Development of methacrylate/silorane hybrid monomer system: Relationship between photopolymerization behavior and dynamic mechanical properties

Abstract

Resin chemistries for dental composite are evolving as noted by the introduction of silorane-based composites in 2007. This shift in the landscape from methacrylate-based composites has fueled the quest for versatile methacrylate-silorane adhesives. The objective of this study was to evaluate the polymerization behavior and structure/property relationships of methacrylate-silorane hybrid systems. Amine compound ethyl-4-(dimethylamino) benzoate (EDMAB) or silane compound tris(trimethylsilyl) silane (TTMSS) was selected as coinitiators. The mechanical properties of the copolymer were improved significantly at low concentrations (15, 25, or 35 wt %) of silorane when EDMAB was used as coinitiator. The rubbery moduli of these experimental copolymers were increased by up to 260%, compared with that of the control (30.8 ± 1.9 MPa). Visible phase separation appeared in these formulations if the silorane concentrations in the formulations were 50–75 wt %. The use of TTMSS as coinitiator decreased the phase separation, but there was a concomitant decrease in mechanical properties. In the neat methacrylate formulations, the maximum rates of free-radical polymerization with EDMAB or TTMSS were 0.28 or 0.06 s−1, respectively. In the neat silorane resin, the maximum rates of cationic ring-opening polymerization with EDMAB or TTMSS were 0.056 or 0.087 s−1, respectively. The phase separation phenomenon may be attributed to differences in the rates of free-radical polymerization of methacrylates and cationic ring-opening polymerization of silorane. In the hybrid systems, free-radical polymerization initiated with EDMAB led to higher crosslink density and better mechanical properties under dry/wet conditions. These beneficial effects were, however, associated with an increase in heterogeneity in the network structure.

Self-strengthening hybrid dental adhesive via visible-light irradiation triple polymerization

“…These results are evidence that the condensation reaction between silanol-silanol and/or silanol-hydroxyl groups occurred gradually with storage time. In addition to the free radical promoted cationic ring-opening polymerization 32, 33 , a decrease of the band at 884 cm −1 attributed to the epoxy group, was visible in the FTIR spectrum (Figure 2D). These results provide evidence that epoxy ring-opening occurred concomitantly with the free radical polymerization and sol-gel process.…”

“…The initiation mechanism triggered by visible light irradiation and the polymerization mechanisms are also demonstrated in Scheme 1. The Brønsted acid has been used to initiate the cationic polymerization of epoxy or vinyl ether monomers to prepare interpenetrating polymer network (IPN) structure 32, 33, 49 . Here, the generated photoacid is utilized to catalyze the sol-gel reaction of the methoxysilyl function and initiate the cationic ring-opening polymerization of the epoxide group.…”

“…Methacrylic double bond conversion was monitored by the band ratio profile-1637 cm −1 (C=C)/1608 cm −1 (phenyl). Epoxy group conversion was followed by monitoring the intensity of the peak at 884 cm −1 32 . The calculation method to get the epoxy group conversion was used based on the published paper 38–41 .…”

“…Silorane-based composite has been developed and the polyether structure exhibits strong mechanical and thermal properties, chemical resistance, and low shrinkage compared with methacrylate-based materials 30, 31 . Recently, we have studied the methacrylate/silorane hybrid adhesive systems 32 . The results indicated that the crosslink density of dental adhesives was improved with the addition of silorane monomers, and the degree of conversion of epoxy groups was affected by the number of functionalities 33 .…”

Mimicking nature: Self-strengthening properties in a dental adhesive

“…CQ (1.0 wt%), EDMAB(1.0 wt%), and OPPIH (2.0 wt%) were used as photoinitiator (PI) systems with respect to the total amount of monomers [39]. The chemical structures of monomers and PI are shown in Scheme 1.…”