Super ²- Structures in Polydisperse Multiblock-Copolymers

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

Abstract
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 , and is much larger than the size of ordinary microdomains if is small. The theoretical description involves the second order parameter field (in addition to the normal order parameter 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.