Browsing by Author "Diaz Calleja, Ricardo"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Relaxational behavior of poly(4-tetrahydropyranyl) methacrylate
    (WILEY, 2006) Sanchis, Maria J.; Dominguez Espinosa, Gustavo; Diaz Calleja, Ricardo; Alegria, Luz; Gargallo, Ligia; Radic, Deodato
    Complex permittivity of poly(4-tetrahydropyranyl methacrylate) (P4THPMA) was measured by dielectric spectroscopy. The spectra obtained show several relaxation processes labeled as delta, gamma, beta, and alpha in increasing order of temperature. These processes have been characterized and assigned to specific molecular motions. Comparison of the dielectric activity obtained for P4THPMAwith those reported for poly(1,3-dioxan-5-yl-methacrylate) (PDMA) and poly(cyclohexyl methacrylate) (PCHMA) was performed. In fact, these three polymers have similar chemical structures with aliphatic rings in the ester residue. However, significant differences between the dielectric behavior of these polymers have been observed. In addition, complementary molecular mechanic (MM) calculations have been carried out. The energy barriers obtained by these calculations lead to energy barriers which are in relatively good agreement with those derived from the dielectric measurement by means Arrhenius plots. (c) 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys44:3135-3147,2006.
  • Thumbnail Image
    Item
    Water sorption by poly(tetrahydrofurfuril methacrylate)'s
    (WILEY, 2008) Sanchis, Maria J.; Diaz Calleja, Ricardo; Garcia Bernabe, Abel; Alegria, Luz; Gargallo, Ligia; Radic, Deodato
    Polymers consisting of poly(heterocyclic methacrylate)s are considered as potential materials for clinical applications such as drug delivery and cartilage repair. Much of the success of these systems has been attributed to the complex nature of their water sorption properties. Dielectric permittivity is very sensitive to water sorption. Dielectric relaxation spectroscopy studies have been carried out on two heterocyclic poly(methacrylate)s: poly(tetrahydrofurfuryl methacrylate) (PTHFMA) and poly (3-methyl tetrahydrofurfuryl methacrylate) (P3MTHFMA). The isochrones representing the dielectric losses show in both cases high conductivity at low frequencies and high temperatures. In PTHFMA two conductive processes are observed, which can be associated to the existence of two types of water sorption. These effects have been analyzed and were removed from the dielectric spectra by using classical empirical equations. Both polymers show ostensible alpha-relaxation centered in the vicinity of 350 K at 10(0) Hz. This relaxation was analyzed by means of the empirical Havriliak-Negami equation. Reminiscent beta-relaxation could also exist. Both polymers present well defined gamma and delta subglass absorptions at approximately 120 K, 160 K for PTHFMA and 125 K, 163 K for P3MTHFMA, at 10(0) Hz, associated to local intramolecular relaxations in side groups. These relaxations were analyzed using semiempirical symmetric model. (C) 2007 Wiley Periodicals, Inc.