Melt intercalation/exfoliation of polystyrene-sodium-montmorillonite nanocomposites using sulfonated polystyrene ionomer compatibilizers

Quaternary ammonium salts of sulfonated polystyrene (SPS) were used as compatibilizers for melt intercalation of PS and pristine Na-montmorillonite. Tetra-octyl ammonium SPS and tetra-decyl ammonium SPS ionomeric compatibilizers produced significant exfoliation and a homogeneous dispersion of the polymer-clay nanocomposites. Wide angle X-ray diffraction and transmission electron microscopy were primarily used to characterize the morphology of the nanocomposites. Image analysis was used to measure the percentage exfoliation. Exfoliation increased with the increasing length of the alkyl chain of the ammonium counter-ion of the SPS ionomer. The nanocomposites containing ionomers exhibited higher storage moduli compared to nanocomposites without the compatibilizer.     

Side-chain functionalized liquid crystalline polymers and blends, 10: phase behavior and structure of side-chain liquid crystalline ionomers containing ions of d-metals

Novel side-chain liquid crystalline (LC) ionomers containing d-metals Co(II) and Ni(II) were synthesized and characterized. Both families of the ionomers are characterized by the same influence of charged group content in polymer on their phase behavior. The incorporation of 2-3 mol% of metal ions in the nematic polymer matrix leads to the induction of SmA phase and rise in the clearing point. The peculiarity of their phase behavior in comparison with the earlier investigated LC ionomers with alkaline or alkali-earth metals is the full destruction of the mesophase at the concentration of d-metal higher than 12 mol%. This phenomenon was associated with the well-known ability of the transition metal ions to form various complexes that, in the case of LC ionomers, can negatively influence the ordering of the side mesogenic groups. The proposed structure of the LC ionomers is discussed in comparison with the metallomesogenic polymer systems.     

The effect of relative humidity on the gas permeability and swelling in PFSI membranes

The permeation of helium, oxygen and nitrogen in perfluorosulphonic acid ionomeric (PFSI) membranes with short and long side chains, namely Aquivion^® and Nafion^® 117, was studied in the relative humidity range between 0 and 90%, and at temperatures between 35 °C and 65 °C. The presence of humidity enhances, up to a factor of 100, the gas permeability in the membranes, due to the permeation of gas molecules in the hydrophilic domains: the enhancement is rather pronounced for O₂ and N₂, and less marked for He permeability. The relative permeability increase, P_gas/P_gas,0, shows a complex dependence on the relative humidity, as the water content in the membrane is itself a non linear function of this parameter. The water volume fraction in the membrane at each activity was accurately estimated from measurements of vapor-induced swelling, which indicate that the partial molar volume of water is smaller than its pure liquid value, in both membranes at 35 °C. When plotted against water volume fraction, the gas permeability increases exponentially in the range between 2% and 20%; the slope of the curve is higher for Nafion^® than for Aquivion^®, as it is reasonable due to their different microstructures. The ideal selectivity of the two membranes for He over N₂, O₂ over N₂ and He over O₂, decreases markedly with increasing water content in the membrane.     

Effects of sodium and zinc neutralization on large deformation hysteresis of an ethylene methacrylic acid butyl acrylate copolymer

The mechanical hysteresis and recovery behaviors of an elastomeric ethylene methacrylic acid butyl acrylate (EMAABA) copolymer, its sodium-neutralized (EMAABA_Na) and zinc-neutralized (EMAABA_Zn) counterparts are evaluated and compared under large strain loading conditions. Experiments at different rates, under cyclic loading conditions and in relaxation indicate two major hysteresis mechanisms: a characteristic viscoelastic mechanism operative at all strains and a microstructural evolution/breakdown mechanism incurred during large strains. Loading-unloading cycles show large rate-dependent hysteresis loops with significant recovery of strain upon unloading, revealing a highly dissipative yet resilient behavior. The microstructure breakdown mechanism occurs during the initial strain excursion as revealed by subsequent loading cycles showing a significantly more compliant behavior and dramatically reduced hysteresis loops. The neutralized materials are found to be significantly stiffer, stronger and more dissipative compared to the neat material while still retaining the same level of recovery. Therefore the neutralization of this material provides an excellent means to tune stiffness and dissipation while retaining resilience, providing mechanical performance properties attractive for abrasion, impact and puncture resistant applications.     

New polymer electrolytes based on ether sulfate anions for lithium polymer batteries: Part I. Multifunctional ionomers: Conductivity and electrochemical stability

New lithium conducting ionomers based on commercial polyethers were synthesized by chemical modification in order to incorporate not only the anionic function on the polymer backbone but also polar aprotic and (or) protic groups improving both the salt dissociation and the anion-solvating ability of the multifunctional copolymers. The choice of environmentally friendly rather than perfluorinated anionic functions did not appear to compromise for the ionic conductivity. Lastly, the preliminary results on the use of an electrochemically stable and relatively cheap additive sparteine appear promising and could be generalized to a variety of polymer electrolytes for lithium batteries.     

Extrusion: An environmentally friendly process for PEMFC membrane elaboration

The paper deals with the use of extrusion to process PEMFC filled and unfilled membranes. Several routes including the sulfonation of filled and unfilled extruded membranes and the extrusion of filled and unfilled ionomers are reported. Thanks to the use of selected water-soluble aid process plasticizers, acid and alkaline forms of sulfonated polyethersulfone were, for the first time, successfully extruded. The extrusion process did not lead to any degradation of the ionomer performances. Decreasing the membrane cost while using environmentally friendly elaboration conditions, it should be helpful to an industrial production. In addition, avoiding filler sedimentation it should allow homogeneous composite membranes to be obtained.     

A molecular dynamics simulation study of the influence of free surfaces on the morphology of self-associating polymers

Molecular dynamics simulations of thin films and bulk melts of model self-associating polymers have been performed in order to gain understanding of the influence of free surfaces on the morphology of these polymers. The self-associating polymers were represented by a simple bead-necklace model with attractive groups (stickers) at the chain ends (end-functionalized polymer) and in the chain interior (interior-functionalized polymer). The functionalized groups were found to form clusters in the melt whose size is representative of that found experimentally in many ionomer melts. While the size distribution and shape of the clusters in the thin films were found to be relatively unperturbed compared to their corresponding bulk melts, the morphology of the self-associating melts was found to be significantly perturbed by the free surfaces. Specifically, a strong depletion of stickers near the interface and the emergence of clearly defined layers of stickers parallel to the surface was observed. Increased bridging of clusters by the functionalized polymers was also observed near the free surface. We conclude that these effects can be associated with a high free energy for stickers in the low-density interfacial regime: stickers prefer to be in the higher-density interior of the film where relatively unperturbed sticker clusters can form.     

Small angle neutron scattering from ionomer gels

Small angle neutron scattering intensities for sols and gels of the physically associating ionomer 1.39 mol% sodium sulphonated polystyrene with molecular weight 10⁵ g/mole in xylene have been obtained over a broad wavevector (q) and concentration range. In the low q and concentration range the scattering behaviour of this ionomer/solvent system can quite readily be interpreted using the open association aggregation model. In more concentrated solutions and at higher q, however, interpretation of the scattering behaviour for polymers associating via an open association mechanism (OAM) is more difficult, particularly if, as in this investigation, the single chains and aggregates have varying densities and fractal parameters. In this study various methods have been developed to interpret the low and high q scattering from systems whose extent of aggregation can be modelled using the OAM. Using these methods it has been possible to confirm that the open association model can be used to interpret the extent of aggregation of the above ionomer in xylene even after the solutions appear to be gelled. Single ionomer chains within both the dilute solutions and gels were found via modelling to have a radius of gyration of 60 Å, which compares with dimensions of 25 Å and 93 Å calculated for a solid sphere of polystyrene or an unperturbed polystyrene Gaussian coil, respectively. The aggregates, however, all had radii of gyration comparable with what would be expected for polystyrene of the aggregate molecular weight in an unperturbed state. These results suggest that gelation of ionomer solutions at particular concentration thresholds is not due to an abrupt change in the aggregate structures at some critical concentration but occurs as a result of interactions between the very large aggregates that the OAM predicts should gradually form as the ionomer concentration increases.     

Synthesis and thermal properties of telechelic poly(lactic acid) ionomers

Telechelic poly(lactic acid) (PLA) ionomers were synthesized using a chemical recycling process. A transesterification reaction between a commercial PLA and 2-hydroxyethyl methacrylate or ethylene glycol was used to produce a hydroxy-terminated PLA. The hydroxy-terminated PLA was then reacted with itaconic anhydride to produce terminal carboxylic acid groups, which were neutralized with appropriate metal acetates to produce Na-, Li-, K-, Zn-, Ca- and Y-ω- and α,ω-telechelic PLA ionomers. ¹H NMR spectroscopy was used to confirm the presence of the itaconic acid end-groups and FTIR spectroscopy was used to quantify the extent of neutralization. The addition of the ionic groups increased the glass transition (T_g), and T_g increased as the strength of the ion-pair increased. The ionic groups suppressed crystallinity, especially when multivalent cations were used.     

Influence of Diisocyanate Structure on the Synthesis and Properties of Ionic Polyurethane Dispersions

A number of aqueous polyurethane dispersions based on polytetramethylene glycol (PTMG), 1,4-butanediol (1,4-BDO), dimethylol propionic acid (DMPA) and diisocyanates of differing structures such as toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane diisocyanate (H₁₂MDI) were prepared. IR Spectroscopy was used to check the end of polymerization reaction and also the polymer characterization. The effects of diisocyanate structure on the particle size, contact angle, mechanical and thermal properties of the emulsion-cast films were studied. Average particle size of prepared polyurethane emulsions change by different diisocyanate based polyurethane. TDI based PU shows higher average particle size and contact angle than the others. Tensile strength, hardness, and elongation at break were higher in the case of MDI based polyurethane. Thermal property and thermal stability is also affected by variation of diisocyanate molecular structure.