Photopolymerization kinetics of dimethacrylate‐based light‐cured dental resins

Abstract

ABSTRACT:The influence of certain factors [structure and concentration of tertiary amines as coinitiators, monomer composition, presence of inorganic pigments, and incident light intensity (I 0 )] on the polymerization rates (R p ), polymerization quantum yields, and conversions of bisphenol A-bis(glycidyl methacrylate) (Bis-GMA)/triethylene glycol dimethacrylate based resins was studied. The initial rate of bulk polymerization increased and the final conversion decreased with the content of Bis-GMA in the mixture. In contrast, it was established that, for all monomer compositions, the R p grew when increasing the I 0 , the R p being directly proportional to the square root of I 0 . Such behavior is in agreement with the well-known kinetic expression for the ideal radical photoinitiated polymerization in solution of monofunctional monomers, in spite of the complexity of the dimethacrylate mixtures that were studied. Both the structure and the concentration of reducing amine affected the efficiency of the initiator system and therefore the kinetic behavior of polymerization of these formulations under irradiation. The rate of polymerization increased with the increase of coinitiator concentration over the interval of 0 -1%, but later it diminished when increasing the amine content, suggesting that the excess coinitiator retards the polymerization process. The study of the photoreduction of camphorquinone in the presence of different amines showed that the efficiency of the coinitiator depends not only on its ability to photoreduce camphorquinone, forming amine-derived radicals, but also on the reactivity of these radicals toward the initiation of acrylic monomer polymerization.

Efficiency of 2,2‐dimethoxy‐2‐phenylacetophenone for the photopolymerization of methacrylate monomers in thick sections

“…CQ produces free radicals on exposure to 450-500 nm radiation and this process is activated by the redox reaction with tertiary amines. [1][2][3][4][5][6] CQ is the most common photoinitiator but it possesses a noticeable yellowish color. For the majority of restorative work this is not an issue as natural tooth color also has a yellowish hue, but for cosmetic restoration this yellow color can be a significant factor.…”

Coupled UV–Vis/FT–NIR Spectroscopy for Kinetic Analysis of Multiple Reaction Steps in Polymerizations

“…45,65 It is well-known that absorbance spectra, and thus I abs , depend on the electronic and resonance characteristics of the solvent (confirmed in Figure S3). Hence, obtaining I abs in the actual polymerizing medium provides an unparalleled advantage over other analytical methods.…”

Influence of viscosity and amine content on CC conversion and color stability of experimental composites

“…Otherwise, the materials did not differ statistically among themselves in DC for amine concentrations above 1 mol% (1:2). Previous studies have demonstrated that the efficiency of radical generation has a direct influence on polymerization efficiency [6,8]. These results are related to the fact that sufficient amine is necessary to act as hydrogen donor for CQ and start the polymerization process, but, on the other hand, above certain limits, any amine co-initiator may act as a retarder because an excess of amine may trap initiating radicals by termination reactions [25].…”

“…Therefore, factors such as CQ and amine concentrations, their ratio, molecular structure of the amine, and reactivity of the formed radicals to initiate monomer polymerization, all play important roles on the polymerization reaction properties of the resulting polymer [3,6,7]. Although a direct correlation between co-initiator concentration and polymerization efficiency might be considered, it is known that above certain concentration limits, amines may act as retarders since excess amine may trap initiating radicals by termination reactions [6,8]. Excess amine might also cause color instability because of the eventual formation of oxidative products [9][10][11].…”