Seminars
Biological and Synthetic Methods for the Formation of Polymeric Nanostructures
Kevin Hermanson
Technical University of Munich
When: Monday, March 6, 2006
Time: 4:00 - 5:00 p.m.
Where: Sewall Hall Room 309
Abstract:
Many advanced biological and electronic materials rely on the formation of polymeric structures with controlled architectures. The formation of such structured materials can be accomplished by either directing a polymerization with template or through the assembly of preformed polymer chains. In the research presented here, concepts from colloid and polymer science are utilized to understand and assemble molecules into large structures using two different novel approaches. In the first approach bioactive thin shelled vesicles are formed from recombinant polypeptides through the templating of emulsion droplets. In the second approach controlled living polymerizations are conducted within a surfactant template to form polymeric structures of nanometer size length scales and well defined molecular weights.
Among the large variety of structures useful for implant devices and encapsulation technologies, one of the most ecumenical is that of the thin shelled vesicle. Such thin shelled vesicles can be formed from a large number of different colloids through the self-assembly of colloidal particles at the interface of emulsion droplets. Here this technique is combined with the natural propensity of silk proteins to associate and bind. In this process recombinant polypeptides that mimic the structure of spider silk are adsorbed on the interface of an emulsion droplet. Once the colloids are adsorbed, the emulsion interface induces the natural binding behavior of the silk mimetic polymers causing the molecules to bind together. The resulting structures are micron-sized vesicles with a shell thickness between 5 and 40 nanometers. The microstructural and mechanical properties of the final shell resemble the natural properties of natural spider silk, and as a result the assembled shells can be used to gain further insight into the structure-property relationship of silk.
In recent years, controlled living radical polymerization has become an important technique for the formation of polymers with controlled architecture and molecular weight. One of the more important techniques for controlled free radical polymerizations is that of reversible addition fragmentation transfer polymerization (RAFT). Using a RAFT agent, n-hexyl methacrylate was successfully polymerized in a microemulsion forming a polymer of low polydispersity and controlled molecular weight. Kinetic measurements combined with the molecular weight analysis confirm that the polymerization proceeded by a controlled living mechanism. Subsequent analysis of the polymerization mechanism through modeling demonstrates the limitations of this approach.
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