Jacques Cavezzan

Synthesis, reactivity, and properties of new diaryliodonium salts as photoinitiators for the cationic polymerization of epoxy silicones

Diaryliodonium tetrakis (pentafluorophenyl) borate salts generate a higher reactivity than any other known diaryliodonium salt. The photochemical properties of diaryliodonium tetrakis (pentafluorophenyl) borate salts were compared to those of the diaryliodonium hexafluoroantimonate salt. The results show that these new salts are the most reactive photoinitiators in this family. In addition, diaryliodonium tetrakis (pentafluorophenyl) borate salts are soluble in low polarity media, such as epoxy silicone oils, which are rich in epoxy groups and insensitive to humidity. These salts have the advantage not to contain a heavy metal (such as antimony). The new properties generated by the use of the tetrakis (pentafluoropheyl) borate anion make the future of the cationic photopolymerization promising.

Photo-oxidation of polydimethylsiloxane oils: II—Effect of vinyl groups

Abstract The photo-oxidations, at wavelengths longer than 300 nm, of polydimethylsiloxane (PDMS) oils with various contents of vinyl and different configurations (vinyl in the polymer chain (3·1 and 7·1 wt % vinyl) or at the end of the chain of a low-molecular-weight compound (29 wt % vinyl)) have been examined. During irradiation, in the presence of oxygen, competition between scission and oxidation reactions occurs. Chain scissions represent the main reaction as expected from GC-MS analysis of a low-molecular-weight compound oxidation and from the evaluation of oxidized products, which represent only about 20% of the consumption of vinyl groups. The main oxidation products detected by FTIR spectroscopy are silanol (3475 cm −1 ), carboxylic acids (1717–1724 cm −1 ) and ester (1737 cm −1 ). An oxidation mechanism based on a radical addition to the double bond as initiation process is proposed to explain the formation of oxidized groups.

Photo-oxidation of polydimethylsiloxane oils: Part I—Effect of silicon hydride groups

Abstract Photo-oxidations at wavelengths longer than 300 nm of polydimethylsiloxane (PDMS) oil with various contents of SiH and different configurations (H inside the chain (2·2 H equivalent kg−1) or at the end of the chain (1·2–4 and 15 H equivalent kg−1)) have been examined. Hydroperoxides groups are primarily formed on photo-oxidation and result from radical attack on the SiH bond. These photo-unstable and thermally unstable hydroperoxides are transformed essentially into silanols, absorbing at 3300 cm−1. Oxygen consumption measurements suggest a 1 1 stoichiometry between SiH and oxygen consumed, whereas the quantitative determination of SiOH reveals a deficit, mainly as a result of a condensation reaction which leads to a significant increase in viscosity.

Photo-oxidation of polydimethylsiloxane oils Part III—effect of dimethylene groups

Abstract Photo-oxidations at wavelengths longer than 300 nm of polydimethylsiloxanes (PDMS) formed by hydrosilylation reactions (i.e. containing dimethylene (∼CH2CH2∼) and methine groups) have been examined. The consumption of initial functional groups and the appearance of new groups derived from the photo-oxidation were followed by FTIR, 1H, 13C and 29Si NMR and GC/MS. The main photo-oxidation process is the hydroperoxidation of dimethylene groups and the photoscission of hydroperoxide groups into β-silylated carboxylic acid (∼SiCH2COOH) and silanol groups (SiOH). A small part of the silanols formed is condensed into ester and siloxane groups.

Photooxidation of polydimethylsiloxane oils and resins. IV—effect of phenyl groups

Abstract Photooxidations at wavelengths longer than 300 nm of polydimethylsiloxane (PDMS) containing various contents of MePh and Ph 2 groups have been examined, both in the case of linear and crosslinked silicones. FTIR, UV and fluorescence spectroscopies reveal a slow photooxidation involving both scission and oxidation of the phenyl ring. No significant yellowing can be associated with the presence of the phenyl ring except in the case of short wavelength irradiation.