P. Sakellariou

Lamellar structure in a thin polymer blend film

Abstract We have fully characterized the three-dimensional morphology of thin films of mixtures of polystyrene and polybutadiene cast from a toluene solution, using nuclear reaction analysis, neutron reflectometry and transmission electron microscopy. Polystyrene-rich phases wet both the air and substrate interfaces and are separated by a polybutadiene-rich phase; these layers are very well defined and the interfaces between them are sharp (down to A ). Within the polybutadiene-rich central layer, lateral phase separation is also evident, with polystyrene-rich domains of oblate spheroidal shape. Under certain circumstances thin polystyrene-rich layers exist within the polybutadiene-rich phase. We discuss possible mechanisms for this unusual morphology in terms of surface effects on the mechanism of phase separation in the ternary polymer-solvent system from which the films are cast.

Phase separation and polymer interactions in aqueous poly(vinyl alcohol)/hydroxypropyl methylcellulose blends

This paper discusses the compatibility of aqueous hydroxypropyl methylcellulose (HPMC)/poly(vinyl alcohol) (PVA) blended systems. Dynamic mechanical analysis and differential scanning calorimetry have provided clear evidence of two phases. Each phase precluded almost completely the other component. The HPMC-rich phase was amorphous with a constant Tg while the PVA-rich phase showed a limited level of crystallinity and a constant Tg for the amorphous part. Fourier-transform infra-red studies indicated hydrogen-bonding interactions involving the carbonyl and hydroxyl groups of like molecules but no detectable interactions between HPMC and PVA. A new hydrogen-bonding environment of the hydroxyls was observed in the blended system but was not capable of inducing any compatibility. The gross incompatibility was successfully predicted by the total solubility parameters of the two polymers and attributed to significant differences in the polar and hydrogen-bonding contributions. Surface energy analysis corroborated the inability of the two chains to participate in acid-base interactions between unlike molecules due to significant discrepancies in their Lewis acid-base characteristics. Finally, determination of the free energy of polymer-polymer interaction in water allowed approximate calculation of the Flory-Huggins parameters of aqueous PVA and HPMC systems.

Hydrogen bonding. Part 25. The solvation properties of methylene iodide

Ostwald solubility coefficients, L, have been determined for 37 gases and vapours in methylene iodide at 298 K, and have been correlated through equation (i), where the solute explanatory log L=–0.74 + 0.32R2+ 1.34π2H+ 0.83α2H+ 1.19β2H+ 0.87 log L16(i) variables are R2 an excess molar refraction, π2H the solute dipolarity/polarisability, α2H and β2H the solute hydrogen-bond acidity and basicity, and log L16 where L16 is the solute Ostwald solubility coefficient on hexadecane at 298 K. Similar equations have been constructed for solvation of solutes in tetrachloromethane, trichloromethane and 1,2-dichloroethane using literature data. It is shown that polarisability effects favour solvation in methylene iodide, through the R2 term, but that such effects enhance the solubility of polarisable solutes only moderately: thus the R2 term contributes 0.4 log units more in methylene iodide than in trichloromethane for the solute benzene. Examination of ΔG°, ΔH° and ΔS° for solvation of gaseous solutes suggests also that polarisability effects in methylene iodide are not very much larger than in the other halogenated solvents.

Effect of polymer compatibility on surface enrichment in polymer blends

Abstract The surface composition of blends of poly(ethylene oxide) (PEO) with polystyrene (PS), poly(methyl methacrylate) (PMMA) and random copolymers of styrene and methyl methacrylate (MMAS) has been studied as a function of blend and copolymer compositions. In the case of homopolymer blends, only the incompatible blend PEO/PS showed significant surface enrichment in PS following annealing at temperatures above the T g of the two constituents and the T m of PEO. The compatible system PEO/PMMA presented a mixed surface. Surface enrichment in the MMAS copolymers was observed in all PEO/MMAS blends with styrene contents in excess of 2% w/w. This has been attributed to the incompatibility between the PEO and the MMAS copolymers as shown by the ternary phase diagram PEO/MMAS/CHCl 3 and the melting-point depression of the PEO-rich phases with varying copolymer composition and concentration. Angle-dependent X-ray photoelectron spectroscopy provided an indication of the depth-concentration profile of the blend. The results of these measurements demonstrate that increased styrene content in the MMAS copolymer produces deeper concentration profiles, which reached down to 69 A from the surface. Mean-field calculations of the depth-concentration profile for a selected system gave very good agreement with the experimental data.

An analysis of polymer-probe interactions in some hydrocarbon polymers using a new solvation equation

The new solvation equation: log L= c + rR2 + sπH22 + aαH2 + bβH2 + l log L16 has been applied to the solubility of 43 gaseous probes on each of nine hydrocarbon polymers using the data of Munk et al.. In this equation, L is the gas-liquid partition coefficient of a series of probes on a given polymer, and the explanatory variables are solute properties as follows: R2 is an excess molar refraction, πH2 is the probe dipolarity-polarizability, αH2 and βH2 are the probe hydrogen-bond acidity and basicity, and L16 is the gas-liquid partition coefficient of the probe on hexadecane at 25°C. Each of the nine equations, one for each polymer, had correlation coefficients of around 0.999 and standard derivations of around 0.025 log units. The solubility of the gaseous probes, as log L values, as well as the polymer-probe interaction parameter χ calculated by Munk, have been analysed in terms of particular polymer-probe interactions.

Plasticization of aqueous poly(vinyl alcohol) and hydroxypropyl methylcellulose with polyethylene glycols and glycerol

Abstract The plasticization of aqueous hydroxypropyl methylcellulose (HPMC) and poly(vinyl alcohol) (PVA) with poly(ethylene glycols) (PEGs) with various molecular weights and with glycerol has been investigated. The plasticizing efficiency in the case of HPMC was: PEG200 > PEG400 > GLYCEROL > PEG6000 and for PVA: GLYCEROL > PEG200 > PEG400 > PEG6000. The plasticizer efficiency rating was explained with the partial solubility parameters of the polymers and the plasticizers in terms of the propensity of each polymer-plasticizer pair to set up polar and hydrogen-bonding interactions. Phase separation of the plasticizers occurred above a critical concentration which, in the case of PEGs, was inversely proportional to molecular weight. Phase separation of the plasticizer was shown to be responsible for deterioration in the plasticizing efficiency.

Comparison of uncorrected retention data on a capillary and a packed hexadecane column with corrected retention data on a packed squalane column

Abstract Retention data obtained previously at 25°C on a hexadecane capillary column by Zhang et al. and a packed hexadecane column by Abraham et al., both uncorrected for any effects due to interfacial adsorption, were compared with retention data obtained by Poole et al. on a packed squalane column at 120°C, with the latter fully corrected for such effects. It is shown that for most solutes, the capillary and packed column data are equally compatible with the squalene corrected data, but for the solutes dimethyl sulfoxide, dimethylformamide and dimethylacetamide the packed column data are in much better accord with the corrected data than are the capillary column data. It is further shown that both sets of results at 25°C for carboxylic acids are in error, owing to dimerization. Retention volumes on Chromosorb G AW DMCS are reported at 25 and at 93°C. It is shown that at 25°C, there could be some contribution to solute retention from adsorption on the support, but that this is almost impossible at 93°C.

Solubility characteristics of poly(ethylene oxide): Effect of molecular weight, end groups and temperature

AbstractThe general solvation equation

Thermal properties of poly(ethylene oxide)-poly(methyl methacrylate) blends and copolymers complexed with sodium thiocyanate

{\text{Log }}L = c + r \cdot R_2 + s \cdot \pi _2^{\text{H}} + a \cdot \alpha _2^{\text{H}} + b \cdot \beta _2^{\text{H}} + l \cdot \log {\text{ }}L^{16}