Dynamic mechanical analysis of high pressure polymerized urethane dimethacrylate

ObjectivesThe aim of this study was to compare the viscoelastic properties of high pressure (HP) polymerized urethane dimethacrylate (UDMA) with those of control, ambient pressure thermo-polymerized and photo-polymerized, UDMA and to assess the effect of varying polymerization parameters (protocol, temperature, and initiator) on the viscoelastic properties of HP polymerized UDMA.MethodsThe viscoelastic properties of the two control polymers, polymerized under atmospheric pressure, and four experimental polymers, polymerized under HP, were determined via dynamic mechanical analysis (DMA), in three point bending configuration. Atomic force microscopy (AFM) was used to characterize fractured polymer surface morphologies.ResultsThe results showed that: HP-polymerization lead to a polymer with significantly higher Tg and E′rub, indicative of a higher crosslink density; modifying the polymerization protocol resulted in a significant increase in tan δ; increasing the polymerization temperature lead to a significant decrease in E′rub and Tg; and that the polymer with no initiator had the lowest E′, E″, Tg, and E′rub and the highest tan δ, suggesting that under this conditions a polymer with significantly reduced crosslink density had been obtained. A characteristic nodular appearance was seen for the two control polymers under AFM, while a modified surface morphology was present in the case of HP polymerized materials.SignificanceThe DMA results suggest that polymerization under HP resulted in polymers with an increased crosslink density and that the higher polymerization temperature or the lack of initiator was detrimental to the viscoelastic properties determined. Changes in polymer network morphology were identified by AFM characterization.