2007 Volume 64 Issue 5 Pages 286-293
Molecular motion of end segments of polystyrene chains in polystyrene(PS)-b-poly(methyl acrylate) (PMA) forming phase-separated structures of spherical, cylindrical, and lamellar morphology was investigated by ESR spin-label method. The PMA volume fraction was kept below 55% to have PS block constitute a matrix component. Phase-separated structures of PS-b-PMA were confirmed by SAXS. No phase-transition was observed in the temperature range employed in the present study. In bulk PS, the free volume around the chain end is relatively large, and the segmental mobility around chain ends is generally high. In the block copolymer, the molecular mobility around PS end segments was also found to be higher than that around inner PS segments. Moreover, the difference in transition temperature between the end and inner segments was larger than that in bulk PS. These results are considered to be related to the conformation of PS chains in the phase-separated structures. Chain ends in a microdomain have been theoretically and experimentally shown to be populated more around the center of the microdomain. This effect of chain end segregation activates molecular motion around the PS end segments. The segregation effect depends on the morphology and influences the mobility around the chain ends.
