Multifunctional monomeric and polymeric photoinitiators for free radical photopolymerization

Abstract

In this study, novel polymerizable, polymeric and branched photoinitiators (PIs) were synthesized to attain high polymerization efficiency, migration stability, visible light absorption and water solubility to address environmental concerns. The photochemical and photophysical properties and photoinitiation mechanisms were investigated by electron-spin resonance, laser flash photolysis and steady-state photolysis techniques, as well as theoretical calculations. The performance of the photoinitiators was demonstrated for (photo)polymerizations of commercial monomers such as poly(ethylene glycol) diacrylate and 2-hydroxyethyl methacrylate. The first part of this thesis describes synthesis of novel thioxanthone and (bis)phosphonate functionalized poly(ethylene imine)s (PEI, Mw = 1800 g/mol) which can take part in dual curing process; in the first stage as the nucleophile and base for an aza-Michael reaction with acrylates, in the second stage as a photoinitiator in conjunction with iodonium salt (Iod). Also, charge transfer complexes (CTCs) formed between amines (PEI) and Iod can lead to free radical polymerization with or without irradiation in both stages. The second part describes two oligomeric photoinitiators prepared by integrating benzophenone (BP) alone or BP and phosphonate functionalities onto the oligo(amido amine) backbone. These PIs can generate radicals by CTC formation and by Type II photoinitiation at the same time under visible irradiation. The third part reports synthesis of a both polymeric and polymerizable PI, the first poly(-amino ester)- based PI, by the aza-Michael reaction of poly(ethylene glycol) diacrylate and 2-(2-aminoethoxy)-9H-thioxanthen-9-one. In the last part of this thesis, a cyclopolymerizable photoinitiator containing two Irgacure 2959 groups was synthesized by esterification reaction between 2,2’- (oxybis(methylene))diacrylic acid and Irgacure 2959. Its cyclic copolymer with di(tert-butyl) 2,2′-[oxybis(methylene)]bis(2- propenoate) was prepared by thermal polymerization.