Organization and orientation of a triblock copolymer poly(ethylene glycol)-b-poly(p-phenylene ethynylene)-b-poly(ethylene glycol) and its blends in thin films

Molecular organization and orientation in thin films (∼100 nm) of a triblock copolymer, PPEPEG composed of a rigid, π-conjugated middle block poly(phenyleneethynylene), PPE, and two poly-(ethylene glycol) end blocks, PEG, were studied by fluorescence, secondary ion mass spectroscopy (SIMS), and atomic force microscopy (AFM). Fluorescence polarization studies of the triblock copolymer and its blends with poly(methyl methacrylate) (PMMA) led to the conclusion that the triblock copolymer molecules were oriented perpendicularly to the silicon substrate surface. Orientation of molecules in the vertical direction was confirmed by measurement of the oxygen depth profile of the film with the use of SIMS. Copolymer molecules in large fraction of PMMA (∼2 wt % in PMMA) were molecularly dispersed to give rise to high fluorescence emission intensity at a wavelength characteristic of nonaggregated chains. The reinforced action of this rigid polymer for PMMA was obtained. The secant modulus of the 2 wt % blend in a tensile test was 5.7 times the value of PMMA.