Viscoelastic properties and morphology of sulfonated poly(styrene-b-ethylene/butylene-b-styrene) block copolymers (sBCP), and sBCP/[silicate] nanostructured materials

Self-assembled organic/inorganic hybrid materials were created via domain targeted sol-gel reactions of tetraethylorthosilicate in solution with sulfonated poly(styrene-b-ethylene-co-butylene]-b-styrene) (sSEBS) copolymers. Dynamic mechanical analyses (DMA) of these hybrid materials suggest that the silicate component preferentially incorporates within the sulfonated polystyrene (PS) domains. An irreversible order-order transition (OOT) for unmodified SEBS, sSEBS, and the organic/inorganic hybrids was identified using DMA in shear mode. The OOT temperature increases with sulfonation as well as by adding a silicate phase by the sol-gel process. The DMA results imply a morphological shift with sulfonation, and reflect modified interactions within and between phases. Atomic force microscopy (AFM) indicated a shift from hexagonally packed cylinders in unmodified SEBS to a lamellar morphology in the sulfonated materials, but silicate incorporation did not affect the morphology or domain dimensions. The latter result is evidence for sol-gel polymerization templating in a self-assembly process. The phase-separated morphology is stable up to the degradation temperature of the polymer and thermogravimetric analysis revealed that the degradation temperature is unaffected by silicate incorporation. Small angle X-ray scattering data are in harmony with the structures revealed by AFM in terms of degree of order and scale of features. These results are largely rationalized in terms of chain mobility restrictions due to hydrogen-bonding interactions between different sulfonated PS blocks, an increase in the PS-ethylene/butylene block mixing parameter, increased interfacial surface tension and chain restrictions posed by inserted silicate nanostructures in the case of the hybrid materials.