Photopolymerization of 2‐hydroxyethyl methacrylate: Effect of the medium properties on the polymerization rate

Abstract

The effect of solvent properties on the polymerization rate of 2-hydroxyethyl methacrylate (HEMA) was examined with the photoreaction of 4,4Ј-azobis(2amidinopropane) and photoinduced electron transfer of a thioxanthone derivative and triethanolamine as the radical source. The polymerization rate of HEMA was markedly affected by pH and the medium polarity. The rate increased over a pH range of 6 -8. The dependence of the polymerization rate on the amine concentration photoinitiated by the bimolecular system was different in water and acetonitrile as solvents. In aqueous medium, pH 9.5, the rate increased with the amine concentration reaching a constant value at 0.025 M amine; further amine addition inhibited the polymerization. In organic media the inhibition effect was not observed. Triethanolamine addition did not change the polymerization rate photoinitiated by the azo compound. Photochemical studies of the thioxanthone were carried out under the polymerization conditions. These studies allowed us to simulate the dependence of the polymerization rate on the amine concentration. The results are explained in terms of the interaction of the ketone excited states with the amine in the different media.

Photoinitiated Polymerization of 2-Hydroxyethyl Methacrylate by Riboflavin/Triethanolamine in Aqueous Solution: A Kinetic Study

“…The rate-pH profiles for the polymerization of HEMA at 1–3 M concentrations are shown in Figure 1. These indicate an enhancement in the rate, with pH, in the range of 6.0–9.0, as observed earlier by Valdebenito and Encinas [27]. This increase in the rate of polymerization, with pH, is attributed to the presence of a labile proton on the hydroxyl group of HEMA [39].…”

“…Therefore, the rate of reaction would be controlled by solute diffusion and hence the degree of redox reactions occurring between the species involved in a particular medium. A small change in the viscosity of HEMA solutions with an increase in pH has been reported [27]. Thus, the HEMA concentration appears to be one of the controlling factors in the rate of polymerization.…”

“…In most cases, the polymerization rates of HEMA have been determined dilatometrically [13–15]. This method has been used to study the effect of solvent on the rates of polymerization of HEMA photoinitiated by azo compounds [26, 27], camphorquinone [28, 29], and pyrene derivatives [30]. In this work, we report a study of the approximate measure of the kinetics of polymerization of HEMA initiated by RF/TEOHA system under visible light using a spectrophotometric method for the assay of HEMA during the reactions.…”

Thioxanthone‐Based Hydrophilic Visible Photoinitiators for Radical Polymerization

“…Back electron transfer procedure is a term often used to indicate thermal reversal of the excited state electron transfer restoring the donor and acceptor in their original oxidation level . It may lead the photoinitiator to keep its structure . Upon visible light excitation of the n–π* transition, the generation of the triplet was very fast in aqueous solution (presumably as fast as in homogeneous solution) .…”

A thioxanthone‐based visible photoinitiator

“…The spectrum shows two peaks at 680 and 380 nm. The peak at 680 nm was assigned to the triplet–triplet absorption of TX‐MPM based on similarities with the triplet–triplet spectra of TX and its derivatives 10, 11, 37, 44–46. Figure 7(c) shows the decay kinetic of the transient absorption at 680 nm.…”