetrafluoroborates, N-alkoxy pyridinium perchlorates, and Sulfonium ylides

“…A precedent for this pathway has not been seen in our previous investigation of the organosulfur compounds, but it is widely believed that photolysis of N-alkoxy derivatives of pyridine, quinoline, isoquinoline, and phenanthridine are photochemically cleaved in the homolytic mode, generating alkoxy radicals and nitrogen-based radical cations. [28][29][30][31][32][33] A quantum yield of 0.48 for N-ethoxy quinolinium photohomolysis has been reported. 28 These compounds also rapidly and…”