DYNAMIC-MECHANICAL ANALYSIS OF 2 CROSS-LINKED COPOLYMER SYSTEMS

Objectives. This research investigated the dynamic mechanical properti es of two model dental restorative copolymers to elucidate the influen ce of pendent group length and addition of crosslinking agent. Methods . Two different monomethacrylate resins [(methyl methacrylate (MMA) or 2-ethoxyethylmethacrylate (EEM)] were added to Various molar fraction s (0, 5, 10, 20, 40, 60, 80 and 100%) of a difunctional monomer [triet hylene glycol dimethacrylate (TEGDMA)], resulting in two different cop olymer systems (TMMA and TEEM). Bar-shaped specimens were heat-cured a nd tested for their dynamic mechanical properties at a fixed frequency (1 Hz): flexural storage modulus and loss factor. Transition temperat ures associated with peaks were determined using tan delta, phase angl e and loss factor. The properties of one specimen were also examined u sing a range of applied frequencies. Results. Below the Tg, all resin systems had similar storage moduli. An increase in pendent group lengt h lowered transition temperatures and demonstrated greater influence o n temperature changes than did a change in crosslinker content. With i ncreasing crosslinker, the transition temperatures increased. The valu es ascribed to transition temperatures were dependent upon the analysi s method used: tan delta gave highest values, followed by phase angle, with loss factor values the lowest. Storage and loss moduli values an d their ratio increased with increasing frequency of applied signal. L oss factor analysis provided the most elucidation of sub-Tg transition s. Significance. Restorative polymers with specific desired physical a nd mechanical properties can be achieved by both judicious selection o f monomer structure as well as by the controlled addition of the cross linking agent.