INFLUENCE OF HYDROGEN-BONDING ON PROPERTIES OF BIS-GMA ANALOGS

The influence of chemical structure on the important properties of com posite matrix resins is being systematically investigated. This study addresses the relationships between pendent side chain structures, vis cosity and curing shrinkage. In particular, viscosity is known to be g reatly influenced by intermolecular interactions, such as hydrogen bon ding, and free volume effects. In order to establish the relative impo rtance of these factors, analogues of BIS-GMA were synthesized in whic h 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 determine d gravimetrically. They were compared to previously determined values for BIS-GMA and its methyl and hydrogen substituted analogues. The hig h viscosity of BIS-GMA is drastically reduced by replacement of the hy droxyl group, or its substitution by silylation. The relatively smalle r 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 si de chain substituent has less effect on viscosity, but significantly r educes the curing shrinkage. Changes in curing shrinkages were explain ed in terms of effects of free volumes associated with the monomers.