Evaluation of interactions in blends of ethylene-vinyl acetate copolymers with poly(vinyl chloride) using model compounds

• Published in: Macromolecules 1989-05, Vol.22 (3), p.1289-1300
• Main Authors: Cruz-Ramos, C. A, Paul, D. R
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical modifications; Chemical reactions and properties; Exact sciences and technology; Organic polymers; Physicochemistry of polymers
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma00193a049

The interactions in blends of ethylene--vinyl acetate copolymers (EVA) with poly(vinyl chloride), PVC, have been examined by using low molecular weight analogues of the polymers. To simulate the different ethylene/vinyl acetate ratios in the copolymers, premixes of heptane with ethyl acetate or with 1,3-butanediol diacetate were used, as were several alkyl acetates; 2,4-dichloropentane, 2,4-DCP, was chosen to model PVC. The heats of mixing of the EVA analogues with 2,4-DCP were found to be exothermic where their polymeric counterparts show miscibility. Hence, the miscibility window reported for the EVA--PVC system at one-to-one ratios of the two polymers can be approximately traced by these calorimetric results. The heats of mixing determined have a complex nature and, in some cases, endothermic and exothermic behavior was found when mixing a single EVA analogue with the PVC model in different proportions. The weak endothermic portion in those cases was invariably located at high contents of 2,4-DCP; this agrees, at least qualitatively, with a trend toward immiscibility for blends in the PVC-rich region. Application of a binary interaction model to the calorimetric results allowed only a qualitative prediction of the miscibility window for EVA--PVC blends, owing almost certainly to the nonparabolic behavior of the heats of mixing. Fourier transform infrared spectroscopy was used to follow the features of the carbonyl group when the analogues were placed in different molecular environments. This suggests three possible mechanisms govern phase behavior in the polymer blends: dispersive forces, the disruption of carbonyl dipole--dipole interactions in EVA, and a specific interaction between the C=O and CHCl groups, which has been identified in the polymers. Only the latter mechanism contributes exothermically to the enthalpy of mixing. Apparently, the specific interaction contribution is able to counteract the other two components only within the limits of the miscibility window for the EVA--PVC system. 45 ref.--AA