Factors affecting the sensitivity to acid inhibition in novel acrylates characterized by secondary functionalities

Abstract

Here we demonstrate that acrylates exhibit significant rate reductions in the presence of small concentrations of protic acids (0.1–0.5 wt %) compared with the bulk monomer concentration. Dramatically different sensitivities to acid inhibition, differing by up to 2 orders of magnitude, are exhibited for various acrylates. This study examines the various factors that cause enhanced sensitivity toward acid inhibition in novel acrylates characterized by carbamate and cyclic carbonate secondary functionalities. Acid inhibition studies conducted in the presence of a highly polar solvent, such as propylene carbonate, have been performed to determine the impact of overall medium polarity and the extent of acid dissociation on the sensitivity to acid inhibition. The studies depict only a twofold increase in the parameters associated with acid inhibition, upon the addition of 70 wt % propylene carbonate, in comparison with an increase of 2 orders of magnitude for the novel acrylates. These studies indicate that the susceptibility to acid inhibition is primarily determined by the stability of the hypothesized radical–acid complex as well as its propensity to terminate with other species in the system and not by the extent of acid dissociation in the system. Furthermore, it is implied that the stability of the radical–acid complex and its propensity to terminate with other species in the system are dominated by intramolecular interactions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1287–1295, 2007

Development of quantitative structure–activity relationships for explanatory modeling of fast reacting (meth)acrylate monomers bearing novel functionality

“…Using a B3LYP/6-31G* basis they computed a negative charge for their modeled propagating radical, thus suggesting that the propagating species may have some negatively charged character. The anionic nature of the propagating species was further investigated by Bowman who found a significant inhibition by strong acid when polymerized under photoinitiated radical conditions [27]. Thus, it appears that there is a Michael addition component to the polymerization that is occurring at the acrylate functional group and this idea is supported by our findings.…”

“…That this is possible for the carbamate bearing monomers suggests that the descriptor functions to differentiate the faster carbamate acrylate monomers from the generally slower traditional acrylates. The importance of a contribution of electron density by the nitrogen to the carbamate carbonyl correlation speaks to the results of Kilambi for the acid inhibition of acrylates bearing novel functionalities, including carbamate and cyclic carbonate [27]. As the nitrogen of the carbamate donates electron density to the carbonyl group, the build-up of negative charge on the oxygen atom makes it a site for intermolecular hydrogen bonding, as well as a site for protonation under acidic conditions.…”

Evaluation of highly reactive mono-methacrylates as reactive diluents for BisGMA-based dental composites

“…Recently a series of mono-vinyl (meth)acrylic monomers characterized by unique secondary moieties and greatly enhanced polymerization kinetics has been developed. The secondary moieties include, carbamates, carbonates, cyclic carbonates, cyclic acetals, hydroxyl/carboxy, oxazolidones, morpholine, and aromatic rings [11][12][13][14][15][16][17][18][19][20]. The cure rates of these mono-vinyl acrylates and methacrylates rival or exceed those of multifunctional acrylates while also achieving much higher extents of cure, hence reducing the amount of extractable material [13].…”

Influence of the secondary functionality on the radical‐vinyl chemistry of highly reactive monoacrylates

“…The exact reasons for the enhancement in reactivity have been elusive to date 3, 14–17. The copolymerization ratios of the acrylates with other monomers were observed to be altered upon incorporation of the secondary functionalities,18 and kinetic studies to investigate the mechanisms responsible for enhanced reactivity revealed that the addition of the secondary functionality alters the polymerization behavior by impacting the radical‐vinyl chemistry in these systems 18–20. A series of Michael addition reactions,21, 22 has previously been conducted on acrylic and methacrylic monomers incorporating carbamate, N ‐acyl carbamate, carbonate and cyclic carbonate functionalities 23.…”