Investigating Random Heteropolymers. Synthesis, Characterization, and Applications

This dissertation focuses on the development of polymeric materials incorporating chemical heterogeneity and statistical randomness as design parameters. Random heteropolymers have a rich history within the synthetic and natural communities, for both the inherent fundamental science insights they can provide, and their utility within applications. These materials encompass a near limitless design space if one considers the comonomer selection, relative comonomer composition, comonomer sequence, stereochemistry, degree of polymerization, and end group functionality. While exact simultaneous control over every facet of this list simultaneously is not currently possible for most systems, especially at scale, the advancements within the field of polymer chemistry have afforded us the opportunity to access a significant amount of the material space. Here, we utilize reversible addition-fragmentation chain transfer polymerization to produce random heteropolymers with diverse architectures and compositions. This provides both insight into the role of chemical diversity in polymeric materials, and promising directions for their use in functional applications./nA novel set of coil-comb block copolymers were designed, synthesized, and studied for their ability to microphase separate and incorporate nanoparticles for the production of hierarchically ordered nanocomposites. The coil block was formed using random co- and terpolymer blocks consisting of a balance of methyl- and lauryl-, and in some cases also oligo(ethylene glycol)-, side chains. The random sequence and comonomer selection enabled compositional balancing of the enthalpic interactions of the lauryl groups with the alkyl ligand passivated nanoparticles while ensuring sufficient conformational entropy to accommodate self-assembly. As a function of the random copolymer volume fraction, lamellar, cylindrical, and mixed morphologies were obtained, with well-ordered nanocomposites forming upon incorporation of the nanoparticles. Asymmetry in the phase diagram driven by the random coil block was observed. This study showcases the utility of random copolymers in the generation of polymer-nanoparticle composites./nMost traditional polymer characterization techniques provide ensemble measurements of the material properties. Sequence level characterization may provide key information on structure-function relationships and aid in the design of functional materials, yet techniques to do so for synthetic polymers, especially polyolefins, are currently unavailable. A software package titled ‘Compositional Drift’ was developed to provide in-silico sequence information for polymers synthesized via controlled radical techniques. This in turn enabled the ability to easily design controlled composition gradients and develop insight into sequences and characteristic monomer run length distributions for random heteropolymers./nMetal-binding random heteropolymer libraries were generated via post-modification of styrene-maleic anhydride copolymers in a combinatorial approach. Ligands choice was guided by protein metal binding site analysis. Chemical heterogeneity was found to improve processability and performance, and judiciously designed composition gradients enabled one-pot synthesis of functional materials. The materials displayed high binding capacity, metal dependent color change, and facile regenerability as a function of pH. Finally, four monomer random heteropolymers containing methyl-, oligo(ethylene glycol) methyl ether- 2-ethylhexyl-, and 3-sulfopropyl methacrylate were designed and studied for their ability to behave as protein-mimetic materials. The surfaces of proteins were found to be chemically heterogeneous with characteristic patch sizes in the 1-2nm range. The analysis of primary structure of proteins revealed similar chemical heterogeneity. Analysis of in-silico derived random heteropolymer sequences demonstrated statistically similar run length distributions across the ensemble. On the single chain level, sequences could be broken into segments of various length, characterized as hydrophilic, lipophilic, and amphiphilic based on the calculated cumulative hydrophobic-lipophilic balance of the comonomers contained within. This insight was used to develop two functional applications. Random heteropolymers were shown to perform as synthetic chaperones, similar to intrinsically disordered proteins, reproducibly providing chemical and thermal stabilization to a broad range of proteins in organic solvents and within materials. This stabilization was driven by the matching of the chemically diverse surface patches of the protein with the favorable non-covalent interactions afforded by the comonomer side chains. The polymers were also shown to enable selective proton transport across lipid bilayers at rates comparable to natural transmembrane proton channels. Overall lipophilic segments that contain oligo(ethylene glycol) side chains were found to insert into the lipid region, thereby anchoring the hydrophilic monomer facilitating the formation of hydrogen bonded water chains. Performance was experimentally assessed through systematic variance of monomer composition.

Advisor: Xu, Ting