title: The effect of cross-linking on the molecular dynamics of the segmental and β Johari-Goldstein processes in polyvinylpyrrolidone-based copolymers.
abstract: The effect of the cross-link density on the molecular dynamics of copolymers composed of vinylpyrrolidone (VP) and butyl acrylate (BA) was studied using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). A single glass transition was detected by DSC measurements. The dielectric spectra exhibit conductive processes and three dipolar relaxations labeled as α, β and γ in the decreasing order of temperatures. The cross-linker content affects both α and β processes, but the fastest γ process is relatively unaffected. An increase of cross-linking produces a typical effect on the α process dynamics: (i) the glass transition temperature is increased, (ii) the dispersion is broadened, (iii) its strength is decreased and (iv) the relaxation times are increased. However, the β process, which possesses typical features of a pure Johari-Goldstein relaxation, unexpectedly loses the intermolecular character for the highest cross-linker content.
authors.affiliation: Instituto Tecnología Eléctrica, Departamento de Termodinámica Aplicada, Universitat Politècnica de València, Camí de Vera s/n, 46022, Valencia, Spain. jsanchis@ter.upv.es.
authors.forename: Belén
authors.initials: B
authors.lastname: Redondo-Foj
authors.forename: María Jesús
authors.initials: MJ
authors.lastname: Sanchis
authors.forename: Pilar
authors.initials: P
authors.lastname: Ortiz-Serna
authors.forename: Marta
authors.initials: M
authors.lastname: Carsí
authors.forename: José Miguel
authors.initials: JM
authors.lastname: García
authors.forename: Félix Clemente
authors.initials: FC
authors.lastname: García
mesh_terms: D000179:Acrylates / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D003432:Cross-Linking Reagents / Q000737:chemistry*; D058266:Dielectric Spectroscopy; D055595:Mechanical Phenomena; D008689:Methacrylates / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D011108:Polymers / Q000737:chemistry*; D011205:Povidone / Q000737:chemistry*; D013696:Temperature
chemical_list: D000179:Acrylates; D003432:Cross-Linking Reagents; D008689:Methacrylates; D011108:Polymers; C032490:n-butyl acrylate; C004919:ethylene dimethacrylate; D011205:Povidone