Studies on polyfunctional cyclophosphazene monomers for dental use (2)--physical properties of polymers.

The present studies were aimed at the development of monomers for dental resins, for which the authors substituted the 8 Cl atoms in P4N4Cl8 with hydrophobic groups (Ph, TF and OF) and a polymerizing group (EMA), and bulk-polymerized them in order to examine their physical properties. Attention was focused on the relationship between the number of substituted hydrophobic groups and the mechanical properties, thermal expansion coefficient, polymerization shrinkage, contact angle, refractive index, water sorption and solubility to establish a basis for the practical use of cyclophosphazene monomers as dental resin monomers. The results obtained were as follows : compressive strength, transverse strength and hardness under dry conditions decreased in accordance with the increased number of substituted hydrophobic groups, but their degree of decrease in mechanical strength under wet conditions (after immersion in water) was small, proving that in comparison with PNC-EMA 4006, having no hydrophobic group, the mechanical properties under wet conditions were improved. It was found that by hydrophobic group substitution, contact angle increased and water sorption decreased. On the other hand, thermal expansion coefficient increased in accordance with the number of substituted hydrophobic groups, but polymerization shrinkage in all cases was very small, 3.09-9.08 vol%. Solubility also showed low values, 0.0530.160 wt% when the number of substituted hydrophobic groups was 1-2.