Hierarchical organization in polymeric systems
Hierarchical assembly of materials has attracted significant interest, since it provides opportunities to fabricate novel materials. In this thesis, we investigated three different systems where polymer chains organize hierarchically.
First, a semicrystalline triblock copolymer, poly(L-lactic acid- b-ethylene oxide-b-L-lactic acid) (PLLA- b-PEO-b-PLLA), was prepared and the effect of the block-wise construction on the sequential crystallization was investigated by comparison to the corresponding homopolymer blend. In the resultant spherulitic morphology, the crystallization of PEO occurred within the framework established by the PLLA crystals. The preformed PLLA crystals biased the PEO chain orientation and the effect was more significant in the block copolymer system, where PEO chains were covalently anchored to PLLA.
Secondly, the influence of the microenvironment of multifunctional chains on their organization was studied. For this investigation, styrene-based linear polymers having two different pendant groups, a carboxylic acid and a neutral group, on every repeat unit were prepared. With alkyl (n-C 10H21-) groups as the neutral pendant, the linear macromolecules assembled into thermally reversible globular aggregates through non-covalent interaction with multifunctional tertiary amines. The aggregates had a structural hierarchy and remained stable without inter-particle crosslinking. In the absence of the alkyl pendant groups, control over the structure and properties of the aggregates was lost.
In a third system, the coupled self-assembly of bionanoparticles and block copolymers was investigated. A simple way to incorporate bionanoparticles into a thin film of water-insoluble block copolymer was developed by combining the bionanoparticle adsorption on a polymer film and subsequent annealing under solvent vapor. Through the use of a block copolymer having a positively charged component, the loading of bionanoparticles increased significantly. When highly loaded, a hierarchical co-assembly of the block copolymer and the bionanoparticle was observed where the microphase separation of the block copolymer forced a segregation of bionanoparticles to the grain boundaries, forming a much larger scale structure.
0794: Materials science