Effect of the Steric Hindrance and Branched Substituents on Visible Phenylamine Oxime Ester Photoinitiators: Photopolymerization Kinetics Investigation through Photo‐DSC Experiments
Zhong‐Han Lee, Tung‐Liang Huang, Fatima Hammoud, Ching‐Chin Chen, Akram Hijazi, Bernadette Graff, Jacques Lalevée, Yung‐Chung Chen
Abstract
In this work, free radical photopolymerization (FRP) kinetics for series of different phenylamine oxime ester structures (DMA-P, DEA-P, DMA-M, TP-2P, TP-2M and TP-3M) was investigated. Steric hindrance and branched substituents were prepared to realize the corresponding electronic and photopolymerization effects. The photophysical, electrochemical, thermal properties and radical concentration were investigated by UV-visible spectroscopy, cyclic voltammetry (CV), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR). Furthermore, the structure-reactivity relationships were also studied in detail through photo-DSC experiment. We demonstrate that the introduction of alkyl chains and/or numbers of oxime esters affects significantly the photoreactivity. Under the same weight ratio of formulation and irradiated condition, TP-3M containing three oxime esters in its structure and methyl group in the periphery exhibits the highest double-bond conversion efficiency. TP-3M-based formulation also shows a wide operation window under different contents and light intensities. Importantly, the photoreactivity of the TP-3M-based system was found to be better than the commercial photoinitiator (OXE-01) under LED@405 nm at a low concentration. This work could provide some significance to the design of oxime esters with enhanced photoreactivity.