화학공학소재연구정보센터
Macromolecules, Vol.45, No.8, 3571-3580, 2012
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 gamma relaxation. This process is followed in decreasing order of frequency for a relatively weak beta relaxation 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 gamma relaxation remaining. The activation energy of the gamma 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 degrees 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 alpha(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 crosslinked and un-cross-linked polymeric systems are studied in the light of current theories.