Relationship between microstructure and phaseand relaxation transitions in ethylene-(vinyl acetate) copolymers prepared by emulsion copolymerization

• Published in: Polymer (Guilford) Vol. 39; no. 12; pp. 2583 - 2588
• Main Authors: Gospodinova, Natalia, Zlatkov, Todor, Terlemezyan, Levon
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1998
• Subjects: ethylene-(vinyl acetate) copolymers; phase transitions; relaxation; ethylene-(vinyl acetate) copolymers; phase transitions; relaxation
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(97)00558-2

The relaxation and phase transitions in ethylene-(vinyl acetate) (EVA) copolymers prepared by emulsioncopolymerization were studied. Substantial deviations of the basic characteristics of the transitions (glass transition temperature,
T
g, melting temperature,
T
m, and degree of crystallinity,
W
c) from those known for commercial products and, to a greater extent, for low-conversion copolymers synthesized in solution were found. These deviations were explained by the effect of the microstructure and particularly by the configurational heterogeneity of the copolymer chains. Thus, different fractions of EVA copolymer fractionated according to the chemical composition revealed values of
T
g,
T
m and
W
c suggesting the existence of two parts in the copolymer chains. The comonomer units in one part show a tendency to alternate while the ethylene units in the other part show an enhanced tendency to form blocks. A similar model of the microstructure of the copolymers studied was presented in our previous communication where the distribution of the comonomer units along the polymer chains was studied by means of
13C n.m.r. spectroscopy. It is now established that the overall chemical composition of the copolymer and its fractions studied, calculated based on the experimental values of
T
g,
T
m and
W
c, fitted fairly well with the composition found experimentally, thus confirming the correctness of the model of the microstructure proposed.