A SOLID-STATE NMR-STUDY OF MICROPHASE STRUCTURE AND SEGMENTAL DYNAMICS OF POLY(STYRENE-B-METHYLPHENYLSILOXANE)DIBLOCK COPOLYMERS

Solid-state n.m.r. techniques have been used to study the microphase structure of poly(styrene-b-methylphenylsiloxane) (PS-b-PMPS) diblock copolymers with different compositions and molecular weights. The proton n.m.r. spectra display motionally narrowed lines of the PMPS component at ambient temperatures. The mobility of the segments in the copolymers is different, however, from that in the homopolymer. This can be related to the shift of the glass transition temperature (T(g)) for the siloxane-rich phase, not detected by d.s.c. By measuring the proton spin diffusion with C-13 detection-combining a dipolar filter with line-narrowing techniques-the microdomain dimensions have been evaluated quantitatively. The results are compared with determination of the phase separation by SAXS and TEM. It is shown that solid-state n.m.r. is able to detect heterogeneities on a scale as small as 2nm in systems that exhibit only a single T(g) in the d.s.c. measurement. In addition, an interphase in the phase-separated PS-b-PMPS systems is revealed by spin diffusion measurements and confirmed by two-dimensional heteronuclear wideline separation n.m.r. spectroscopy.