Homopolymers containing ionic moieties such as sulfonic acid groups are suitable as fuel-cell, waterpurification and ion-exchange membranes or, alternatively, as electroactive or otherwise stimuliresponsive soft materials. Block ionomers constitute a class of ionomers in which (i) long sequences of repeat units are sufficiently incompatible to microphase-separate and (ii) at least one sequence possesses ionic groups along its backbone. In this study, the midblock of a model poly(p-tert-butylstyrene-bstyrene-b-p-tert-butylstyrene) (TST) triblock copolymer has been selectively sulfonated to different degrees by reaction with acetyl sulfate. Self-assembly of the unaffected endblocks prevents the resultant block ionomers from dissolving in water and imparts water-swollen ionomer films with sufficient mechanical integrity to remain intact. The degree of sulfonation is controlled by varying the concentration of acetyl sulfate, as confirmed by spectroscopic analyses. An increase in ionic content promotes a reduction in thermal stability due to sulfonic acid cleaving, but a significant increase in water sorption that increases with increasing temperature. Although the parent TST copolymer is disordered according to small-angle X-ray scattering, moderate levels of midblock sulfonation induce microphase ordering and simultaneously increase the intermicrodomain distance due to swelling considerations.

Selective sulfonation of a poly[styrene-b-butadiene-b-styrene] (SBS) triblock copolymer has been performed with a sulfur trioxide-dioxane (SO 3 -dioxane) complex to generate midblock-sulfonated triblock ionomers possessing varying degrees of sulfonation (DOS). Products of the sulfonation reaction have been characterized by proton nuclear magnetic resonance and Fourier-transform infrared spectroscopies to ensure sulfonation only involves the B midblocks. Due to this targeted sulfonation, the lower glass transition temperature (T g ) disappears completely in all the ionomers examined, indicating that the formation of ionic aggregates restricts the mobility of the B midblocks. Such aggregates hinder microphase separation and promote a diffuse interface, as established by progressive broadening of the upper T g with increasing DOS. Additional evidence of diffuse interfaces and matrix densification is provided by small-angle X-ray scattering, which reveals a concurrent size reduction in microdomain spacing with increasing DOS. A sulfonation-induced order-order morphological transition from cylinders to lamellae is likewise observed. Due to the retention of microphase-separated glassy microdomains that serve as physical crosslinks, these triblock ionomers are capable of absorbing remarkably high solvent levels and forming highly swollen gel networks in polar media, thereby making them suitable for use in hygiene and healthcare applications, as well as in devices requiring ion transport.

Highly electron deficient monoaryl, di-aryl and bis-diaryl acetonitriles were effectively synthesized using either a nucleophilic aromatic substitution (NAS) or a palladium-mediated coupling pathway. Synthesis of di-aryl acetonitriles most conveniently proceeded via NAS--palladium-mediated coupling was not required. This reaction, however, results in a product that is more acidic than the reactants. Facile deprotonation of the product prevents efficient formation of the bis-diaryl acetonitrile through a NAS pathway. Thus, palladium-mediated coupling is required to prepare the bis-diaryl acetonitrile efficiently. In the palladium-catalyzed coupling, choice of base and solvent (and thus the counter cation for the benzylic anion nucleophile) is important. Also, choice of the supporting ligand is important, indicating the sensitivity of the reaction to steric and ligand electronic effects.