While much of what is known of the self-assembly behavior of amphiphilic polymers springs from studies of A-B diblock copolymers comprised of flexible blocks, highly branched polymers or those that are locally stiff are interesting because topological constraints may affect aggregation behavior through conformational entropy and molecular packing. Using polystyrene-block-poly(1,3-cyclohexadiene) (PS-b-PCHD) copolymers, we examine how changing the rigidity by varying the PCHD block microstructure affects self-assembly. Spherical micellar aggregates are observed when the CHD repeat units are predominantly connected through 1,4 linkages and ill-formed aggregates seen when the ratio of 1,4/1,2 linkages is near unity. Between these limits, unimers are observed � a behavior attributed to the inability of the PCHD blocks to pack. Polystyrene-block-poly(2-vinylpyrinde) (PS-PVP) star block copolymers also display unusual aggregation behavior that depends upon the number of arms arranged about the central core.  In toluene, which is selective for PVP, 26-arm and 40-arm PS-PVP stars are unable to aggregate due to their highly branched structure. However, 8-arm stars appear to be at a boundary, where they can remain as isolated chains in solution or aggregate into micellar structures. These studies stimulate thinking as to how novel structures may be engineered from simpler building blocks.

Self-assembly behavior of topologically-constrained block copolymers

247th National Meeting (2014)

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