Incorporation of Metallic Species into Midblock-Sulfonated Block Ionomers.

Block ionomers can, in the same fashion as their neutral block copolymer analogs, microphase-order into various nanoscale morphologies. The added benefit of a copolymer possessing a charged species is that the resultant block ionomer becomes amphiphilic and capable of imbibing polar liquids, including water. This characteristic facilitates incorporation of metallic species into the soft nanostructure for a wide range of target applications. In this study, the nonpolar and polar constituents of solvent-templated midblock-sulfonated block ionomers (SBIs) are first selectively metallated for complementary morphological analysis. Next, four different salts, with cationic charges ranging from +1 to +3, are introduced into three hydrated SBIs varying in their degree of sulfonation (DOS), and cation uptake is measured as a function of immersion time. These results indicate that uptake generally increases with increasing salt concentration, cationic charge, and specimen DOS. Swelling and nanoindentation measurements conducted at ambient temperature demonstrate that water uptake decreases, while the surface modulus increases, with increasing cationic charge. Chemical spectra acquired from energy-dispersive X-ray spectroscopy (EDS) confirm the presence of each of the ion-exchanged species, and corresponding EDS chemical maps reveal that the spatial distribution of these species is relatively uniform throughout the block ionomer films.

Ionic complexation of endblock-sulfonated thermoplastic elastomers and their physical gels for improved thermomechanical performance.

Thermoplastic elastomers (TPEs) composed of nonpolar triblock copolymers constitute a broadly important class of (re)processable network-forming macromolecules employed in ubiquitous commercial applications. Physical gelation of these materials in the presence of a low-volatility oil that is midblock-selective yields tunably soft TPE gels (TPEGs) that are suitable for emergent technologies ranging from electroactive, phase-change and shape-memory responsive media to patternable soft substrates for flexible electronics and microfluidics. Many of the high-volume TPEs used for these purposes possess styrenic endblocks that are inherently limited by a relatively low glass transition temperature. To mitigate this shortcoming, we sulfonate and subsequently complex (and physically crosslink) the endblocks with trivalent Al3+ ions. Doing so reduces the effective hydrophilicity of the sulfonated endblocks, as evidenced by water uptake measurements, while concurrently enhancing the thermomechanical stability of the corresponding TPEGs. Chemical modification results, as well as morphological and property development, are investigated as functions of the degree of sulfonation, complexation and TPEG composition.

Spectroscopic and Rheological Cross-Analysis of Polyester Polyol Cure Behavior: Role of Polyester Secondary Hydroxyl Content.

The sol-gel transition of a series of polyester polyol resins possessing varied secondary hydroxyl content and reacted with a polymerized aliphatic isocyanate cross-linking agent is studied to elucidate the effect of molecular architecture on cure behavior. Dynamic rheology is utilized in conjunction with time-resolved variable-temperature Fourier-transform infrared spectroscopy to examine the relationship between chemical conversion and microstructural evolution as functions of both time and temperature. The onset of a percolated microstructure is identified for all resins, and apparent activation energies extracted from Arrhenius analyses of gelation and average reaction kinetics are found to depend on the secondary hydroxyl content in the polyester polyols. The similarity between these two activation energies is explored. Gel point suppression is observed in all the resin systems examined, resulting in significant deviations from the classical gelation theory of Flory and Stockmayer. The magnitude of these deviations depends on secondary hydroxyl content, and a qualitative model is proposed to explain the observed phenomena, which are consistent with results previously reported in the literature.