Analysis of a dimethacrylate copolymer (bis-GMA and TEGDMA) network by DSC and 13C solution and solid-state NMR spectroscopy.

In this work the effect of dilution with TEGDMA on the kinetics of Bis-GMA polymerization and on the extent of polymerization or degree of conversion was studied using (a) DSC and (b) NMR. The systems with lower viscosity and lower Tg exhibited higher extent of polymerization. For Bis-GMA/TEGDMA mixtures the calculated Tg values were found to be higher than the experimental values suggesting that a dilution effect is predominant rather than intermolecular hydrogen bonding. Solid state NMR has been shown to be a convenient method for measuring the total amount of conversion in a mixed monomer system. The disappearance of the NMR solution spectrum was used to reveal overall polymerization kinetics.

Characterization of some aromatic dimethacrylates for dental composite applications.

Several novel dimethacrylates have been developed as alternative matrix materials for dental composite applications. For the cured bulk polymers the equilibrium water uptake, reduction of glass transition temperatures (Tgs) by water sorption, refractive indices and the surface hardness have been determined. The properties were then compared with those of the control Bis-GMA. These properties correlated well with the structures of the polymers. Polar groups were found to increase the water sorption and thus reduce surface hardness.

Structure property relationship among novel dental composite matrix resins.

Several novel dimethacrylate monomers of propoxylated diphenols have been synthesized to establish a correlation between their structure and the important properties of viscosity, curing shrinkage and wetting behaviour. These dimethacrylates were designed to possess linear and flexed structures. These new monomers exhibited very much lower viscosities compared to the conventionally used Bis-GMA. Good correlations were obtained for variations of the monomer structures with bulk viscosities and curing shrinkages. However, the wetting behaviour of these resins did not show any trend.

Influence of hydrogen bonding on properties of BIS-GMA analogues.

The influence of chemical structure on the important properties of composite matrix resins is being systematically investigated. This study addresses the relationships between pendent side chain structures, viscosity and curing shrinkage. In particular, viscosity is known to be greatly influenced by intermolecular interactions, such as hydrogen bonding, and free volume effects. In order to establish the relative importance of these factors, analogues of BIS-GMA were synthesized in which the pendent hydroxyl groups were replaced by trimethyl siloxyl, and by dimethyl, isopropyl siloxyl groups. The viscosities were determined with a cone and plate viscometer and curing shrinkages were determined gravimetrically. They were compared to previously determined values for BIS-GMA and its methyl and hydrogen substituted analogues. The high viscosity of BIS-GMA is drastically reduced by replacement of the hydroxyl group, or its substitution by silylation. The relatively smaller effects produced by varying the bulk of the substituted side chains indicates that the main effect on viscosity is due to the presence or absence of hydrogen bonding. Conversely, increasing the bulk of the side chain substituent has less effect on viscosity, but significantly reduces the curing shrinkage. Changes in curing shrinkages were explained in terms of effects of free volumes associated with the monomers.

Effect of dilution on the kinetics of cross-linking thermal polymerization of dental composite matrix resins.

The effect of dilution of 2,2-bis-(4-(2-hydroxy-3-methacryloxyprop-1oxy) phenyl) propane (bis-GMA) with triethylene glycol demethacrylate (TEGDMA) on the extent of polymerization, Ep, has been studied using differential scanning calorimetry. The isothermal and dynamic measurements indicate that the Ep is affected dramatically by dilution. The residual polymerization was also found to be strongly influenced by dilution. However, the apparent activation energy, Eapp, was found to be independent of dilution.