Influence of Architecture on the Behavior of Microphase Separated Block Copolymers.

摘要

The nanoscale self-assembly of block copolymers at the ∼10-100 nm length scale has exciting potential applications in next-generation nanolithography and nanotemplating, wherein the feature sizes are governed by the overall copolymer degree of polymerization, N. However, the thermodynamics of block copolymer microphase separation intrinsically limit the size of the smallest features accessible by this approach. This limitation stems from the fact that AB diblock copolymer self-assembly only occurs above a critical N that depends inversely on the magnitude of the effective interaction parameter Chi, which quantifies the energetic repulsions between the dissimilar monomer segments. In this dissertation, we first provide an overview of current routes to smaller periodicities in self-assembled block copolymers. While numerous reports have focused on developing "high Chi" AB diblocks that self-assemble at smaller values of N, the use of complex macromolecular architectures to stabilize ordered block copolymer nanostructures remains relatively unexplored. We report the melt-phase self-assembly behavior of block copolymer bottlebrushes derived from linking the block junctions of low molecular weight, symmetric poly(styrene-b-lactide) (PS-b-PLA) copolymers. These studies quantitatively demonstrate that increasing the bottlebrush backbone degree of polymerization (Nbackbone) reduces the critical PS-b-PLA copolymer arm degree of polymerization (Narm) required for self-assembly into lamellar mesophases by as much as 75%, thus reducing the nanoscale feature sizes accessible with this monomer chemistry. In studies of asymmetric block copolymer bottlebrushes, we observe a less significant reduction in the Narm required for self-assembly into a hexagonally-packed cylinders morphology. These results are rationalized in terms of how monomer concentration fluctuation effects manifest upon ordering a disordered copolymer into either a lamellar or cylindrical morphology.;Finally, the chemistry and physics of two other block copolymer systems are explored: (1) the self-assembly, thin film template fabrication, and post fabrication-template modification of reactive poly(styrene-b-vinyl dimethylazalactone) block copolymers, and (2) the synthesis and rheological characteristics of amphiphilic poly(vinyl alcohol)-based ABA triblock copolymer hydrogels.