MOLECULAR-WEIGHT DEPENDENCE OF THE TRACER DIFFUSION-COEFFICIENT OF SHORT CHAINS IN THE MICROPHASE DOMAIN OF BLOCK-COPOLYMERS AS STUDIED BY THE PULSED-FIELD GRADIENT NUCLEAR-MAGNETIC-RESONANCE METHOD

By means of the pulsed-field gradient nuclear magnetic resonance metho d, the tracer diffusion of homopolymer chains dissolved in the microph ase domain of block copolymer mesophase has been studied for two syste ms: poly(dimethylsiloxane) (PDMS) in polystyrene(PS)-b-PDMS in the pre sence of d(6)-benzene as a plasticizer, and poly(ethylene glycol) (PEG ) in PS-b-poly(hydroxystyrene-g-PEG)-b-PS. Comparing the diffusion coe fficient D of the tracers in the block copolymer matrices with the sel f-diffusion coefficient D-s of the pure tracers, two regimes with a di fferent dependence of D/D-s on the molecular weight M of the tracers h ave commonly been found in the two systems. In the lower M regime (reg ime I), the ratio D/D-s increased remarkably with increasing M, wherea s in the higher M regime (regime II), the value of D/D-s was similar t o 0.15 and was independent of M. This behaviour could be explained by the M dependence of the spatial distribution of the tracer chains in t he microphase domain. In regime I, the tracers deeply penetrate into t he brushes of the PDMS or grafted PEG with the depth decreasing with i ncreasing M, while in regime II the tracer chains do not penetrate wel l into the PDMS or PEG brushes, but rather are interposed between the layers.