MICROSTRUCTURAL CHARACTERISTICS OF STRONGLY-SEGREGATED AXB TRIBLOCK TERPOLYMERS POSSESSING THE LAMELLAR MORPHOLOGY

While several theoretical formalisms exist which are capable of providing valuable insight into the molecular organization responsible for periodic morphologies in strongly-segregated diblock, triblock, and starblock copolymers possessing A and B monomers, few efforts have specifically addressed materials consisting of more than two different monomer species. In this work, a self-consistent field formalism, based on concepts developed for AB diblock and ABA triblock copolymers, is proposed for strongly-segregated AXB triblock terpolymers. Here, X denotes either a third, chemically dissimilar (C) monomer species or a random (A/B) segment composed of both A and B monomer units. Analytical expressions for the free energy and microdomain periodicity at equilibrium have been obtained for the lamellar morphology in terms of pairwise interaction parameters (chiAX and chiBX), chain length (N), and molecular composition (f(x)). The microdomain periodicity of ordered AXB terpolymers is predicted to exhibit the same N2/3 scaling behavior as that of AB diblock copolymers and is also found to decrease initially with f(x), suggesting that relatively short midblocks enhance microphase mixing.