Eur. Phys. J. E 7, 49-64 (2002)
DOI: 10.1140/epje/i200101101
Phase equilibria in random multiblock copolymers
A.V. Subbotin1 and A.N. Semenov21 Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow 117912, Russia
2 Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK
a.semenov@leeds.ac.uk
(Received 13 July 2001)
Abstract
A mean-field theory for domain structures in random
multiblock copolymer melts is developed. We focus on the finite
molecular weight effects resulting in a competition between
macroscopic phase separation and microdomain formation in the
system. We identify an essential parameter
controlling the phase behavior of the system, where
N is the number
of blocks per chain and
is the composition asymmetry
parameter
(= the difference between the mean copolymer composition
and its critical value). The phase diagram involving
and the reduced temperature as variables is
obtained. The regions of coexistence of two or more phases are
identified. We show that a superstructure formation on cooling is
always pre-empted by a macroscopic phase separation of the
macroscopically homogeneous (disordered) system yielding two
homogeneous phases:
. The third (lamellar) phase
separates on further cooling. Then hexagonal and body-centred-cubic
phases take over if
. As the Flory
interaction parameter
increases further, the standard
transitions
take place.
36.20.-r. - Macromolecules and polymer molecules.
61.25.Hq - Macromolecular and polymer solutions; polymer melts; swelling.
61.41.+e - Polymers, elastomers, and plastics.
36.20.Ey - Conformation (statistics and dynamics).
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002