Segment Dispersity Effects in Block Copolymer Self-assembly

     Modern polymerization techniques enable syntheses of functional block copolymers with unusual thermal, electronic, and ionic conductivities. However, these new macromolecular syntheses often introduce significant molar mass dispersity (a chain length heterogeneity) into one or more of the copolymer blocks. Conventional wisdom stipulates that chain length uniformity (“monodispersity”) is a prerequisite for periodic nanoscale self-assembly of block copolymers. Few studies have questioned the validity and stringency of this preconceived notion.

     We are studying the melt-phase behavior of ABA-type triblock copolymers comprising either polydisperse A or B blocks. Contrary to conventional wisdom, polydisperse ABA BCPs also assemble into a rich array of periodic nanoscale structures with unexpectedly enhanced thermodynamic stabilities as compared to their monodisperse analogs. Based on these insights, we are now studying (1) a series of new Li-ion conducting block copolymers for advanced batteries, as well as (2) new high chi/low N multiblock polymers

    In lithium salt-doped poly(styrene)/poly(ethylene oxide) multiblock polymers, we recently demonstrated that poly(ethylene oxide) segment dispersity shifts the lamellar morphology window to higher salt-doped poly(ether) segment contents without substantially changing the location of the thermally-induced order-to-disorder transition. Ongoing studies focus on understanding how dispersity impacts the temperature-dependent ionic conductivities of these materials.