Dynamic mechanical analysis of two crosslinked copolymer systems.
OBJECTIVE
This research investigated the dynamic mechanical properties of two model dental restorative copolymers to elucidate the influence 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 fractions (0, 5, 10, 20, 40, 60, 80 and 100%) of a difunctional monomer [triethylene glycol dimethacrylate (TEGDMA)], resulting in two different copolymer systems (TMMA and TEEM). Bar-shaped specimens were heat-cured and tested for their dynamic mechanical properties at a fixed frequency (1Hz): flexural storage modulus and loss factor. Transition temperatures associated with peaks were determined using tan delta, phase angle and loss factor. The properties of one specimen were also examined using a range of applied frequencies.


RESULTS
Below the Tg, all resin systems had similar storage moduli. An increase in pendent group length lowered transition temperatures and demonstrated greater influence on temperature changes than did a change in crosslinker content. With increasing crosslinker, the transition temperatures increased. The values ascribed to transition temperatures were dependent upon the analysis method used: tan delta gave highest values, followed by phase angle, with loss factor values the lowest. Storage and loss moduli values and their ratio increased with increasing frequency of applied signal. Loss factor analysis provided the most elucidation of sub-Tg transitions.


CONCLUSIONS
Restorative polymers with specific desired physical and mechanical properties can be achieved by both judicious selection of monomer structure as well as by the controlled addition of the crosslinking agent.
D000704:Analysis of Variance; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003432:Cross-Linking Reagents / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D004055:Differential Thermal Analysis; D004548:Elasticity; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008768:Methylmethacrylates / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014783:Viscosity
D003432:Cross-Linking Reagents; D003764:Dental Materials; D008689:Methacrylates; D008768:Methylmethacrylates; D011109:Polymethacrylic Acids; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; C029263:2-ethoxy ethyl methacrylate