title: Dynamic mechanical analysis of high pressure polymerized urethane dimethacrylate.
abstract: OBJECTIVE
  The 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.
  
  
  METHODS
  The 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.
  
  
  RESULTS
  The 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 tanδ; 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 tanδ, 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Laboratoire de biomatériaux dentaires, Faculté de chirurgie dentaire, Université de Lille 2, Lille, France. Electronic address: pascal.behin@free.fr.
authors.forename: Pascal
authors.initials: P
authors.lastname: Béhin
authors.affiliation: Unité Matériaux Et Transformations, CNRS UMR 8207, Université Lille 1 Sciences et Technologies, 59655 Villeneuve d'Ascq, France.
authors.forename: Grégory
authors.initials: G
authors.lastname: Stoclet
authors.affiliation: Faculty of Dentistry, The University of British Columbia, Vancouver, Canada.
authors.forename: N Dorin
authors.initials: ND
authors.lastname: Ruse
authors.affiliation: Unité de Recherches Biomatériaux innovants et interfaces (URB2I-EA-4462), Faculté de chirurgie dentaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
authors.forename: Michaël
authors.initials: M
authors.lastname: Sadoun
mesh_terms: D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D058105:Polymerization; D011140:Polyurethanes / Q000737:chemistry*; D011312:Pressure
chemical_list: D008689:Methacrylates; D011140:Polyurethanes; C029824:urethane dimethacrylate luting resin
keywords: Atomic force microscopy; Dynamic mechanical analysis; High pressure polymerization; Polymers