Effect of Cross-Linking on the Molecular Motions and Nanodomains Segregation in Polymethacrylates Containing Aliphatic Alcohol Ether Residues

Abstract

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 γ relaxation. This process is followed in decreasing order of frequency for a relatively weak β 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 β relaxation disappears, the γ relaxation remaining. The activation energy of the γ 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 β 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 αPE 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.

Relaxational study of poly(vinylpyrrolidone-co-butyl acrylate) membrane by dielectric and dynamic mechanical spectroscopy

“…Moreover, the characterization of the α relaxation, directly related to the glass transition, is sometimes difficult to carry out for wet membranes. This is related to the high intensity of the water conductive effects, which masks or does not allow a clear definition of the α relaxation [25,[32][33].…”

Influence of the Water Content on the Diffusion Coefficients of Li+ and Water across Naphthalenic Based Copolyimide Cation-Exchange Membranes

“…Polar polymers with nanodomains formed by segregation of polar side groups from the nonpolar backbone 5,6 present just above ω c a distributed Maxwell− Wagner−Sillars (MWS) relaxation produced by relatively long distance charges transport. In increasing order of frequency, the glass−rubber relaxation arising from segmental motions of the polymer chains as well as secondary relaxation processes produced by local motions affect the ac conductivity of polymeric systems.…”

A contribution to the study of the molecular mobility in polymeric materials by Thermal and Dielectric Analysis

“…This behavior has been observed in some systems where the formation of nanodomains, integrated by the side chains flanked by the backbone, is produced (Carsí, et al, 2012;Carsí, et al, 2013). This effect can be understood due to a decrease in the free volume.…”

“…The dynamic mechanical and dielectric properties are intrinsically correlated and they are associated with a structural polymer feature (McCrum, et al, 1991;Sanchis, et al, 1999;Carsí, et al, 2012;Carsí, et al, 2013;Deutsch, et al, 1954). The dynamic relaxation properties of cross-linked polymer networks are highly sensitive to network composition and polymer chain architecture.…”

“…The effect of cross-linking in the segmental transition, also called α relaxation, usually broadens the dispersion and makes its relaxation time more sensitive to temperature, that is, the material becomes more fragile. On the other hand, it is found that the cross-linking may produce different effects in the sub-glass transitions, which may be related to their molecular origin (Casalini, et al, 2010;Carsí, et al, 2012;Carsí, et al, 2013;Kalakkunnath, et al, 2007;Sabater i Serra, et al, 2009) In the previous chapter, the effect of copolymer composition in a family of VP and BA copolymers with a different proportions of monomers and a fixed cross-linker molar ratio of 1% was studied using different characterization techniques. The dielectric spectra showed three relaxations, γ, β and α, followed by conductive processes.…”