This grant is jointly funded by the Polymer Program in the Division of Materials Research and the Organic Synthesis Program in the Division of Chemistry. Heteroarm star polymers containing x arms of monomer A and n-x arms of monomer B should exhibit unusual segregation and interphase phenomena. Living linking reactions will be used to synthesize A2B2 star polymers composed of polystyrene and polydiene arms, and a new general fluorescent-labeling chemistry will be utilized to attach pyrene, anthracene, and naphthalene groups at the termini of the arms. A series of heteroarm star copolymers with well-defined structures will be used to explore their unique dynamic and equilibrium properties in the solid state, in the melt, and in solution. The consequences of interarm interactions in isolated heteroarm stars will be assessed from the rates and equilibrium for macrocyclization, as deduced from excimer emission by molecules in which two arms bear pyrene or naphthalene groups at their free ends. Discrimination between the various types of interarm interactions that can occur in semidilute solution, melts, and in the solid state will be determined with heteroarm stars selectively labeled for the study of excimer emission or the rate of Forster transfer. The dynamics of isolated heteroarm stars, and their diffusion in concentrated solutions and melts, will be determined using pulsed-gradient spin-echo NMR.
