Structure and properties of ethylene—methacrylic acid copolymers and their sodium salts: Dielectric and proton magnetic relaxation studies

Abstract

AbstractDielectric and proton magnetic relaxation data have been obtained for an ethylene‐methacrylic acid copolymer (containing about 4 mole% methacrylic acid units) and its 53% ionised sodium salt. The degrees of crystallinity and percentage ionisation of the samples investigated were estimated by infra‐red methods.The dielectric results were obtained principally in the frequency range 100 Hz to 10 kHz and at temperatures ranging from 80° to – 120°. A few results are also reported at frequencies down to 0·1 Hz and up to 100 MHz. For the acid copolymer, two dielectric loss regions are observed and these are correlated with the reported mechanical β′‐ and γa‐processes respectively. The partly ionised copolymer exhibits three dielectric relaxation regions which correlate with the mechanical α‐, β‐ and γa‐relaxations respectively. In addition, a dielectric peak appears at about —40° in the presence of absorbed water, a result similar to that found in the polyamides.The proton magnetic relaxation results were obtained by pulse methods which yielded the spin‐lattice relaxation times T1 (at 30 MHz) and T1p (at kilohertz frequencies) as a function of temperature from −180° to 100°. Two components were generally observed for T1p. For the acid copolymer the β′‐ and γ‐processes have been observed from these results, as well as a lower‐temperature (δ) process which has not been detected by the mechanical or dielectric methods. For the sodium salt the γ‐ and δ‐processes are also found, in addition to a high‐temperature process in the region of the merged α‐ and β‐processes.The present data are consistent with previous assignments for the β′‐, α‐, β‐ and γ‐processes. The ‘water’ relaxation appears to involve some rotation of water molecules, or of ionic segments to which water molecules are attached, in the proposed ionic domains. The δ‐process is ascribed to the rotations of methyl groups present in the methacrylic acid units.