The melting temperature of a thermally reversible gel. II. ethylene–vinyl acetate copolymer–organic solvent gels

Abstract

Thermally reversible gels were formed from dilute solutions of ethylene–vinyl acetate copolymer (EVA) in dioxane, ethyl acetate, methyl ethyl ketone, and methyl isobutyl ketone. The power of solvents to form the gels were almost identical. The X-ray diffraction pattern of the EVA gels revealed that the gels were crystalline and that the crystallites, which serve as “cross-links”, consisted of blocks of ethylene units in the copolymer. EVA copolymers, having ethylene mole fractions (XA) from 0.64 to 0.84, and ethyl acetate systems were studied in detail. The linear relationship between the reciprocal absolute melting temperature (Tmg) and the logarithm of v2x was found for each EVA, where v2 is the volume fraction of polymer and x the degree of polymerization. The results were analysed using the theoretical expression given in the previous paper. The analysis leads to the conclusion that the ethylene sequence length in the crystallites, i.e., the block length of ethylene unit in the copolymer, is 10 irrespective of XA. It was also shown that the conclusion is in accordance with the block length estimated by Wu from the 220-MHz NMR spectra of EVA-copolymer solutions. © 1973, The Society of Polymer Science, Japan. All rights reserved.