In an effort to synthesize macromolecules comprising both covalent and non-covalent bonding to tune ultimate physical properties, a variety of methodologies and functionalization strategies were employed. First, protected functional initiation, namely 3-[(N-benzyl-N-methyl)amino]-1-propyllithium and 3-(t-butyldimethylsilyloxy)-1-propyllithium, in living anionic polymerization of isoprene was used to yield well-defined chain end functional macromolecules. Using both initiating systems, polymers with good molar mass control and narrow molar mass distributions were obtained and well-defined chain end functionality was observed. There was no observed effect on the polymer microstructure from the polar functionality in the initiator, with ~92% 1,4- and 8% 3,4-enchainment observed in each case. Further investigation of the 3-[(N-benzyl-N-methyl)amino]-1-propyllithium initiated polyisoprenes proved that facile deprotection was not possible and residual catalyst was not removable from the polymer. However, polymers initiated with 3-(t-butyldimethylsilyloxy)-1-propyllithium were quantitatively hydrogenated and deprotected under relatively mild conditions to yield hydroxyl functional macromolecules in several architectures, including linear and star-shaped. Excellent conversion from arm polymer to star polymer was observed and well-defined macromolecules were obtained. Subsequently, a series of non-functional, hydroxyl functional, and 2-ureido-4[1H]-pyrimidone (UPy) chain end functional linear and star-shaped poly(ethylene-co-propylene)s were synthesized and characterized. The melt phase properties were investigated using melt rheology and the effect of macromolecular topology and multiple hydrogen bond functionality was investigated. Linear UPy functional poly(ethylene-co-propylene)s exhibited increased viscosity and shear thinning onset at lower frequencies than non-functional polymers of similar molar mass due to interaction of the multiple hydrogen bonding groups. Star-shaped UPy functional poly(ethylene-co-propylene)s showed inhibition to terminal flow and the absence of a zero shear viscosity in melt rheological characterization, indicative of a network like structure imparted from the multiple hydrogen bonding interactions. In addition, the living anionic polymerization of D3 was controlled using the functionalized initiators3-[(N-benzyl-N-methyl)amino]-1-propyllithium and 3-(t-butyldimethylsilyloxy)-1-propyllithium. Good molar mass control and narrow molar mass distributions were observed. In contrast to the polyisoprene homopolymers, facile deprotection of the 3-(t-butyldimethylsilyloxy)-1-propyllithium was not possible due to the acid sensitivity of the poly(dimethylsiloxane) backbone. However, facile deprotection of the protected secondary amine was achieved through hydrogenolysis and well-defined terminal amine functionalized poly(dimethylsiloxane) was synthesized, which are then amenable to further functionalization reactions. In contrast to the well-defined polymers synthesized using living anionic polymerization, free radical polymerizations was used to synthesize free radical copolymers with broader polydispersities and pendant UPy groups. These copolymers were compared with a simple dimeric hydrogen bonding carboxylic acid containing copolymer. Melt rheological characterization revealed that, at similar concentrations, the effect of the UPy group was much greater than the carboxylic acid, and broadened plateau moduli and increased viscosity for the UPy containing polymers were observed, while the acid containing polymer exhibited similar results to a non-functional control. The dynamic viscosity was observed to increase systematically with increasing UPyMA incorporation and the quadruple hydrogen bonding interactions were observed to dissociate between ~80-150 °C. / Ph. D.

The implications of chain topology and intermolecular interactions on the electrospinning process were investigated for linear and randomly branched polymers. Empirical correlations were developed based on solution rheological measurements that predict the onset of electrospun fiber formation and average fiber diameter. In particular, for neutral, non-associating polymer solutions, the minimum concentration required for fiber formation was the entanglement concentration (Ce), and uniform, bead-free fibers were formed at 2 to 2.5 Ce. This was attributed to entanglement couplings stabilizing the electrospinning jet and preventing the Raleigh instability. Moreover, the influence of molar mass and degree of branching on electrospun fiber diameter was eliminated when the polymer concentration was normalized with Ce, and the fiber diameter universally scaled with C/Ce to the 2.7 power. Polymers modified with quadruple hydrogen bonding groups were investigated to determine the role of intermolecular interactions on the solution rheological behavior and the electrospinning process. In nonpolar solvents, the hydrogen bonding functionalized polymers displayed significant deviation from the electrospinning behavior for neutral solutions due to the strong intermolecular associations of the multiple hydrogen bonding groups. The predicted electrospinning behavior was recovered when the hydrogen bonding interactions were screened with a polar solvent. Moreover, it was observed that branching and multiple hydrogen bonding afforded significant processing advantages compared to functionalized, linear analogs of equal molar mass. For example, branched chains in the unassociated state possessed a larger Ce compared to the linear chains, which indicated a lower entanglement density of the former. However, in the associated state the linear and branched chains possessed nearly equivalent Ce values, suggesting a similar entanglement density. Thus, the branched polymers displayed significantly lower viscosities in the unassociated state compared to linear polymers, while still retaining sufficient entanglements in the associated state due to the reversible network structure of the multiple hydrogen bond sites. The solution rheological and processing behavior of polyelectrolyte solutions was also investigated to discern the role of electrostatic interactions on electrospun fiber formation. In particular, the polyelectrolyte solutions formed nano-scale electrospun fibers with an average fiber diameter 2 to 3 orders of magnitude smaller than neutral polymer solutions of equivalent viscosity and C/Ce. This was attributed to the very high electrical conductivity of the polyelectrolyte solutions, which imparted a high degree of charge repulsion in the electrospinning jet and increased the extent of plastic stretching in the polymer filament. In fact, the average diameter of the polyelectrolyte fibers under certain conditions was less than 100 nm, which makes them good candidates for protective clothing applications due to their high specific surface area. Moreover, the neutral polymer solution electrospinning behavior was recovered after the addition of NaCl, which screened the electrostatic charge repulsions along the polyelectrolyte main chain. Finally, electrospun, biocompatible phospholipid membranes were produced from solutions of entangled worm-like lecithin micelles. This is the first example of successfully electrospinning low molar mass, amphiphilic compounds into uniform fibers. Electrospinning the phospholipid worm-like micelles into nonwoven fibrous mats will afford direct engineering of bio-functional, high surface area membranes without the use of multiple synthetic steps, complicated electrospinning setups, or post processing surface treatments. / Ph. D.

The synthesis of a variety of novel functionalized polymers using living polymerization techniques to achieve functional and stimuli responsive coatings on silica surfaces are described. Since microscopic features on a surface influence the overall wetting properties of the surface, a systematic investigation of the influence of polymer architecture on the microscopic characteristics of the modified surfaces was studied using silane-functionalized linear and novel star-branched polystyrene (PS). Star-branched modifiers provide functional and relatively well-defined model systems for probing surface properties compared to ill-defined highly branched systems and synthetically challenging dendrimers. Using these simple star-shaped macromolecules it was shown that the topographies of the polymer-modified surfaces were indeed influenced by the polymer architecture. A model explaining the observed surface features was proposed. A living polymerization strategy was also used to synthesize centrally functionalized amphiphilic triblock copolymers. The amphiphilic copolymers exhibited stimuli responsive changes in surface hydrophobicity. In spite of multiple solvent exposures, the copolymer films remained stable on the surface indicating that the observed changes in surface properties were due to selective solvent induced reversible rearrangement of the copolymer blocks. The chemical composition of the copolymers was tailored in order to tune the response time of the surface anchored polymer chains. Thus, the polymer coatings were used to reversibly change the surface polarities in an on-demand fashion and could find possible applications as smart adhesives, sensors and reusable membrane devices. In contrast to the afore-mentioned covalent modification approach, which often leads to permanent modification of surfaces, renewable surfaces exhibiting "universal" adhesion properties were also obtained through non-covalent modification. By employing hydrogen bonding interactions between DNA bases, surfaces functionalized with adenine groups were found to reversibly associate with thymine-functionalized polymers. This study describing the solvato-reversible polymer coating was the first demonstration on silica surfaces. A systematic investigation of the influence of surface concentration of the multiple hydrogen bonding groups and their structure on the extent of polymer recognition by the modified surfaces is also discussed. / Ph. D.

The ring opening polymerization of D,L-lactide (DLLA) using multifunctional hydroxyl-terminated initiators and catalyst/coinitiator systems based on Sn(Oct)2 afforded the preparation of star-shaped, poly(D,L-lactide)s (PDLLA)s of controlled molar mass, narrow molar mass distributions, and well-defined chain end functionality. Various modifications of star-shaped PDLLA resulted in macromolecules with tailored functionalities for biomedical applications. Star-shaped PDLLAs were modified to contain photoreactive methacrylate end groups and subsequent photo-crosslinking was performed. Photo-crosslinked networks based on methacrylated star-shaped PDLLAs exhibited thermal properties and mechanical performance that were superior to current approved clinical adhesives. In addition, the thermal and mechanical properties of the networks were strongly dependent on the composition and molar mass of the star-shaped PDLLA precursors. Tensile strengths in the range of 8-21 MPa were obtained while the Young's modulus increased from 12 to 354 MPa and were higher for networks based on urethane containing polymers. Star-shaped PDLLAs bearing complementary adenine and thymine terminal units were also prepared. The hydrogen bonding associations between complementary PDLLA macromolecules depended strongly on molar mass and hence, the concentration of multiple hydrogen bonding units. 1H NMR spectroscopy confirmed the formation of hydrogen-bonded complexes with a 1:1 optimal stoichiometry and an association constant of 84 M-1. The hydrogen-bonded complexes also exhibited significantly higher solution viscosities than non-blended polymer solutions of similar molar mass and concentration. Thermoreversible associations of PDLLA-based complementary polymers were observed in the melt phase and the melt viscosity of a blended complex was consistently an order of magnitude higher than non-functionalized star-shaped PDLLA of similar molar mass. Furthermore, melt electrospinning of the hydrogen-bonded complexes successfully resulted in fibers of significantly larger diameter (9.8 ± 2.0 µm) compared to the individual precursors (PDLLA-A = 4.0 ± 0.6 µm and PDLLA-T = 4.4 ± 1.0 µm). These results suggested that thermoreversibility, as well as the strength of the hydrogen bonding interactions between the end groups of the tailored star-shaped PDLLA-based supramolecular polymers controlled the fiber diameter in the melt electrospinning process. Highly ordered microporous honeycomb structures were developed on photo-functional star-shaped PDLLA surfaces. The pore dimensions were dependent on polymer solution concentration, polymer molar mass and relative humidity. The combination of self-organizing and cross-linking techniques resulted in free-standing, PDLLA membranes with high chemical stability as well as higher mechanical strength for further material patterning. Amikacin, an antibiotic commonly used for treating infections was successfully encapsulated in star-shaped PDLLA fibers that were electrospun from solution. Preliminary results suggested that molecular architecture influenced the encapsulation of the antibiotic and subsequent drug release profile. / Ph. D.