Polymeric betaines gain considerable attention for their interesting solution properties, but even more so, for their favorable bio- and haemocompatible properties. When incorporated into materials or used as surface coatings, some of these zwitterionic polymers strongly resist protein absorption due to their hygroscopic nature, making betaines promising candidates for medical diagnostics, drug delivery, and tissue engineering applications. This dissertation introduces novel norbornene-based polybetaines as foundational materials for biological applications, including non-fouling coatings and antimicrobial macromolecules. Sulfo- and carboxybetaines, composed of backbones that do not contain hydrolyzable units under physiological conditions, as well as new polymers that carry a dual functionality at the repeat unit level, coupling a zwitterionic functionality with an alkyl moiety varied to adjust the amphiphilicity of the overall system, are introduced. How structural changes, backbone chemistry, hydrophilicity/amphiphilicity, and coating surface roughness impact their non-fouling properties is investigated.

Co-continuous structures generated from the phase separation of polymer blends present many opportunities for practical application. Due to the large interfacial area in such structures and the incompatibility between the components, such non-equilibrium structures tend to coarsen spontaneously into larger sizes and eventually form dispersed morphologies. Here, we utilize various strategies to kinetically stabilize the co-continuous structures in polymer blend systems at nano- to micro- size scales. In the partially miscible blend of polystyrene and poly(vinyl methyl ether), we took advantage of the spinodal decomposition (SD) process upon thermal quenching, and arrested the co-continuous micro-structures by the addition of nanoparticles. In this approach, the critical factor for structural stabilization is that the nanoparticles are preferentially segregated into one phase of a polymer mixture undergoing SD and form a percolated network (colloidal gel) beyond a critical loading of nanoparticles. Once formed, this network prevents further structural coarsening and thus arrests the co-continuous structure with a characteristic length scale of several microns. Our findings indicate that a key to arresting the co-continuous blend morphology at modest volume fractions of preferentially-wetted particles is to have attractive, rather than repulsive, interactions between particles. For the immiscible blend of polystyrene and poly(2-vinyl pyridine) (PS/P2VP), we presented a strategy to compatibilize the blend by using random copolymers of styrene and 2-vinylpyridine, controlling the degree of immiscibility between PS and P2VP. Based on such compatibilization, co-continuous structured membranes, having characteristic size down to tens of nanometers, were fabricated in a facile way, via the solvent-induced macrophase separation of polymer blend thin films. The feature size was controlled by controlling the film thickness and varying the molecular weight of the PS homopolymer and the random copolymers. As the processing method (solution casting) is simple and the structures are insensitive to the solvent or substrate choices, this approach shows great potential in the large scale fabrication of co-continuous nanoscopic templates on flexible substrates via roll-to-roll processes. Moreover, we proposed a quasi-binary blend system based on the PS/P2VP pair with the addition of a common solvent. An experimentally accessible phase mixing temperature was achieved, and the co-continuous morphologies were generated via thermally induced spinodal decomposition. The addition of solid particles significantly slowed down the coarsening kinetics and, in some cases, arrested the co-continuous structures at ∼6 µm for a short period of time. This study suggests an alternative means to achieve co-continuous structures in polymer solutions and also provides better understanding of the thermodynamics and kinetics of polymer blend phase separation. Our research demonstrates several means of kinetically trapping the non-equilibrium interconnected structures at sub-micron to tens-of-nanometer size scales that are germane to several functions including active layers of photovoltaic cells and polymer-based membranes.

This thesis describes the synthesis and applications of a new series of amphiphilic homopolymers and copolymers consisting of hydrophobic polyolefin backbone and hydrophilic phosphorylcholine (PC) pendant groups. These polymers are synthesized by ring opening metathesis polymerization (ROMP) of a novel PC- cyclooctene monomer, and copolymerization of various functionalized cyclooctene comonomers. Incorporation of different comonomers into the PC-polyolefin backbone affords copolymers with different functionalities, including crosslinkers, fluorophores, and other reactive groups, that tune the range of applications of these polymers, and their hydrophobic/hydrophilic balance. The amphiphilic nature of PC-polyolefins was exploited in oil-water interfacial assembly, providing robust polymer capsules to encapsulate and deliver nanoparticles to damaged regions of a substrate in a project termed `repair-and-go.' In repair-and-go, a flexible microcapsule filled with a solution of nanoparticles probes an imperfection-riddled substrate as it rolls over the surface. The thin capsule wall allows the nanoparticles to escape the capsules and enter into the cracks, driven in part by favorable interactions between the nanoparticle ligands and the cracked surface (i.e., hydrophobic-hydrophobic interactions). The capsules then continue their transport along the surface, filling more cracks and depositing particles into them. The amphiphilic nature of PC-polyolefins was also exploited in aqueous assembly, forming novel polymer vesicles in water. PC-polyolefin vesicles ranged in size from 50 nm to 30 µm. The mechanical properties of PC-polyolefin vesicles were measured by micropipette aspiration techniques, and found to be more robust than conventional liposomes or polymersomes prepared from block copolymers. PC-polyolefin vesicles have potential use in drug delivery; it was found that the cancer drug doxorubicin could be encapsulated efficiently in PC-polyolefin vesicles. In another application, PC-polyolefins were used as antifouling coatings for ultrafiltration (UF) and reverse osmosis (RO) water purification membranes. These polymers were found to reduce surface fouling in both UF and RO membranes. Finally, PC-substituted ruthenium benzylidene catalysts were synthesized and evaluated for ROMP in water. PC-substituted catalysts proved effective towards productive metathesis of water soluble cyclic olefins including PEG-substituted oxanorbornene.

Nanostructured magnetic materials are important for various applications, and hence their development is critical for the advancement of science and technology. Coupling self-assembly to the generation of magnetic materials in a simple, straight-forward manner has remained a challenge. Here, a series of novel cobalt-functionalized block copolymers (BCPs) with various block ratios were synthesized using ring-opening metathesis polymerization (ROMP). These BCPs self-assembled into different nanostructured morphologies, including cylindrical, lamellar, and inverted cylindrical phases. Upon a simple heat treatment, all these nanostructured materials exhibited room temperature ferromagnetic (RTF) behavior due to the nanoconfinement of the cobalt species within one phase. The effect of dimensionality, or the degree of nanoconfinement, on the macroscopic magnetic properties was studied using superconducting quantum interference device (SQUID) magnetometer. The most highly constrained cylindrical morphology yielded the highest coercivity. The inverted cylindrical morphology, analogous to antidot materials, in which a 3D magnetic matrix is confined between diamagnetic cylinders, showed the second highest coercivity, while the least confined lamellar morphology exhibited the lowest coercivity value. A series of metal-containing block-random copolymers composed of an alkyl-functionalized homo block (C16) and a random block of cobalt complex- (Co) and ferrocene-functionalized (Fe) units was synthesized via ROMP. Taking advantage of the block-random architecture, the influence of dipolar interactions on the magnetic properties of these nanostructured BCPs was studied by varying the molar ratio of the Co units to the Fe units, while maintaining the cylindrical phase-separated morphology. DC magnetic measurements, including magnetization versus field, zero-field-cooled and field cooled, as well as AC susceptibility measurements, showed that the magnetic properties of the nanostructured BCPs could be easily tuned by diluting the cobalt density with Fe units in the cylindrical domains. Decreasing the cobalt density weakened the dipolar interactions of the cobalt nanoparticles, leading to the transition from a room temperature ferromagnetic to a superparamagnetic material. These results confirmed that dipolar interactions of the cobalt nanoparticles within the phase-separated domains were responsible for the RTF properties of the nanostructured BCPs. The effect of domain size on the magnetic properties of these RTF materials was investigated using a series of five cobalt-containing BCPs with various molecular weights and constant block ratios. The BCPs self-assembled into cylindrical morphologies with different domain sizes upon solvent annealing, and then were converted to RTF materials upon a simple heat treatment. The domain sizes of these RTF materials did not show a significant impact on their coercivity values, possibly because the domain size range investigated was not large enough and the cobalt-cobalt dipolar interactions were nearly constant throughout. At the same time, this study confirms that the RTF materials generated from these novel BCPs are robust. (Abstract shortened by UMI.)

Model glassy polymers, polymethyl methacrylate (PMMA) and polycarbonate (PC) are used to experimentally probe several aspects of polymer fracture. In Chapter 1, the method of pre-stress is employed as a means of improving the fracture properites of brittle PMMA. Samples are tested under equi-biaxial compression, simple shear and a combination of biaxial compression and shear. Equi-biaxial compression is shown to increase the threshold stress level for projectile penetration whereas shear pre-stress has a large effect on the overall energy absorbed during an impact. There is also an apparent interaction observed between compression and shear to dramatically increase the threshold stress. Pre-stressed laminates of PMMA and PC show an increase in damage area because of the unique formation of a secondary cone. In Chapter 2, the effect of stress state on stress relaxation in PMMA and PC is investigated. Direct comparisons are made between uniaxial and biaxial loading conditions. The experimental methods used highlight the effect of hydrostatic stress on the relaxation process. The data shows an increase in relaxation time and increase in the breadth of the relaxation spectrum with increases in hydrostatic stress. This suggests that the stress state can have a significant effect on the useful lifetime of pre-stressed articles. In Chapter 3, Mode I and II fracture studies are performed from quasi-static to low velocity impact rates on PMMA and PC. Mode II testing utilizes an angled double-edge notched specimen loaded in compression. The shear banding response of PMMA is shown to be highly sensitive to rate, with diffuse shear bands forming at low rates and sharp distinct shear bands forming at high rates. As the rate increases, shear deformation becomes more localized to the point where Mode II fracture occurs. PC is much less rate dependent and stable shear band propagation is observed over the range of rates studied with lesser amounts of localization. A new theory is formulated relating orientation in a shear band to intrinsic material properties obtained from true-stress true-strain tests. In a qualitative sense the theory predicts the high rate sensitivity of PMMA. A kinematic limit for orientation within a shear band is also derived based on entanglement network parameters. Mode II fracture in PMMA is shown to occur at this kinematic limit. For the case of PC, the maximum impact rates were not high enough to reach the kinematic limit. In Chapter 4, the deformation response, as observed in a shear band is interpreted through the characterization of the "intrinsic material properties" obtained from true stress—true strain 8compression tests. The relatively high rate sensitivity of PMMA deformed at room temperature is related to the proximity of the beta transition to the test temperature. This is also shown in corollary experiments on PC where deformation near the beta transition is accompanied by an increase in rate sensitivity. Physical aging results in a more narrow alpha transition and is shown to increase strain localization and decrease rate sensitivity at low strain rates.

This thesis explores the effects of bilayer mechanics on the adhesion of biomimetic membranes and vesicles, establishing copolymer lamellae as versatile model membranes that more widely vary membrane mechanics and chemical functionalization than can be achieved using phospholipids. This new biomimetic system provides fundamental insight into cell adhesion, and motivates new design strategies for vesicles in applications such as targeted delivery.^ This study focused on the dynamic adhesion kinetics and spreading of vesicle pairs held in micropipettes at moderate tensions. The program employed two copolymers of different membrane stiffnesses, a graft copolymer of poly(dimethyl siloxane)-poly(ethylene oxide) [PDMS-PEO] and a diblock copolymer of poly(butadiene)-PEO [PBD-PEO]. The depletion-driven adhesion between pairs of these vesicles was studied, as was the avidin-biotin-driven adhesion between functionalized vesicles. This experimental grid therefore varied the membrane stiffness, adhesion strength, and point-wise versus laterally uniform application of adhesive forces.^ This study systematically demonstrated, for the first time, the activated nature of vesicle adhesion and spreading, with the bending cost of kink formation at the spreading front comprising a line tension that destabilizes adhesion nuclei. Despite modest differences between the bending moduli of phospholipid and stiffer copolymer vesicles, the effect was often sufficiently strong to prevent spreading, or at least produce a lag time prior to the onset of spreading. For instance, flexible membranes subject to depletion forces as small as 0.008 erg/cm2 responded instantaneous to changes in membrane tension, achieving the equilibrium contact angle in less than a second. Stiff vesicles, however, never spread over a substrate vesicle or displayed an equilibrium contact angle, even when depletion forces were increased to 0.35 erg/cm 2. Avidin-biotin functionalized flexible vesicles displayed a lag time prior to spreading while fully functionalized stiff vesicles never spread over substrate vesicles. Of note, in cases where spreading did not, or had not yet occurred, there was evidence for adhesion in a contact nucleus. For instance, avidin-biotin functionalized vesicles could not be separated, and unfunctionalized vesicles subject to depletion forces deformed momentarily upon separation.^ Estimates of the activation energy associated with spreading for depletion-driven adhesion were consistent with experimental observations, while a semi-quantitative treatment of avidin-biotin binding kinetics predicted the form of the concentration-dependence of the pre-spreading lag time. Once initiated, spreading kinetics were rapid and independent of membrane tension.^ These results find significance in the areas of fundamental membrane physics and in biology. As micropipette manipulation is becoming an increasingly popular tool for membrane characterization, the current thesis demonstrates that the approach to equilibrium, as measured through the contact angle, may be impeded by bending mechanics, rendering the Young's analysis of adhesion strength meaningless. The findings also suggest that in cell adhesion and processes involving sharp membrane curvature, such as endocytosis, membrane mechanics likely plays an important role in the dynamic mechanism.^

This thesis focuses on the manipulation of polymers and composites on length scales ranging from the nanoscopic to microscopic. In particular, on the microscopic length scale electric fields were used to produce instabilities at the air surface and at polymer interfaces that lead to novel three dimensional structures and patterns. On the nanoscopic length scale, the interaction of ligands attached to nanoparticles and polymer matrix were used to induce self-assembly processes that, in turn, lead to systems that self-heal, self-corral, or are patterned. For manipulation at the micron length scale, electrohydrodynamic instabilities were used in trilayer system composed of a layer of poly(methyl methacrylate) (PMMA), a second layer of polystyrene (PS) and a third layer of air. Dewetting of the polymer at the substrate at the polymer/polymer interface under an applied electric field was used to generate novel three dimensional structures. Also, electrohydrodynamic instabilities were used to pattern thin polymer films in conjunction with ultrasonic vibrations and patterned upper electrodes. Self-assembly processes involving polymers and nanoparticles offer a unique means of generating pattern materials or materials that self heal. Simple polymer/nanoparticle composites were investigated. Here, in the absence of interactions between the poly(ethylene oxide) ligands attached to the nanoparticles and PMMA polymer matrix, the opportunity to generate self-healing systems was opened. The size of the nanoparticle was varied and the effect on diffusion of nanoparticle in the polymer matrix was studied. CdSe nanorods were also assembled on a substrate templated with or guided by microphase separated diblock copolymers. The nanorods were incorporated in the diblock copolymer thin films by spin coating the co-solution of nanorods and polymer, surface adsorption of nanorods on to the patterned diblock copolymer films and surface reconstruction of PS/PMMA diblock copolymer thin film. Further, the interactions between the PMMA polymer matrix and the tri n-octyl phosphine oxide ligands attached to an anisotropic nanoparticle, i.e. nanorods, were used to influence the dispersion of the nanorods in the polymer. This led to a novel assembly, termed self-corralling where under an applied electric field highly oriented, highly ordered arrays of nanorods form. Further, self corralling of nanorods was directed by chemically patterned substrates.

Room temperature ionic liquids (ILs) are a unique class of solvents which are characterized by non-volatility, non-flammability, electrochemical stability and high ionic conductivity. These properties are highly desirable for ion-conducting electrolytes, and much work has focused on realizing their application in practical devices. In addition, hydrophilic and ionophilic polymers are generally miscible with ILs. The miscibility of ILs with ion-coordinating polymers makes ILs effective plasticizers for gel polymer electrolytes. Due to their unique properties, ILs present a means to realize the next generation of energy storage technology. In this dissertation, the fundamental interactions between poly(ethylene oxide) (PEO) and a variety of room temperature ILs were investigated. ILs with acidic protons were demonstrated to form a stronger interaction with PEO than ILs without such protons, suggesting that hydrogen bonding plays a dominant role for PEO miscibility with ILs. The hydrogen bonding interaction is selective for the PEO block of a PEO-b-PPO-b-PEO block copolymer (BCP). Therefore, blending these copolymers with the strongly interacting IL 1-butyl-3-methylimidazolium hexafluorophosphate ([BMI][PF6]) induced microphase separation into a well-ordered structure, whereas the neat copolymer is phase mixed. At sufficient quantities, the interaction between [BMI][PF6] and PEO suppresses PEO crystallinity entirely. In addition, the induced microphase separation may prove beneficial for ion conduction. Therefore, microphase separated copolymer/IL blends were investigated as potential gel polymer electrolytes. Cross-linkable block copolymers which microphase separate when blended with [BMI][PF6] were synthesized by modifying PPO-b-PEO-b-PPO copolymers with methacrylate end-groups. Cross-linking these copolymers while swollen with an IL generates ion gels with high ionic conductivities. The copolymer/IL blends vary from a well-ordered, strongly microphase separated state to a poorly ordered and weakly microphase separated state, depending upon the molecular weight. Stronger microphase separation results in higher mechanical strength upon cross-linking. However, this does not greatly affect ion conductivity. Nor is conductivity affected by forming gels from cross-linked PEO homopolymers when compared to BCPs. It was found that BCPs can be beneficial in producing gel electrolytes by allowing sequestration of phase selective cross-linkers away from the conducting block. Cross-linker molecules that are selective for the PPO blocks can be used to increase the mechanical strength of the gels with only a small effect on the conductivity. When cross-linkers that partition to the mixed PEO/IL block are used, the conductivity decreases by nearly a factor of 2. These studies show how ILs interact with PEO and how gel polymer electrolytes can be constructed with the IL [BMI][PF6]. While BCPs cannot directly be used to increase ion conductivity, they do allow for greater mechanical strength without sacrificing conductivity. This suggests many new approaches that may be used to simultaneously achieve high ionic conductivity and mechanical strength in solid and gel polymer electrolytes.

This thesis is divided into two research initiatives: The fabrication and study of bulk, co-continuous, cellulosic-polymer composites with the aid of supercritical CO2 (SC CO2); and the study of poly(vinyl alcohol) (PVOH) modification and surface activity in ionic liquids. The first part of this thesis utilizes the tunable solubility, gas-like diffusivity, and omniphilic wettability of SC CO2 to incorporate and subsequently polymerize silicone and poly(enemer) prepolymer mixtures throughout various cellulosic substrates. Chapters two and three investigate the mechanical properties of these composites and demonstrate that nearly every resulting composite demonstrates an improved flexural modulus and energy release rate upon splitting. Fire resistance of these composites was also investigated and indicates that the heat release rate, total heat released, and char yield were significantly improved upon for all silicone composites compared to the untreated cellulosic material. Chapter four looks specifically at aspen-silicone composites for thermo-oxidative studies under applied loads in order to study the effect of silicone incorporation on the failure kinetics of aspen. The aspen-silicone composites tested under these conditions demonstrated significantly longer lifetimes under the same loading and heating conditions compared with untreated aspen. The second part of this thesis focuses on studying ionic liquids as potentially useful solvents and reaction media for poly(vinyl alcohol). Two ionic liquids (1-Butyl-3-methylimidizolium chloride and tributylethylphosphonium diethylphosphate) were found to readily dissolve PVOH. More importantly, we have demonstrated that these solvents can be used as inert reaction media for PVOH modification. Both ionic liquids were found to facilitate the quantitative esterification of PVOH, while only the phosphonium ionic liquid supports the quantitative urethanation of the polymer. In an attempt to tune the surface properties of ionic liquid/polymer solutions, PVOH was also partially esterified with low surface energy substituents. Both surface tension and surface composition of the ionic liquid/polymer solutions can be manipulated by the stoichiometric addition of low surface energy acid chlorides. This work on the modification of PVOH can be directly applied to the modification of polysaccharides such as cellulose which could have important implications from a sustainability and energy standpoint.

A series of para-linked aromatic polyamides synthesized with the aim of making optically uniaxial, transparent films and fibers for optical applications, are found to have anomalous properties. Stretched films of these polyamides are highly birefringent and non-crystalline at the same time. These rod-like polyamides do not form lyotropic solutions and are soluble in common solvents like THF, unlike other rod-like polymers. With the goal of understanding this behavior from a molecular standpoint we have quantitatively characterized the geometric, optical and hydrodynamic properties of one of these polyamides. With angle light scattering measurements on polyamide in THF were used in conjunction with electric birefringence measurements to determine the weight average molecular weight, M$\sb{\rm w}$, the root mean square z-averaged radius of gyration, R$\sb{\rm gz}$, the apparent second virial coefficient, A$\sb{\rm 2app}$ and the monomer molecular anisotropy ratio $\varepsilon$. The polydispersity correction was applied theoretically by assuming the most probable distribution. Hydrodynamic and optical properties were determined with viscometry and differential refractometry respectively. The aromatic polyamide studied can be satisfactorily modeled as a Kratky-Porod wormlike chain with a persistence length of 220 $\pm$ 50 A and a monomer optical anisotropy ratio of 2.3 $\pm$ 0.3. The excluded volume effect is found to be negligible in THF at 25$\sp\circ$C. The small axial ratio of 30 may be partly responsible for the non-lyotropic behavior. The refractive index of 1.67 is in good agreement with that of similar polyamides. The repeat unit has a high optical anisotropy leading to highly birefringent films. It is also conclusively established that there is no aggregation due to H-bonding in the absence of moisture. The light scattering theory of Nagai and the hydrodynamic theory adopted for semiflexible chains is found to hold very well for the polyamide studied. Based on the agreement between experiment and theory we infer that the molecular weight distribution is of the most probable type. Our depolarized light scattering data indicate that the straight line behavior observed in Zimm plots even for $\rm R\sb{g}\sp2q\sp2>1$, upto $\rm R\sb{g}\sp2q\sp2$ of 3.5 is due to the combined effect of polydispersity, large size and optical anisotropy of the molecule.