Sorption and diffusion of water vapour in hydrogen-bonded polymer blends

ABSTRACT:Successive desorption experiments of water vapor in poly(methyl methacrylate) (PMMA) were performed at temperatures from 31.0 to 45.0°C. The solubility of water in PMMA was found to be independent of temperature in agreement with literature findings. But the results for diffusion showed stronger dependence on water concentration than those in literature. The diffusion coefficients of water in PMMA became almost independent of temperature at high water concentrations. However, at lower water concentrations, the temperature effect on diffusion was more pronounced. The observed weak temperature dependence of diffusivity at high concentrations is likely due to a high degree of clustering of water molecules found in the PMMA we prepared. Two modified polystyrenes containing 5 and 15 mol %, respectively, 4-hydroxystyrene as comonomer units were blended with PMMA to form hydrogen-bonded polymer blends. Successive desorption experiments of water vapor in the hydrogenbonded polymer blends were carried out at 31.0°C. The solubility of water in both blends was found to increase with increasing composition of PMMA. The diffusion coefficients for PMMA and its blends increased with increasing concentration of water first, reached a maximum, then decreased with water concentration. When the desorption results were plotted with the previous study of absorption, hysteresis phenomenon of sorption existed in all blend compositions for our experimental time span.

Section: Composition Dependence Of Diffusivity At C Equal To 0125contrasting

confidence: 80%

Section: Hysteresis Phenomenonmentioning

confidence: 90%

See 1 more Smart Citation

Desorption of water vapor in hydrogen-bonded polymer blends

Hsu

Myerson²,

Kwei³

1998

“…In the latter blends, the T g values are higher by 1-4°C than the weight average predictions. 18 Jong also found that two compositions (50 and 70% iPMMA) of the iPMMA/MPS-5 blends showed three transitions, indicative of multiple phases present in the blend. From Jong's results, the following research was prompted.…”

Section: Introductionmentioning

confidence: 93%

“…When the spectra of the three PMMA/PHS (75/25) blends were plotted together in Figure 13, there was be minimal. 9,18 From FTIR results of both carbonyl and hydroxyl absorptions, the following comments can be drawn. iPMMA and aPMMA have a higher degree of hydrogen bonding with PHS than sPMMA.…”

mentioning

confidence: 97%

Polymer blends of stereoregular poly(methyl methacrylate) and poly(styrene-co-p-hydroxystyrene)

Hsu

Yeh

1999

Isotactic, atactic, and syndiotactic poly(methyl methacrylates) (PMMAs) (designated as iPMMA, aPMMA, and sPMMA) were mixed with poly(styrene-co-phydroxystyrene) (abbreviated as PHS) containing 15 mol % of hydroxystyrene separately in 2-butanone to make three polymer blend systems. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to study the miscibility of these blends. The three polymer blends were found to be miscible, because all the prepared films were transparent and there was a single glass transition temperature (T g ) for each composition of the polymers. T g elevation (above the additivity rule) is observed in all the three PMMA/PHS blends mainly because of hydrogen bonding. If less effective hydrogen bonding based on the FTIR evidence is assumed to infer less exothermic mixing, sPMMA may not be miscible with PHS over a broader range of conditions as iPMMA and aPMMA.

Molecular mobility and hydration properties of segmented polyurethanes with varying structure of soft- and hard-chain segments

Kanapitsas

Pissis

Ribelles

et al. 1999

The molecular mobility and hydration properties of model segmented polyurethanes from either poly(propylene glycol) (PPG) or poly(butylene adipate) (PBAD), both of molecular weight 2000 (soft segments), and three different diisocyanates (all‐trans 4,4′‐dicyclohexylmethane diisocyanate, 100% t,t HMDI; HMDI with 20% of trans isomers, 20% t,t HMDI; and 4,4′‐diphenylmethane diisocyanate, MDI) (hard segments) were investigated using differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) measurements, ac dielectric relaxation spectroscopy (ac DRS), equilibrium water‐sorption isotherms (ESI), and dynamic water‐sorption isotherms (DSI). No effects of the structure and of the amount of the soft segments on the overall degree of microphase separation (DMS) into microphases rich in soft and hard segments, respectively, were observed. On the contrary, DMS depends on the composition of the diisocyanates used and systematically increases in the order MDI, 20% t,t HMDI, 100% t,t HMDI as indicated by DSC, TSDC, and ac DRS. The PPG‐based polyurethanes are characterized by larger values of water content at saturation, h, and smaller values of the diffusion coefficient of water, D. h increases with temperature, indicating that the sorption process is endothermic. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1209–1221, 1999