J. S. Chiou

A completely miscible ternary blend: poly(methyl methacrylate)-poly(epichlorohydrin)-poly(ethylene oxide)

Abstract The polymer pair poly(epichlorohydrin) (PECH) and poly(ethylene oxide) (PEO) is shown to form completely miscible blends based on the observation of a single glass transition temperature (Tg) by differential scanning calorimetry and lower critical solution temperature (LCST) behaviour. Since poly(methyl methacrylate) (PMMA) is known from earlier work to form miscible binary blends with PECH and with PEO, then a ternary system (PMMA-PECH-PEO) has been identified for which all three binary pairs are miscible. Examination of ternary blends for Tg and LCST behaviour revealed that complete miscibility exists over the entire ternary composition diagram. Heats of mixing for binary mixtures of liquids whose molecular structures are analogues of the polymers are reported in order to understand better the nature of the interactions operative in each of the binary blends. It is seen that oligomeric analogues for poly(ethylene oxide) give misleading results when they have hydroxyl end groups.

Gas sorption and permeation in poly(ethyl methacrylate)

Abstract Gas sorption isotherms for N2, Ar, CH4, and CO2 have been measured at various temperatures for poly(ethyl methacrylate) (PEMA) below its Tg. For the three low solubility gases, N2, Ar and CH4, the sorption isotherms are concave as predicted for glassy polymers but the amount of sorption in PEMA is much lower than that in high Tg polymers. For the higher solubility gas CO2, however, the amount of sorption is the same as that in high Tg polymers. The CO2 isotherms changed from concave at low pressures to a straight line at high pressures, which can be extrapolated to the origin of the coordinates, indicating the PEMA is plasticized by CO2 from the glassy to the rubbery state. The sorption parameters for CO2 are derived from a modified dual mode sorption equation which considers the plasticizing effect. New findings about these parameters and the derived enthalpy change on sorption are reported. Gas permeability coefficients for PEMA to He, H2, O2, Ar, N2, and CH4 measured at 35°C are observed to be independent of pressure. On the other hand, the CO2 permeability coefficients increase with pressure. Appropriate models are used to describe this transport behavior. Evidence from gas sorption and DSC thermograms show that PEMA can sub-Tg anneal under CO2 plasticization. However, when the Tg is depressed by plasticization below the observation temperature, the annealing effect is erased. This leads to complex behavior as described.

Effects of CO2 exposure on gas transport properties of glassy polymers

Abstract The effects of CO2 driving pressure and CO2 exposure history on transport properties for two polycarbonates and two acrylic polymers are described. For the polycarbonates, the CO2 permeability decreases with increased driving pressure while exposure to CO2 causes in subsequent measurements a decrease in permeability and an increase in the diffusion time lag. For the acrylics, each response is exactly the opposite. The effects may be important for membrane separation processes involving CO2 at high pressures.

Miscibility of SAN with polyacrylates and polymethacrylates

Abstract Styrene-acrylonitrile copolymers, SAN, are known to be miscible with poly(methyl methacrylate). Based on the presence of a single composition dependent glass transition and lower critical solution temperature behaviour, it is shown that SAN is also miscible with poly(ethyl methacrylate). However, the SAN does not appear to be miscible with other polymethacrylates or polyacrylates.