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

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

Disruptions in the crystallinity of poly(lauryl methacrylate) due to adsorption on silica

“…When adsorbed, the polymer backbone of PLMA appears to be constrained as a result of hydrogen bonds between the carbonyl groups and the silica surface resulting in a reduction in the amount of crystallinity. A similar reduction in crystallinity occurred with adsorbed poly(vinyl acetate‐stat‐ethylene) on silica . The larger adsorbed amount samples (2.20 mg/m 2 and 3.26 mg/m 2 ) had much smaller fractions of bound carbonyls and as a result, the decrease in crystallinity was not as much as in the smallest adsorbed amount sample.…”

“…A similar reduction in crystallinity occurred with adsorbed poly(vinyl acetate-statethylene) on silica. 9 The larger adsorbed amount samples (2.20 mg/m 2 and 3.26 mg/m 2 ) had much smaller fractions of bound carbonyls and as a result, the decrease in crystallinity was not as much as in the smallest adsorbed amount sample.…”

“…In the case of adsorbed PLMA, the melting point remained constant indicating that the dimensions of the aggregates remained unchanged but the number of aggregates decreased. The adsorption of poly(ethylene‐stat‐vinyl acetate), on silica was also studied . The effect of adsorption on the crystallinity of the ethylene units was observed.…”

“…It has been suggested that PLMA contains a rigid amorphous region due to the confinement of the chains as a result of the presence of the nano‐domains . However, studies have shown that the adsorption of shorter chain methacrylate polymers onto silica instead results in a tightly bound layer which has a higher glass transition temperature than bulk polymer . The interest in PLMA is due to its high mobility ( T g is around −65 °C) and hydrophobicity, which allow its use as a viscosity modifier of motor oils .…”

“…2 However, studies have shown that the adsorption of shorter chain methacrylate polymers onto silica instead results in a tightly bound layer which has a higher glass transition temperature than bulk polymer. [8][9][10] The interest in PLMA is due to its high mobility 11 (T g is around 265 8C) and hydrophobicity, 12 which allow its use as a viscosity modifier of motor oils. 13 Nanocomposites with low T g polymers such as PLMA have also been used in pressure sensitive adhesives, 12 and thermally reversible light scattering films.…”