Μελέτη σχέσης δομής-ιδιοτήτων σε πολυμερικά δίκτυα διογκωμένα σε μη πολικούς διαλύτες

Abstract

his PhD thesis deals with the study of the plasticization effect on the polymer glasstransition in swollen poly(ethyl acrylate) polymer networks with non-polar solvents(1,4-dimethyl benzene, methyl benzene and ethyl benzene), the organization ofsolvent molecules within the polymer matrix and the respective molecular dynamicsThe study was focused on partially crystallized and amorphous polymer/solventmixtures with varying the cross-linking degree in polymer matrix and the type of nonpolarsolvent.The study of thermal transitions in these systems was carried out withDifferential Scanning Calorimetry (DSC). The study of the molecular dynamics wereperformed with two dielectric techniques: Thermally Stimulated DepolarizationCurrents (TSDC) and Dielectric Relaxation Spectroscopy (DRS).The experimental results have shown that the presence of solvent within thepolymer matrix induces the same degree of plasticization regardless of the nonpolarsolvent type and the polymer cross-linking degree. In partially crystallizedmixtures, the presence of non-crystalline phase is ascribed to kinetic reasons(entropic contribution) without invoking polymer-solvent interactions (enthalpiccontributions). Moreover, polymer segmental motions were found to be activated inpartially crystallized mixtures. Concerning the amorphous mixtures, the presence ofdynamic heterogeneity is originated by the high mobility contrast between twocomponents without meaning immiscibility. The high degree of swelling in polymernetworks inhibits the cooperativity of the polymer segmental dynamics close to theglass transition temperature, whereas theoretical models (Lodge and McLeish)adjusted to polymer mixtures describe very well the experimental results.