Coumarins as Powerful Photosensitizers for the Cationic Polymerization of Epoxy-Silicones under Near-UV and Visible Light and Applications for 3D Printing Technology.

Mira Abdallah,Akram Hijazi,Frédéric Dumur,Jacques Lalevée

doi:10.3390/molecules25092063

Abstract

In this study, eight coumarins (coumarins 1–8) are proposed as near-UV and blue light sensitive photoinitiators/photosensitizers for the cationic polymerization (CP) of epoxysilicones when combined with 4-isopropyl-4’-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (IOD). Among these coumarins, four of them (coumarins 1, 2, 6 and 8) have never been reported in the literature, i.e., these structures have been specifically designed to act as photoinitiators for silicones upon near UV and visible irradiation. Good final reactive epoxy function conversions (FCs) and also high rates of polymerization (Rp) were achieved in the presence of the newly proposed coumarin-based systems. The polymers generated from the photopolymerization of epoxysilicones can be considered as attractive candidates for several applications such as: elastomers, coatings, adhesives, and so on. The goal of this study focuses also on the comparison of the new proposed coumarins with well-established photosensitizers i.e., 1-chloro-4-propoxythioxanthone (CPTX), 9,10-dibutoxyanthracene (DBA) or some commercial coumarins (Com. Coum). As example of their high performance, the new proposed coumarins were also used for laser write experiments upon irradiation with a laser diode at 405 nm in order to develop new cationic 3D printing systems.

Highlights

Photopolymerization processes can occur via a radical process or an ionic process
Cationic photopolymerization processes are insensitive to oxygen and low shrinkage is observed during the cationic process
The two-component coumarin/isopropyl-4’-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (IOD) (0.05%/1% w/w) photoinitiating systems are very efficient to initiate the cationic polymerization (CP) under air where very high final functional conversions (FCs) and high rates of polymerization (Rp) were achieved i.e., function conversions (FCs) = 55% for coumarin

Summary

Introduction

Photopolymerization processes can occur via a radical process or an ionic process. Photopolymers generated by the radical processes are usually characterized by high curing rates and often high rigidity. This type of polymerization suffers from the oxygen inhibition issue and from a rather high shrinkage during the polymerization process [1,2]. Cationic photopolymerization processes are insensitive to oxygen and low shrinkage is observed during the cationic process. Lower curing rates are generally observed for this second type of polymerization process [3,4,5,6]. Light-induced cationic polymerization processes are more and more interesting for industry [7,8]

Methods

Results

Conclusion