Synthesis and performances of polysiloxane-modified 5-arylthianthrenium salt cationic photoinitiators with self-floating capability

Abstract

Currently cationic photoinitiators possess undesirable characteristics of poor solubility in epoxy resins and the release of odorous and toxic by-products. These shortcomings greatly limit the applications of the photoinitiators. Here, the synthesis and initiating cationic photopolymerization properties of three new polysiloxane-modified 5-arylthianthrenium salt cationic photoinitiators (1187-Si-A/B/C) whose polysiloxane-modified cations could be considered as environmentally friendly are reported. The photoinitiators are synthesized based on 9-(4-hydroxyethoxyphenyl) thianthrenium hexaflorophosphate (Esacure 1187) and polysiloxane. The cationic photoinitiators not only exhibit excellent solubility in epoxy resins, but also do not release odour and toxic by-products under UV irradiation, which is demonstrated by liquid chromatography-electrospray ionization-mass spectrometry [LC-ESI(+)-MS]. The photoinitiating activity of 1187-Si-A/B/C is investigated by real-time infrared spectroscopy (RTIR), and it is found that 1187-Si-A/B/C can effectively initiate cationic photopolymerization by the photosensitization of 9,10-dibutoxyanthracene (DBA). More importantly, the polysiloxane chains offer 1187-Si-A/B/C good self-floating capability, and thus the photoinitiators are promising for the preparation of gradient polymers by cationic photopolymerization.