Bound carbonyls in PMMA adsorbed on silica using transmission FTIR

Macromolecular Symposia

2013

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Summary The behavior of an amorphous polymer, poly(methyl methacrylate) (PMMA), adsorbed on silica was studied using temperature‐modulated differential scanning calorimetry (TMDSC). A two‐component model, based on loosely‐bound polymer with a glass transition temperature (Tg) (similar to that of the bulk polymer) and a tightly‐bound polymer (with a Tg higher than that of the loosely‐bound polymer) was used to interpret the thermograms. Increased sensitivity allowed the two transitions in the thermograms to be quantified much more accurately than in previous work. Linear regression analysis of the ratio of the area under two transitions with composition yielded the amount of tightly bound polymer, m″B = 1.21 +/− 0.21 mg PMMA/m2silica. Two methods of analyzing the thermograms, fitting with a Gaussian‐Lorentzian (GL) cross distribution function and perpendicular drop (PD) method, yielded similar results for the amount of tightly‐bound polymer on the surfaces with the GL method having a statistically better fit to the model. The ratio of heat capacity increments of loosely bound and tightly bound polymer, ΔCpA/ΔCpB, around the glass transition, indicated the relative mobility of the two components. It was found that the ΔCpA was aboutthree times as large as that of ΔCpB suggesting that the tightly bound polymer had a much smaller change in mobility through glass transition region.

Section: Discussionmentioning

confidence: 93%

“…This ratio can be expressed as a function of the experimental observable, r , as:

f_{normalB} = {m^{'}}_{pB} / {m^{'}}_{normalp} = m_{pB} / m_{normalp} = {m^{″}}_{pB} / {m^{″}}_{normalp} = 1 / (1 + r Δ C_{pB} / Δ C_{pA})

Section: Bound‐segment Modelmentioning

confidence: 99%

Thermal Properties of PMMA on Silica Using Temperature‐Modulated Differential Scanning Calorimetry

Khatiwada

Hetayothin

Macromolecular Symposia

2013

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“…The peak areas of the bound and free carbonyl resonances of adsorbed PEVAc and PVAc obtained using OriginPro 8.6 software were used to fit the data to the model developed by Kulkeratiyut et al in 2006 . Based on this model the relative intensities would be expected to fit the following equation:

M_{normalt} = M_{normalb} + (A_{normalf} / A_{normalb}) X M_{normalb}

where M t is the total adsorbed amount of the polymer, M b is the mass of the polymer segments which are bound to the silica surface, A f and A b are the absorbances corresponding to the free carbonyl resonances and bound carbonyl resonances, respectively, and X is the ratio of the molar absorption coefficients of the bound and free carbonyl resonances.…”

Section: Resultsmentioning

confidence: 99%

“…From the results in Table , insight can be gained on the structure of the adsorbed copolymer. M b for a particular polymer represents the mass of the polymer segments of the bound carbonyls . The value of M b is a hypothetical mass of the polymer with carbonyls covering the silica surface.…”

Section: Discussionmentioning

confidence: 99%

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

Maddumaarachchi

J Polym Sci B Polym Phys

2014

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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

“…From these, the bound fraction of carbonyl groups, p , was calculated from eq

p = \frac{(|, A_{normalb} / X)}{([]|, A_{normalb} / X + A_{normalf})}

where X is molar extinction coefficient ratio of bound to free carbonyls, A f is the intensity of the free carbonyl band, and A b is that of the bound carbonyl band . This estimation requires knowledge of the adsorption coefficients of the bound and free carbonyl or their ratio denoted as X in the equation above . The value of X for PLMA was determined to be 11.9 ± 2.0 using FTIR‐ATR (see Supporting Information) and had been previously estimated as X = 11.1 ± 2.9 using transmission mode FTIR .…”

Section: Resultsmentioning

confidence: 99%

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

Arua

J Polym Sci B Polym Phys

2017

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The effects of adsorption of poly(lauryl methacrylate) (PLMA), a side-chain crystalline polymer, on silica were investigated. Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC) measurements were made on both bulk and adsorbed PLMA. The reversible heat flow rates were observed as a function of temperature and the degree of crystallinity of the samples determined based on the broad melting transitions of the side chains in the surface samples. It was found that adsorption caused a disruption of the side-chain crystallinity primarily in the tightly bound layer of the polymer, but did not significantly affect its glass transition temperature. A change in the packing of the hydrophobic side chains, as a result of adsorption, was also observed for the tightly adsorbed polymer. These results indicated that PLMA side chains in proximity to the silica surface have different properties from those in bulk PLMA.