Zirconocenes as Photoinitiators for Free-Radical Polymerisation of Acrylates

Abstract

This paper reports the photochemical behaviour of unbridged (1−6) and bridged zirconocenes (7r, 7m), whose substituents differ in both electron-donor and steric properties. The study of the electronic spectra and EPR spin-trapping experiments showed the photogeneration of ligand-and zirconium-centred radicals at wavelengths higher than 350 nm. This feature makes these complexes suitable as photoiniti-

Zirconium complexes to overcome oxygen inhibition in free‐radical photopolymerization of acrylates: Kinetic, mechanism, and depth profiling

“…In addition, we observed during the course of the experiments that ZrPro, BCPZr, and DMAZr lead to limited pot‐life: a precipitate could be observed after few hours for BCPZr and after 1 day for ZrPro and DMAZr. This may be attributed to the sensitivity of such compounds to humidity and the nature of the medium, explaining the lack or low reactivity of these compounds 28. By contrast, TEAZr was found to be quite stable in the monomer.…”

Photochemistry of tris(pyrazolyl)borate titanium(IV) complexes

“…This observation and the fact that Cl ! Ti transitions occur at higher energy [9][10][11], indicate that the band at 315 nm for 1 and at 328 nm for 2 can reasonably be assigned, respectively, to Tp ! Ti and Tp* !…”

Radical Mechanisms in the Metallocenes

“…These spin traps include N-tert-butyl-α-phenylnitrone (PBN), nitrosodurene (ND), and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) [24,25]. According to the NIEHS Spin Trap Database [24,25], the hyperfine coupling constants (hfcc) of the spin adducts detected can be attributed to the cyclopentadienyl type radicals [26]. Therefore, the primary photochemical act can be described by Figure 12.…”

“…In order to test the effectiveness of these organometallic photoinitiators, Similar EPR/spin trapping experiments were carried out in the presence of different alkenes such as 1-pentene, methyl methacrylate (MMA) and tert-butyl acrylate (tBA) and in different solvents such as benzene and dichloromethane. During irradiation of the zirconocene/alkene mixtures, the growth of the EPR signal of a carbon-centred radical was detected [26].…”