High-temperature high-pressure polymerized urethane dimethacrylate-mechanical properties and monomer release

This study was conducted to determine selected mechanical/physical properties of and monomer release from high-temperature high-pressure (HT/HP) polymerized urethane dimethacrylate (UDMA).

Flexural strength (σf), hardness, fracture toughness (KIC), and density (ρ) were determined for five UDMA resin blocks produced via different polymerization protocols. High performance liquid chromatography (HPLC) was used to determine monomer release from the five polymers. One way ANOVA, Scheffé multiple means comparisons (α=0.05), and Weibull statistics (for σf) were used to analyze the results.

The results showed that HT/HP polymerization resulted in a significant (p<0.05) increase in σf and ρ, along with an increase in Weibull modulus. No significant differences were found in hardness and KIC between the two HT/HP polymerized materials. A significantly lower (p<0.05) monomer release was detected for the HT/HP polymerized groups.

The results of this study suggest that HT/HP polymerization affects the network structure and leads to UDMA polymers with improved mechanical/physical properties and with dramatically reduced monomer release. The low elution of monomers from HT/HP and HP polymerized materials suggests the achievement of a higher degree of conversion and a lesser degree of inhomogeneity with regards to microgel domains. The results, however, cannot fully explain the dramatic increase in mechanical/physical properties reported previously for RCB, improvements that may be due to a better filler-matrix interaction afforded by HT/HP polymerization.