Pierre Hoerner

Emulsification of poly(ethylene glycol) in thermoplastic elastomers by using polybutadiene-block-poly(ethylene oxide) diblock copolymers as stabilisers. Determination of the liquid phase mobility by pulsed field gradient NMR

Polymeric film materials comprising a continuous elastomer phase of a styrene-hydrogenated diene thermoplastic elastomer (SEBS) and a dispersed liquid phase of poly(ethylene glycol) (PEG) were prepared by starting from an emulsion of PEG dispersed as small droplets in a solution of SEBS in methylcyclohexane. A polybutadiene-block-poly(ethylene oxide) block copolymer is used as emulsifier and stabiliser for these emulsions. The particle size of the dispersed PEG phase, in the emulsion, and in the final film obtained by solvent evaporation could be adjusted as a function of the block copolymer concentration. The morphology of the material was studied by scanning electron microscopy (SEM) and pulsed field gradient (PFG) NMR. From the diffusion coefficients determined by PFG NMR it is demonstrated that a part of the block copolymer, in addition to its stabilisation effect, has a tendency to form in the rubber matrix micelles and aggregates (polymolecular micelles) which are able to solubilize a given fraction of PEG.

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

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.