Effect of cross-linking on the molecular motions and nanodomains segregation in polymethacrylates containing aliphatic alcohol ether residues

The dielectric relaxation spectra of poly(2-ethoxyethyl methacrylate) in the frequency domain exhibits above T_g and at high frequencies a well-developed secondary Î3; relaxation. This process is followed in decreasing order of frequency for a relatively weak βrelaxation and an ostensible glass-rubber relaxation which at high temperatures and low frequencies is dominated by electrode-polymer interfacial processes. By slightly cross-linking the polymer using 2.5% (mol) of 2-ethoxyethyldimethacrylate as cross-linking agent, the %beta;relaxation disappears, the βrelaxation remaining. The activation energy of the β relaxation for the cross-linked and un-cross-linked polymers is ca. 30 kJ.mol^-1, about 10 kJ•mol^-1 below that of the %beta;relaxation. Cross-linking shifts the location of the glass-rubber relaxation nearly 10 °C to higher temperatures, without widening the distribution of relaxation times. The X-rays pattern of the cross-linked polymer presents two peaks at q = 5.6 nm ^-1 and 12.76 nm^-1, resembling the X-ray patterns of poly(n-alkyl methacrylate)s. The peaks in poly(n-alkyl methacrylate)s were attributed to the formation of nanodomains integrated by side chains flanked by the backbone. However, whereas this heterogeneity produces an α_PE peak in poly(n-alkyl methacrylate)s with n ≤2, this microheterogeneity gives rise to a Maxwell-Wagner-Sillars (MWS) relaxation in the cross-linked polymer located at lower frequencies than the glass rubber relaxation. Finally the interfacial-electrode conductive processes of the cross-linked and un-cross-linked polymeric systems are studied in the light of current theories.