J. Dudowicz et Kf. Freed, Explanation for the unusual phase behavior of polystyrene-b-poly(n-alkyl methacrylate) diblock copolymers: Specific interactions, MACROMOLEC, 33(14), 2000, pp. 5292-5299
The observed variation in the nature of the order-disorder transition (lowe
r vs upper temperature phase diagram) with the length of the n-alkyl side g
roup in polystyrene-b-poly(n-alkyl methacrylate) diblock copolymers [PS-b-P
(nAMA)] by Mayes, Russell, and their co-workers (Macromolecules 1998, 31, 8
509) is explained using a simple version of the lattice cluster theory that
distinguishes between specific interactions of different united atom group
s and that determines the temperature-independent portion of the effective
Flory interaction parameter chi solely from the monomer molecular structure
s without employing adjustable parameters. The presence of this temperature
independent part of chi provides the entropic driving force for the lower
disorder-order transition in systems with negative enthalpic chi. The only
adjustable parameters of the theory are three independent combinations of t
he specific interaction energies. The theory is developed for arbitrary mon
omer structures of the two block components (or alternatively for two homop
olymer blend species) and is extended to describe A-b-CxD1-x diblock copoly
mers in which one block is a random copolymer. The calculated disorder-orde
r transition temperatures accord reasonably with experimental data, and the
utility of the theory is illustrated further by presenting predictions of
how the phase behavior of the PS-b-P(nAMA(x)-co-n'AMA(1-x)) systems changes
with n and n' and with the random copolymer composition x.