J. Phys. II France
Volume 7, Numéro 10, October 1997
Page(s) 1489 - 1497
DOI: 10.1051/jp2:1997197
J. Phys. II France 7 (1997) 1489-1497

Super 2- Structures in Polydisperse Multiblock-Copolymers

A.N. Semenov1, 2

1  Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK
2  Nesmeyanov Institute of Organo-Element Compounds of Russian Academy of Science, 28 Vavilova Str., Moscow 117812, Russia

(Received 31 January 1997, revised 29 May 1997, accepted 6 June 1997)

Microphase separation in multiblock (AB) n copolymer melts at equilibrium is considered theoretically. It is shown that any finite polydispersity of the block molecular weights results in a set of novel super 2-structures which are characterized by two levels of microdomains, one on the top of the other. The typical size of the second-level microdomains is governed by the polydispersity degree $\delta$, and is much larger than the size of ordinary microdomains if $\delta$ is small. The theoretical description involves the second order parameter field $\varphi(r)$ (in addition to the normal order parameter $\psi$ related to the local composition) which is proportional to the local excess of longer blocks over shorter blocks. A scaling picture including the main characteristics of the super 2-structures is built for both weak and strong segregation regimes.

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