Supramolecular assembly in telechelic polymer blends

Abstract

Equilibrium, supramolecular assembly in melt blends of two species of telechelic polymers with reversible bonding sites at both ends is theoretically investigated. The bonding between polymers, whether between like or dislike chains, is controlled by affinities of chain bonding set by specified bond energies. Low affinities, or low overall bond strength, results in a monodisperse population of unlinked chains while larger affinities cause longer chains to assemble, forming a polydisperse blend. We investigate sequentially blends with only homobonding (like chain), only heterobonding (dislike chain), and finally a mixed homo- and heterobonding melt. In the first case, the effects of longer chain assembly and polydispersity in a homogeneous melt and its bulk demixing transition are explored. In contrast with the homobonding case, large heterobonding affinities cause alternating blocks to assemble into multiblock copolymers, which can lead to mesophases. The weak bonding region between bulk phase separation and mesophase stability is investigated and a novel Lifshitz point is found indicating a region prone to emulsify. Mixed homo- and heterobonding systems are also examined. Polymeric segments of both species are modeled as flexible Gaussian threads and nonspecific interactions between dissimilar blocks are contactlike Flory-Huggins repulsions. The melts are assumed to be incompressible and all calculations are carried out within mean-field theory. A new integral equation formalism is developed for enumerating all linear species in these complex supramolecular systems, and the random phase approximation and numerical self-consistent field theory are invoked in this context to map out a variety of phase diagrams.