Synthesis and Self-Assembly of Amphiphilic Macrocyclic Block Copolymer Topologies

We demonstrated the synthesis of miktoarm star block copolymers of AB, AB(2), and A(2)B, in which block A consisted of linear poly(tert-butyl acrylate) (P(t)BA) and block B consisted of cyclic polystyrene. These structures were produced using the atom transfer radical polymerization to make telechelic polymers that, after modification, were further coupled together by copper-catalyzed "click" reactions with high coupling efficiency. Deprotection of P(t)BA to poly(acrylic acid) (PAA) afforded amphiphilic miktoarm structures that when micellized in water gave vesicle morphologies when the block length of PAA was 21 units. Increasing the PAA block length to 46 units produced spherical core-shell micelles. AB(2) miktoarm stars packed more densely into the core compared to its linear counterpart (i.e., a four times greater aggregation number with approximately the same hydrodynamic diameter), resulting in the PAA arms being more compressed in the corona and extending into the water phase beyond its normal Gaussian chain conformation. These results show that the cyclic structure attached to an amphiphilic block has a significant influence on increasing the aggregation number through a greater packing density. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4603-4612, 2011