title: Thermal behavior of poly hydroxy ethyl methacrylate (pHEMA) hydrogels.
abstract: The freezing and melting behavior of water in poly hydroxy ethyl methacrylate (pHEMA) hydrogels of different cross-linker and water contents was investigated in relation to the glass transition temperature (Tg) of the gels. After prolonged cooling at -15 degrees C a constant amount of 1.7 mol water per monomeric unit did not freeze, regardless of both the cross-linker and the water content of the gels. At this water content and temperature, pHEMA gels were below their Tg, and the water molecules were prevented from diffusing to the ice crystals formed in the gel. Therefore, the inability of part of the water in pHEMA gels to freeze is not a thermodynamic phenomenon but is caused by kinetic factors.
authors.affiliation: Center for Bio-Pharmaceutical Sciences, Division of Pharmaceutical Technology, The Netherlands.
authors.forename: W E
authors.initials: WE
authors.lastname: Roorda
authors.forename: J A
authors.initials: JA
authors.lastname: Bouwstra
authors.forename: M A
authors.initials: MA
authors.lastname: de Vries
authors.forename: H E
authors.initials: HE
authors.lastname: Junginger
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005615:Freezing; D005782:Gels; D011102:Polyhydroxyethyl Methacrylate / Q000032:analysis*; D011109:Polymethacrylic Acids / Q000032:analysis*; D013696:Temperature; D013816:Thermodynamics; D014867:Water
chemical_list: D005782:Gels; D011109:Polymethacrylic Acids; D014867:Water; D011102:Polyhydroxyethyl Methacrylate