Visible light photopolymerization employing 2,4‐diiodo‐6‐butoxy‐3‐fluorone and tetraorganylborate salts as photoinitiators

Abstract

SYNOPSISSeveral new tetraorganylborate salts have been synthesized and tested as coinitiators with 2,4-diiodo-6-butoxy-3-fluorone (DIBF) for the photopolymerization of acrylic monomer mixtures. The rate of photopolymerization has been found to be a function of chemical structure of the borates. Stability, solubility, and reactivity of these borates as coinitiators for photopolymerization have been investigated. Diphenyldialkylborates have been found to be the best among the tested coinitiators. 0 1996 John Wiley & Sons, Inc.

The influence of a radical structure on the kinetics of photopolymerization

“…Tetraorganylborate salts may be oxidized by several photoexcited oxidizing agents to release free radicals that may be used to initiate chain polymerization . There are many examples of two‐component photoinitiating systems working through electron transfer process composed of organic borate salts.…”

“…There are many examples of two‐component photoinitiating systems working through electron transfer process composed of organic borate salts. Polymethine dyes, 2,4‐diiodo‐6‐butoxy‐3‐fluorone, 5,7‐diiodo‐3‐butoxy‐6‐fluorone, xanthenes, fluorones, benzophenone were used as photosensitizers in such photoinitiating systems . The generation of initiating radicals is a result of decomposition of unstable boranyl radical formed after electron transfer process from borate anion to an excited singlet state of photosensitizer (Scheme ) …”

Synthesis of tetramethylammonium phenyltrialkylborate salts by the addition of alkyllithium reagents to a triorganylborane or organoboranylhalides

“…The method of borate salts synthesis using alkyllithium reagents is similar to that published by Neckers and co-workers [26,27]. Tetramethylammonium phenyltrimethylborate (B5) and tetramethylammonium phenyltriisopentylborate (B9) were prepared from the reaction of dichlorophenylborane with methyllithium followed by cation exchange.…”

“…Simple synthetic procedures have been developed to prepare suitably substituted stable phenyltrialkylborate tetramethylammonium salts [26,27]. The synthetic approaches that have been applied are outlined below and are based on the addition of alkyl or phenyllithium reagents to a triorganylborane or organoboranylhalides.…”

“…There are only a few examples of synthesis and application of other tetravalent borates [26]. This prompted the synthesis and the systematic study of phenyltrialkylborate salts in an attempt to understand the photophysical properties and structureeproperty relationships in these compounds.…”