Influence of chain extender length of aromatic dimethacrylates on polymer network development.

Objective: To investigate the role of chain extender size from Bis-EMA monomers on the polymerization profiles and properties of the crosslinked polymers. Additionally, the influence of Bis-GMA was also evaluated.
Methods: The polymer network from homopolymers Bis-EMA4, Bis-EMA10 and Bis-EMA30 was characterized, as well as copolymers formed among these monomers and Bis-GMA. The degree of conversion from neat and blended monomers as a function of photo-activation time was evaluated by FTIR. Rate of polymerization, network parameter and cross-link density from materials were demonstrated. Water sorption and solubility were determined according to ISO 4049 specification and the data obtained were analyzed by two-way ANOVA/Tukey's test (alpha=0.05). Flexural strength and Young's modulus from polymerized monomers/co-monomers were measured after 24h water storage at 37 degrees C and the results were analyzed by one-way ANOVA/Tukey's test (alpha=0.05).
Results: Monomers with larger ethylene oxide units presented the highest values regarding the degree of conversion and cross-link density. The effect of the chain extender length was also observed in water sorption and solubility polymer characteristics, with Bis-EMA4 being the most hydrophobic polymer. Bis-EMA10 and Bis-EMA30 homopolymers were not able to be tested with the three point bending test due to their great flexibility. The addition of Bis-GMA produced stronger and more rigid Bis-EMA polymers (p<0.05).
Significance: Aromatic dimethacrylates with different chain extender lengths can be a useful alternative in controlling the properties of a dental material, adjusting those to specific applications.