Structure-property behavior of free radical synthesized polydimethylsiloxane (PDMS) - polystyrene and PDMS-styrene derivative block polymers have been studied. The block polymers were provided by Dr. J. V. Crivello from GE. Two different types of segmented polytetramethyleneoxide (PTMO) based ionene elastomers were also investigated. The PTMO-dihalide ionenes were obtained through the courtesy of Dr. C. M. Leir in 3M, while the PTMO-dipyridinium ionenes were synthesized by Dr. B. Lee in Prof. McGrath’s research group at VPI&SU. In the free radical synthesized PDMS-PS block polymers, the molecular weight (MW) and the molecular weight distribution (MWD) of the PS blocks varied with the PDMS block length (block MW) comprising the macroinitiators, and the styrene conversion level. As the PDMS block length or the conversion level increased, the average PS block MW increased, and the molecular weight distribution of the PS block became broader. Multi-modal molecular weight distribution of the PS blocks was observed on the high conversion polymers with large PDMS blocks. As the MW and the MWD of the PS blocks changed, the morphology, the degree of phase mixing, and bulk properties of these PDMS-PS block polymers were altered as expected. At constant conversion level, the morphology of these block polymers changed from spherical PS domains in the PDMS matrix to a lamellar structure as the PDMS block length increased. As expected, their mechanical properties were also changed as morphology varied. At constant PDMS content, the systems with shorter PDMS blocks displayed elastomeric properties, while the polymers having large PDMS blocks behaved like a plastic due to a continuous lamellar morphology. The degree of phase mixing also decreased with an increase of the PS block length because of the increased incompatibility between the two block components. For a constant PDMS block length, the PS block length increased and the MWD of the PS blocks became broader when the styrene conversion level increased. Consequently, the morphology, the degree of phase mixing as well as the bulk properties of the block polymer also varied with conversion level. Addressing the segmented PTMO based ionene elastomers, these materials displayed excellent elastomeric properties which result from the ion clustering or ionic domain formation in a continuous PTMO matrix. The morphology and bulk properties of these ionene systems were strongly dependent on the strength of ionic association. By varying the ion content, the type of counter ion, or hard segment, the ionic association was changed. Therefore, the morphology and the bulk properties were also altered. Morphological textures of these ionene systems were studied by Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS). Due to the strong ion clustering, an ionene rod-like morphology was observed in the PTMO-dihalide ionene elastomers by both TEM and SAXS at low volume fraction of ionene content (<7 vol%). It is the first time that these two analytical methods have distinctly led to the same end result for any ionomer system! This morphological structure is not predicted by any of existing theories of ion clustering in ionomers nor the classical theories of block/segmented polymers. Finally, the morphology of these ionene systems was altered with ion content. When the ion content was decreased by increasing the PTMO segment length, the long-range ordered structure disappeared as well as the rod-like microphase structure. A very unique phenomenon, a highly reversible modulus "jump" with increasing temperature, has been observed for these ionene materials which has not been reported before. This "jump" is directly related to the ion content, type of counter ion and the hard segment. Based on experimental evidence, the "jump" is tentatively speculated to be caused by a conformational change in the ionene hard segments. However, further investigations are needed to support or disprove this speculation. / Ph. D.

The incorporation of substituted stilbenes in copolymers affects the resulting solution properties and their controlled radical polymerizations. Substituted stilbene monomers readily polymerize in an alternating fashion with acceptor comonomers such as maleic anhydride and maleimide. These sterically crowded polymer backbones are classified as semi-rigid. As this is an uncommon category of polymer backbone rigidity, examples of semi-rigid and rigid polyzwitterions in the literature were reviewed as well as stilbene-containing semi-rigid polymers. Using a deprotection strategy, anionic polyelectrolytes and polyampholytes of stilbene-maleic anhydride copolymers were synthesized and characterized by first synthesizing organic-soluble polymer precursors. Solution shear rheology and statistical segment length measurements reveal that carboxylated polyanions containing stilbene and maleic acid remain semi-rigid in aqueous solutions. It was found that these semi-rigid polyanions exhibited excellent anti-HIV activity possibly due to their more extended polymer chains. This was the first time that intrinsic polymer rigidity was introduced as a possible design parameter for microbicidal applications. Reversible addition fragmentation chain transfer (RAFT) polymerization techniques were used to copolymerize 4-diethylaminostilbene with maleic anhydride. These new semi-rigid copolymers were incorporated into double hydrophilic block copolymers (DHBCS) containing semi-rigid and flexible segments. The subsequent solutions properties of these DHBCs were evaluated with respect to pH and salt responsiveness. Notably, the DHBCs exhibited a "like-charge" attraction as ionic strength increased which was attributed to the semi-rigid character of the polyampholyte block copolymer. / Ph. D.

Surface and bulk properties have been studied in terms of composition and morphology of siloxane containing block copolymers and their blends with homopolymers. X-ray Photoelectron Spectroscopy (XPS) has been used to obtain the compositional information from the top 60 angstroms or so at the surface. Transmission Electron Microscopy (TEM) was utilized to probe the bulk morphology. An attempt is made to compare the bulk and the surface and find possible mechanisms governing them. It is found that solvent-cast neat block copolymers have a uniform layer at the surface that is rich in siloxane whereas their bulk has a microphase-separated domain structure. In case of blends, siloxane enrichment is quite pronounced even at bulk concentrations as low as 0.05% w/w siloxane. Amount of surface siloxane as a function of bulk content is studied with the help of XPS. At the same time, the bulk morphology of these blends is studied by TEM. The changes occurring in the surface and the bulk are found to have similar patterns. It is shown that the observed surface behavior may be related to the bulk morphology. Molecular weight of the blocks in the copolymers is found to be a very important parameter governing both the surface and the bulk properties in the neat copolymers as well as their blends. / Master of Science

Yes / Co-crystallization of polymers with different configurations/tacticities provides access to materials with enhanced performance. The stereocomplexation of isotactic poly(L-lactide) and poly(D-lactide) has led to improved properties compared with each homochiral material. Herein, we report the preparation of stereocomplex micelles from a mixture of poly(L-lactide)-b-poly(acrylic acid) and poly(D-lactide)-b-poly(acrylic acid) diblock copolymers in water via crystallization-driven self-assembly. During the formation of these stereocomplex micelles, an unexpected morphological transition results in the formation of dense crystalline spherical micelles rather than cylinders. Furthermore, mixture of cylinders with opposite homochirality in either THF/H2O mixtures or in pure water at 65 °C leads to disassembly into stereocomplexed spherical micelles. Similarly, a transition is also observed in a related PEO-b-PLLA/PEO-b-PDLA system, demonstrating wider applicability. This new mechanism for morphological reorganization, through competitive crystallization and stereocomplexation and without the requirement for an external stimulus, allows for new opportunities in controlled release and delivery applications. / University of Warwick, Swiss National Science Foundation and the EPSRC. The Royal Society - an Industry Fellowship to A.P.D. The Engineering and Physical Sciences Research Council (EP/G004897/1) - funding to support postdoctoral fellowships for A.P.B. as well as funding for J.S. and M.A.D. through the Warwick Centre for Analytical Science (EP/F034210/1). The Science City Research Alliance and the HEFCE Strategic Development Fund - funding support. Some items of equipment that were used in this research were funded by Birmingham Science City, with support from Advantage West Midlands and part-funded by the European Regional Development Fund.

Yes / We report the crystallization-driven self-assembly of diblock copolymers bearing a poly(L-lactide) block into cylindrical micelles. Three different hydrophilic corona-forming blocks have been employed: poly(4-acryloyl morpholine) (P4AM), poly(ethylene oxide) (PEO) and poly(N,N-dimethylacrylamide) (PDMA). Optimization of the experimental conditions to improve the dispersities of the resultant cylinders through variation of the solvent ratio, the polymer concentration, and the addition speed of the selective solvent is reported. The last parameter has been shown to play a crucial role in the homogeneity of the initial solution, which leads to a pure cylindrical phase with a narrow distribution of length. The hydrophilic characters of the polymers have been shown to direct the length of the resultant cylinders, with the most hydrophilic corona block leading to the shortest cylinders. / EPSRC and the University of Warwick, the Swiss National Science Foundation - Early Postdoc Mobility fellowship (Grant no PBNEP2-142949 to A.P.B.). The Warwick Research Development Fund. Some items of equipment funded by Birmingham Science City: Innovative Uses for Advanced Materials in the Modern World (West Midlands Centre for Advanced Materials Project 2), with support from Advantage West Midlands (AWM) and part funded by the European Regional Development Fund (ERDF).

Yes / Polymer self-assembly in solution is a simple strategy for the preparation of elegant yet complex nanomaterials. However, exhaustive synthesis of the copolymer synthons is often required to access specific assemblies. In this work we show that the blending of just two diblock copolymers with identical block lengths but varying hydrophobic monomer incorporations can be used to access a range of assemblies of intermediate hydrophobic composition. Indeed, the nanostructures produced from blending are identical to those formed with the directly synthesized copolymer of the same composition. This new approach presents researchers with a more efficient and accessible methodology to access precision self-assembled nanostructures, and we highlight its potential by applying it to a demonstrator catalytically active system. / European Science Foundation (ESF), Engineering and Physical Sciences Research Council (EPSRC), United States. Air Force. Office of Scientific Research (AFOSR)

Block copolymers are widely used in both the academic and industrial communities due to their unique properties. With the development of living polymerization techniques, the synthesis of block copolymers with controlled molecular weights and unique architectures has reached an all time high. Here a novel approach to the synthesis of block copolymers, namely polystyrene-b-polyisoprene, using azide-alkyne click chemistry techniques is investigated. Both azido and alkyne-terminated polystyrene were synthesized using ATRP. Azido-terminated polystyrene was synthesized via a substitution reaction between NaN3 and bromo-terminated polystyrene. Alkyne-functionalized polystyrene was synthesized using propargyl 2-bromoisobutyrate as a functional initiator. ¹H NMR and SEC were used to analyze the degree of polymer functionalization. Anionic polymerization techniques were used to synthesize polyisoprene. Polyisoprenyl lithium was reacted with propylene oxide to obtain hydroxyl-terminated polyisoprene. Functionalization of ≥ 90% was demonstrated via flash column chromatography. The aforementioned hydroxyl-terminated polyisoprene was reacted with both 11-chloroundecanoyl bromide and 11-chloroundecanoyl chloride to synthesize halogen-terminated polyisoprene. As with polystyrene, a substitution reaction with NaN3 afforded azido-terminated polyisoprene. Alkyne-functionalized polystyrene was coupled with azido-terminated polyisoprene via click chemistry to create said block copolymers. The reactions were investigated using ¹H and ¹³C NMR, SEC, IR and in some cases TEM. The clicked block copolymers should provide precedent for the synthesis of supramolecular block copolymers. / Master of Science

This research focuses on the utilization of two living polymerization methods, anionic and group transfer, for the synthesis of well defined end functional materials and graft copolymers. Group transfer polymerization was utilized to synthesize acrylic terminal poly(methyl methacrylate) (PMMA) macromonomers of controlled molecular weight and narrow molecular weight distribution. A systematic series of PMMA macromonomers were copolymerized with 2-ethylhexyl acrylate to afford poly(2-ethylhexyl-g-methyl methacrylate) copolymers. These copolymers were synthesized in high yields with a high degree of incorporation of the PMMA macromonomer. These graft copolymers showed little or no phase mixing between the two components as evidenced by differential scanning calorimetry. It was determined by optimization studies that the reaction was complete within 50 hours at 65° C. Increases in initiator concentration surprisingly did not significantly effect homopolymerizations of 2-ethylhexyl acrylate with respect to molecular weight while the efficiency of incorporation of the macromonomer into the graft copolymers increased. End functional hydrogenated poly(butadiene) (HPBd) materials and HPBd-containing graft copolymers were synthesized using anionic polymerization methods. These materials were tested for their ability to act as adhesion promoters between poly(propylene)/EPDM and cycloaliphatic polyurethane coatings. Hydroxyl or carboxyl end functional materials were synthesized where molecular weight and chain microstructure were syStematically varied. Effective adhesion was achieved when the molecular weight of the polymer was approximately 20 kg/mol, the polymer was hydrogenated, contained 90 mole percent or greater 1,2- content in the poly(butadiene) precursor, and contained a functional end group, which may be either hydroxyl or carboxyl. To increase the concentration of functional groups over the above materials graft copolymers were utilized. Acrylic terminal HPBd macromonomers were synthesized and copolymerized with butyl acrylate in combination with either N,N-dimethylacrylamide (DMAA), 2-hydroxyethyl methacrylate (HEMA), methacrylic acid (MA), or t-butyl methacrylate (TBMA). Systematic compositions of these graft copolymers were synthesized and tested for adhesion. The acidic containing graft copolymers provided the most positive adhesion results. In one case the hydroxyl containing material also gave positive adhesion results. The DMAA containing materials failed in all cases. The TBMA route allowed for greater control over the composition of the acidic graft copolymers. / Ph. D.

Multiphase star-like copolymers containing lignin have been synthesized and characterized. All copolymers contained hydroxypropyl lignin (HPL) as the central core. Polycaprolactone (PCL), cellulose propionate (CP) or polystyrene (PS), served as radiating blocks attached to the lignin core in star-like manner. These materials were studied in relation to their structure, morphology, effect on crystallization behavior and application in polymer blends. Three series of semi-crystalline (PCL)_n — HPL have been synthesized with HPL segments of 2,100, 3,500 and 6,400 molecular weight, respectively, and polycaprolactone blocks of varying size. Copolymers were produced by either copolymerizing ɛ-caprolactone or grafting preformed PCL segments onto HPL. The thermal and optical properties of these copolymers were investigated by DSC, DMTA and optical microscopy. The copolymers exhibited variable thermal behavior in relation to composition. The crystallization of PCL blocks was mainly governed by the nature of the HPL phase. PCL block length was another variable that affected crystallinity. The longer the segment, the higher the degree of crystallinity. The compatibility, morphology and mechanical properties of (PCL)_n - HPL copolymers blended with poly(vinyl chloride) were also investigated. Methods used in this study included DSC, DMTA, SEM, TEM and stress-strain testing. The blends were shown to be compatible in all proportions. Mono-hydroxyl terminated cellulose propionate oligomers were synthesized by degradation with hydrogen bromide of a fully substituted, high molecular weight cellulose propionate molecule. Evidence of strict monofunctionality was demonstrated by H-NMR spectroscopy. Thermal analysis results indicated that the oligomers were semi-crystalline and their melting points were functions of molecular weight. (CP)_n — HPL copolymers were synthesized by grafting oligomeric CP segments onto HPL via a coupling agent. The thermal and morphological properties of the copolymers were characterized by DMTA, DSC and TEM. Analysis by thermal methods and by electron microscopy showed strong evidence for microphase separation between HPL and CP segments. Cellulose propionate chains crystallize even at a low degree of polymerization, such as DP 5. The copolymer morphologies exhibit a broad variety of features. They vary from dispersed fibrils to spheres like and alternate lamella type patterns according to composition and molecular weights. The interfacial activity of the copolymers in blends of CP and HPL prepared in the melt state was also investigated. The tensile properties of the ternary blends were altered slightly by the presence of the copolymer. Melt blended cellulose propionate and HPL with low degree of propoxylation forms a miscible system with up to 40% HPL component. The incorporation of 5% of the (CP)_n — HPL copolymer reduces the tensile strength by about 10%. Thermal behavior of melt blended cellulose propionate and HPL with high degree of propoxylation indicates the formation of an incompatible system at any composition. Before the addition of the copolymer the blend exhibits higher toughness, elongation up to 160%, and a Young's modulus of 23 ksi. The copolymer-modified blend shows a decrease in toughness and an increase in tensile strength by about 10%. The synthesis and characterization of (PS)_n — HPL copolymers was accomplished in an analogous manner. When added to blends of PS and HPL, (PS)_n -- HPL produced improved mechanical properties of the blends. Scanning electron microscopy of fracture surfaces demonstrated that the addition of copolymer to the PS/HPL blends improved the adhesion of the two phases. The addition of (PS)_n — HPL copolymer to the 90 PS/10 HPL blend system strongly reduced, by about 10 fold, the particle size of the unmodified blend. No significant difference was observed in the morphology of the 80 PS/20 HPL system. The phases exhibited poor adhesion before and after the addition of copolymer. / Ph. D.

Passive damping has been defined as a key element in vibration control. It is believed that the approach to passive damping could be addressed through the use of carefully designed viscoelastic polymeric materials. This dissertation describes the synthesis and characterization of multiphase, transparent block copolymers that are potential candidates for passive damping applications in large space structures. Relatively high molecular weight polysiloxane-polyarylester block copolymers were prepared by two different synthetic routes. A solution technique was used to synthesize well-defined, perfectly alternating block copolymers by reacting a difunctional silylamine—terminated siloxane oligomer with a difunctional hydroxyl-terminated polyarylester oligomer. A second approach involved the preparation of a segmented (or random) block copolymer by an interfacial, phase—transfer technique in which various polyarylester block lengths are formed <u>during</u> the copolymerization by reacting bisphenol-A, terephthaloyl chloride, and isophthaloyl chloride with a difunctional aminopropyl-terminated siloxane oligomer. To vary the miscibility of the siloxane and ester phases, and in turn the physical properties of the block copolymers, the block molecular weights and the siloxane block compositions (dimethyl, dimethyl-diphenyl, or dimethyl-trifluoropropylmethyl) were controlled. Structure analysis by NMR (proton and silicon) and FTIR verified that the desired starting oligomers and block copolymers were successfully prepared. Intrinsic viscosity measurements, size exclusion chromatography, and the fact that tough transparent films could be solution cast and compression molded indicated that relatively high molecular weight materials were prepared. Due to the high degree of incompatibility of the "soft" siloxane segments and the "hard" ester segments in the block polymers, a two-phase microstructure developed at relatively low block molecular weights. In addition to microphase separation, partial phase mixing was apparent from thermal, mechanical, and microscopic characterization techniques. Compared to a polyarylester homopolymer, the siloxane modified polyarylester block polymers displayed improved resistance to atomic oxygen degradation as seen from x-ray photoelectron spectroscopy and scanning electron microscopy. All physical properties were found to be dependent upon siloxane block composition and copolymer block molecular weights. In conclusion, new siloxane-ester block copolymers were prepared and characterized. They are believed to be potentially useful materials for passive damping applications in the space environment. / Ph. D. / incomplete_metadata