Phase Behavior and Properties of ABC Triblock Copolymers

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9905008BatesLinear ABC triblock copolymers are characterized by a complex, and relatively poorly defined, spectrum of equilibrium and non-equilibrium morphologies. Phase behavior in this class of macromolecules is governed by three segment-segment interaction parameters, two independent composition variables, and three sequence possibilities (ABC, ACB, BAC), leading to a daunting array of experimental configurations for each specified trio of polymers. This project will address two aspects of ABC block copolymer phase behavior: (i) the role of metastability in the vicinity of the order-disorder transition, and (ii) the stability range and various physical properties of triply periodic and multicontinuous microstructures. Three model systems will be synthesized for these purposes: ISD (and SID), ISO (and SIO), and VPE (and PVE) where I, S, D, O, P, V, and E represent poly(isoprene), poly(styrene), poly(dimethysiloxane), poly(ethyleneoxide), poly(ethylenepropylene), poly(vinylcyclohexane), and poly(ethylene), respectively. Anionic polymerization and composition while yielding sizable (ca 100g) batches of material. Phase behavior will be established through a combination of dynamic mechanical spectroscopy, small-angle x-ray scattering (SAXS), and transmission electron microscopy (TEM). In the first thrust area, initially disordered triblocks will be cooled into the ordered regime and the resulting sequences of ordered phases will be characterized. The kinetics of order-order transitions will be assessed and correlated with the occurrence of trapped (metastable) states. Guided by preliminary findings with the ISD system, the pentacontinuous core-in-shell Gyroid phase will be mapped as a function of composition (f1 and fs), and evaluated for universality using SIO and VPE (or PVE) triblocks in the second thrust area. Self-consistent mean-field theory calculations will direct the selection of the most promising molecular parameters for material synthesis. Microdomain continuity will be probed by ionic conductivity in salt-doped SIO while mechanical properties will be assessed using the saturated hydrocarbon triblocks that contain glassy (V), semicrystalline (E), and rubbery (P) blocks.Block copolymers are a class of materials that bring together chemically distinct polymers, and the associated properties, in single hybrid macromolecules. This research project will focus on synthesizing new combinations of three chemically distinct polymer blocks, known as ABC triblock copolymers, and characterizing the resulting microstructures and physical properties. Targeted applications for these new materials include membranes and high strength plastics.