title: Optimum pressure for the high-pressure polymerization of urethane dimethacrylate.
abstract: OBJECTIVE
  The aim of this study, part of our research to improve properties of resin composite blocks suitable for CAD/CAM and to better understand underlying mechanisms associated with high-temperature/high-pressure (HT/HP) polymerization, was to determine an optimum polymerization pressure of urethane dimethacrylate (UDMA) in the presence of an initiator (0.5% benzoyl peroxide) by determining the degree of conversion (DC) and viscoelastic properties of polymers obtained at 90°C under varying HP.
  
  
  METHODS
  DC and viscoelastic properties of 16 UDMA polymers, two controls (thermo-cured and thermo-cured followed by post-cure relaxation) and 14 experimental groups (HP polymers, in the range of 50-350 MPa, in 50 MPa increments, without and with post-cure relaxation) were determined via near infrared spectroscopic analysis and dynamic mechanical analysis, respectively.
  
  
  RESULTS
  The results have shown that HP UDMA polymers have DC superior to that of the control group. With regards to E' and E″, the results have shown no significant difference between control and HP polymers. The damping factor, tanδ, decreased with increasing pressure, while E'rub and Tg increased. Polymerization at 150 MPa or higher resulted in significantly higher E'rub and Tg.
  
  
  CONCLUSIONS
  The results of this study suggested that HP polymerization at 90°C of UDMA reduced the number of defects and the free volume, leading to a more homogeneous polymer network. The results have also suggested that 200 MPa is an optimum polymerization pressure, resulting in polymers with significantly higher DC, E'rub, and Tg, while maintaining adequate damping capacity (tanδ).
authors: Unité de Recherches Biomatériaux innovants et interfaces (URB2I-EA-4462), Faculté de chirurgie dentaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
authors: Anh Chi
authors: AC
authors: Phan
authors: Laboratoire de biomatériaux dentaires, Faculté de chirurgie dentaire, Université de Lille 2, Lille, France.
authors: Pascal
authors: P
authors: Béhin
authors: UMET, Faculté de Sciences, Université de Lille 1, Villeneuve d'Ascq, France.
authors: Grégory
authors: G
authors: Stoclet
authors: Faculty of Dentistry, The University of British Columbia, Vancouver, Canada. Electronic address: dorin@dentistry.ubc.ca.
authors: N
authors: N
authors: Dorin Ruse
authors: UFR d'Odontologie, Université Paris Diderot, Paris, France.
authors: Jean-François
authors: JF
authors: Nguyen
authors: Unité de Recherches Biomatériaux innovants et interfaces (URB2I-EA-4462), Faculté de chirurgie dentaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
authors: Michaël
authors: M
authors: Sadoun
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D055119:Elastic Modulus; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry*; D058105:Polymerization; D011140:Polyurethanes / Q000737:chemistry*; D011312:Pressure; D013499:Surface Properties; D013696:Temperature
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011140:Polyurethanes; C029824:urethane dimethacrylate luting resin
keywords: Degree of conversion; Dynamic mechanical analysis; High-pressure polymerization; Polymers