(420a) High Temperature Thermoplastic Elastomer Gels

Block copolymers are of great scientific and commercial interest primarily due to their inherent ability to assemble into well-defined nanostructures in a wide range of emerging applications, such as drug delivery, microelectronics, and organic photovoltaic devices. However, most block copolymers are neutral charge and hydrophobic, in which case, chemical modification can be used as a powerful approach to introduce hydrophilicity to non-polar blocks. To our special interest, the sulfonation of endblocks of styrenic thermoplastic elastomers (TPEs), that was firstly establish by Weiss and coworkers, can yield high hydrophilicity and enable high ion and water transport. The sulfonated block copolymers, generally classified as block ionomers, are capable of being applied into target applications, such as fuel cells, ion-conducting membranes, and electron transport. The strong sulfonate groups of sulfonated polymers can provide opportunities for generating chemically cross-linked networks by incorporating metallic species.

Neutralized block ionomers, obtained via inorganic salts incorporation into the sulfonated block ionomers, exhibit unique thermal properties of forming crosslinks, by which means the thermal and mechanical properties of these materials can be altered. The neutralization generally involves an ion exchange process that replaces the protons on the sulfonic acid moieties with metal cations. A wide range of metallic species with different cationic valencies can be used for neutralization, specifically, interest in multivalent neutralization of ionomers continues to grow due to their potential applications in gas separation and facilitated transport membranes.

In this study, we reported high temperature thermoplastic elastomer gels (TPEGs) based on neutralized sulfonated block copolymers, that were prepared by neutralizing the sulfonated poly [styrene-b-(ethylene-co-butylene)-b-styrene] (sSEBS) with aluminum chloride salts. The trivalent Al³⁺ ions formed ionic bonds between three sulfonic acid groups, providing cross-links in the network. The ion-rich nanodomains provide a physical network that imparted superior thermomechanical properties. The effects of aluminum neutralization on water uptake ability, polymer morphology, mechanical properties, and thermal stabilities were explored. Small-angle X-ray scattering performed at ambient temperature confirmed a morphology change from lamellar of neat block ionomers to hexagonal-close-packed of TPEGs. Rheology tests were carried out to further confirm the gel behaviors of these materials with mineral oil addition. The mechanical results demonstrate the TPEGs with 70% solvent still remain high tensile strength and toughness. The glass transition temperature (Tg) of the TPEGs cannot be observed up to 250 ℃, indicating that the TPEGs are completely thermally stable as high temperature materials. These results are correlated with thermal and mechanical property measurements from rheology and dynamic mechanical analysis to elucidate the neutralization on TPEGs and establish structure- property relationships.