Liquid polyethylene glycol dispersed in a poly(styrene)-b-poly(ethylene/butylene)-b-poly(styrene) elastomer: determination of morphology and molecular mobility by light and electron microscopy as well as nuclear magnetic resonance self-diffusion andT2 measurements

Abstract

An emulsion of liquid polyethylene glycol (PEG) in a rubbery poly(styrene)-b-poly(ethylene/butylene-b-poly-(styrene) (SEBS) matrix was prepared using a poly-(butadiene-b-poly(ethylene oxide) (PB-b-PEO) diblock copolymer as emulsifier. In addition to its emulsifying effect, it was shown that a block copolymer containing a crystalline PEO sequence has a tendency to form micelles as well as supramolecular structures in form of square platelets when they are solubilized in nonpolar solvent such as methylcyclohexane. The filmification of the emulsion by solvent evaporation and the film morphology were examined by light and electron microscopy and by nuclear magnetic resonance (NMR) T2 and self-diffusion measurements. Microscopic evaluations have shown cavities having an average size, depending on the copolymer content, of a few micrometers and filled with liquid PEG. Additionally, smaller structures typically in the range of 30–50 nm have been observed by transmission electron microscopy and are attributed to crystalline lamellae formed by the copolymer in the matrix. The T2 measurements reveal three contributions to the transverse magnetization decay: one of the SEBS matrix, one of the liquid within the cavities and one of the liquid dissolved in the smaller structures formed by the copolymer in the matrix. In the pulsed field gradient NMR self-diffusion experiments two self-diffusion coefficients were found, one of the liquid in the cavities and one of the liquid dissolved in the matrix within the smaller structures. Generally, a restricted diffusion is observed in that latter case owing to confining structures for the diffusing liquid molecules. © 1998 John Wiley & Sons, Ltd.