Solution and Surface Properties of Architecturally- and Compositionally-Complex Block Copolymers and their Binary Mixtures

The spontaneous generation of complex structures from polymeric building blocks provides a simple yet effective route to create useful soft matter structures having potential application in a variety of nanotechnologies. The topology, chemical structure, block composition, and sequence of the constituent building blocks of polymers are tunable through synthetic chemistry. This tunability offers attractive opportunities to generate complex, yet well-defined structures with control over the geometry, packing symmetry, and microdomain structure. This thesis work involves the study of the self-assembly behaviors of architecturally complex amphiphilic block copolymers (ABCs). ABCs are composed of two or more chemically distinct blocks that are covalently bonded together. Because of the thermodynamic incompatibility between the blocks, they self-organize through microphase separation. Systems studied include multiblock linear copolymers, star-like copolymers and graft copolymers.

The self-assembly behaviors of polystyrene-poly(2-vinylpyridine) (PS-PVP) block copolymers have been systematically investigated in solution and in thin films. Binary mixtures containing linear diblock and triblock copolymers of different block lengths and star block copolymers having different numbers of constituent arms and composition were also investigated. In general, the ensembles that consist of monomodal PS-PVP block copolymers exhibit simple nanoparticle-like structures. In contrast, binary mixtures of PS-PVP block copolymers with different component architectures produce a wider variety of micellar aggregates, including particle-like, worm-like and hierarchical structures, owing to the complex architecture-induced diversity of microphase segregation behaviors in the mixed systems.

In addition to studies of copolymer mixtures, the links between sequence, and composition on the self-assembly properties of a series of PLA-PEG containing bottlebrush copolymers were investigated in solution. It is found that the composition and sequence of the side-chains dictated the stability, thermodynamics, and size of micelle formation.

These studies clarify the self-assembly properties of ABCs and provide new insights into how micellar structures can be controlled by tuning macromolecular architecture, sequence, and polymer composition, as well as, in the case of mixtures, blend ratio. This work is expected to be valuable for understanding the self-assembly of complex copolymeric systems, which may find use in a variety of applications ranging from personalized medicine to environmental remediation, and lays the groundwork for self-assembly processing.