Thermal analysis and FT-IR studies of adsorbed poly(ethylene-stat-vinyl acetate) on silica

• Published in: Journal of polymer science. Part B, Polymer physics Polymer physics, 2014-05, Vol.52 (10), p.727-736
• Main Authors: Maddumaarachchi, Madhubhashini, Blum, Frank D.
• Format: Article
• Language: English
• Subjects: Acetates; adsorption; Applied sciences; bound fraction; Carbonyls; copolymer; Copolymers; Ethylene; Exact sciences and technology; FTIR; Glass transition; Organic polymers; Physicochemistry of polymers; Polyethylenes; Properties and characterization; silica; Silicon dioxide; Surface properties; TMDSC; Vinyl acetate
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.23476

ABSTRACT Adsorbed poly(ethylene‐stat‐vinyl acetate) (PEVAc) on fumed silica was studied using temperature‐modulated differential scanning calorimetry (TMDSC) and FT‐IR spectroscopy. The properties of the copolymers were compared with poly(vinyl acetate) (PVAc) and low density polyethylene (LDPE) as references. TMDSC analysis of the copolymer‐silica samples in the glass transition region was complicated for the copolymers because of the ethylene crystallinity. Nevertheless, examination of the glass transition region for small adsorbed amounts of these copolymers indicated the presence of tightly‐ and loosely‐bound polymer segments, similar to other polymers which have an attraction to silica. Compared with bulk polymers with the same composition, the tightly‐bound polymers showed an increased glass transition temperature (Tg) and a loosely‐bound fraction with a lower Tg than bulk. FT‐IR spectra of the surface copolymers indicated that the fraction of bound carbonyls (p) increased as the fraction of vinyl acetate in the copolymers decreased, consistent with the notion that the carbonyls from vinyl acetate preferentially find their way to the silica surface. Spectra from samples with different adsorbed amounts of polymer were used to obtain the amount of bound polymer (Mb) and the ratio of molar absorption coefficients of bound carbonyls to free carbonyls (X). The copolymers had very large p values (up to 0.8) at small adsorbed amounts and dependent on the composition of the polymer. However, an analysis of the bound fractions, based on only the vinyl acetate groups, superimposed the data, suggesting that the ethylene units simply dilute the vinyl acetate groups in the surface polymer. The sample with the smallest fraction of vinyl acetate did not show this behavior and may be considered to be “carbonyl poor.” © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 727–736 The structure and thermal behavior of adsorbed poly(ethylene‐stat‐vinyl acetate) on fumed silica was studied using temperature‐modulated differential scanning calorimetry and FT‐IR spectroscopy. Carbonyls from vinyl acetate preferentially found their way to the silica surface over the ethylene segments. When based on the vinyl acetate content alone, the copolymers showed consistent bound fractions regardless of copolymer composition, except for the one with the smallest amount of vinyl acetate, which could be considered to be “carbonyl poor.”