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Published February 24, 1997 | public
Journal Article

Dynamics of Disordered Diblocks of Polyisoprene and Polyvinylethylene


The apparent thermorheological simplicity of disordered diblocks is reconciled with the failure of time−temperature superposition of corresponding miscible blends by examining the relaxation of the constituent blocks using rheo-optical techniques. Diblocks of 1,4-polyisoprene (PIP) and polyvinylethylene (PVE) are examined over a range of temperatures for two compositions (φ_(PIP) = 0.25 and 0.75). Unlike blends of PIP and PVE, the block copolymers appear to obey time−temperature superposition on the basis of their viscoelastic properties. However, departure from thermorheological simplicity is exposed in their stress−optical behavior. In particular, the copolymer rich in the high T_g component (φ_(PIP) = 0.25) shows distinct temperature dependencies for the individual blocks, in accord with the behavior of PIP/PVE blends. The block copolymer rich in the low T_g component (φ_(PIP) = 0.75) is thermorheologically simple because both blocks have similar monomeric friction coefficients ζ_(o,PVE) ≈ ζ_(o,PIP), again in accord with prior results on PIP/PVE blends. The failure of time−temperature superposition in these diblocks was not previously observed because the change in ζ_(o,PVE)/ζ_(o,PIP) with temperature produces subtle changes in the overall relaxation spectrum relative to a linear chain of uniform friction.

Additional Information

© 1997 American Chemical Society. Received June 21, 1996; Revised Manuscript Received December 3, 1996. We gratefully acknowledge the support of the National Science Foundation Presidential Young Investigator Award (J.A.K.), the National Physical Science Consortium (B.H.A.), the Caltech Summer Undergraduate Research Fellowship Program (K.S.), Chevron, and the Caltech Consortium in Chemistry and Chemical Engineering:  E. I. du Pont de Nemours and Company, Inc. and Eastman Kodak Company. We thank Dr. Fei Wang for preparing and characterizing the polymers

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