Polymer-Based membranes play a critical role in several industrially important gas separation processes, e.g., carbon dioxide removal from natural gas. However, an intrinsic trade-off between membrane flux (characterized by its permeability) and selectivity to one gas over the other has limited their effectiveness in practical environments. While some incremental success has been obtained by empirically developing new polymer chemistries, the best hopes for transformative improvements may require novel architectures employing predictive structure/property relationships. In this work, we develop a novel hybrid membrane construct comprised of inorganic nanoparticles grafted with polymer chains to form grafted nanoparticles. We find that the grafting architecture almost exclusively results in enhanced gas transport properties, in contrast with those expected from conventional predictions. These enhancements, found to be a result of elevated diffusion constants, are broadly tunable with the grafted chain length and leads to order of magnitude increases in gas permeability. We conjecture that the grafted polymer chains serve to impart added free volume to the composite material, which manifests itself as enhanced gas diffusion relative to the pure polymer. Indeed, multiple experimental and simulation probes verify this picture, and indicate that the free volume increases are a result of the grafted chains adopting anisotropic conformations to fill space. Building off of this finding, we systematically study the effects of the nanoparticle core size and chain grafting density, and find that both the chain length where the maximum permeability occurs, as well as the extent of the enhancement, varies depending on the relative sizes of the chains and the nanoparticle. A thorough structural analysis of the grafted nanoparticles in dilute solution as well as bulk samples indicate that the relation between the measured polymer brush height and the chain length undergoes a transition at intermediate chain lengths, similar to the observed gas permeability enhancements. Using a simple scaling approach, we show that this transition is related to the crossover from a concentrated polymer brush with higher order scaling to a semi-dilute brush where the chains are more ideal. We hypothesize that this impenetrable concentrated brush phase is the source of the added free volume, and that this effect is diminished when the grafted chains are longer than the transition point and the penetrable, semi-dilute polymer brush begins to dominate gas diffusion. When cast in the framework of free volume theories, this prediction accurately captures the trends in gas diffusion; the result is a unique structure/property relation that can be used to design optimal membrane materials. We expand on these constructs to probe other grafted nanoparticle-based architectures incorporating free polymer chains and advanced chemistries to further manipulate the gas transport properties of these mixed-matrix materials. The addition of free chains with judiciously chosen molecular weights and loadings gives a nearly independent means to tune membrane selectivity, which when combined with the intrinsic permeability increases in the matrix-free grafted nanoparticles results in superior materials that can exceed the current performance Upper Bound. We relate this result to the spacial distribution of the free chains throughout the grafted polymer corona, and how this affects the distribution of the free volume in the material as it selectively cuts off larger gas molecules. We further leverage this universal grafting platform by grafting polymer chains with novel chemistries to design membranes with record-setting selectivities while also increasing permeability by nearly two orders of magnitude. We conclude that grafted nanoparticle constructs allow for precise and predictive control of gas transport properties through a new structure/property relation, and serve as a novel material design platform with the potential to function as high performance gas separation technologies.

In Chapter 1-3, properties and applications of block copolymers, synthetic methods especially living anionic polymerization as well as the development of the SAAP concept with some of previous successful examples are reviewed. Experimental methods, including the design and establishment of a special high-vacuum system, size exclusion chromatography and laser light scattering, are explained. / In Chapter 4, living anionic polymerization of alpha,o-di bromobutyl end-capped PI-b-PS-b-PI triblock copolymers and the end-capping reaction with 1,4-dibromobutane at the end of polymerization are described, including a in-depth analysis of the reaction mechanism that involves the dimerization of two living oligomer chain during the reaction of living polymeric anions with haloalkanes, i.e., the Wurtz-type coupling reaction. The self assembly and coupling reaction of 1,4-dilithio-1,1,4,4-tetraphenylbutane (DD2-) in n-hexane to form long (PI- b-PS-b-PI)10 multiblock chains are discussed. The coupling efficiencies with and without the self assembly are compared to demonstrate the principle of SAAP. However, the coupling reaction with dianion linker is troublesome because a trace amount of impurities in the solvent can remove its activity. / In Chapter 5, a method of improving the coupling efficiency is described. In this method, PI-b-PS-b-PI triblock copolymers is end-capped with avo-dicarboxylic acid groups via a reaction between living anions and carbon dioxide. Such prepared HOOC-ISI-COOH chains can be coupled with 1,6-hexamethylenediamine (HDA) in the presence of 1,3-dicyclohexylcarbodiimide (DCC) after the self assembly. The size exclusion chromatography (SEC) analysis shows that the SAAP method mainly leads to the formation of triblock copolymer chain dimers and the coupling efficiency is close to 50%. There is no coupling in THF without the self assembly. Further, a much better method of using alpha,o-diacyl chloride end-capped PI-b-PS-b-PI triblock copolymer chains in SAAP to prepare long multiblock copolymer chains is described. Using this recently developed method, we are able to prepared long ∼90-block copolymer chains (PI-b-PS-b-PI)30 which clearly shows the advantage of using SAAP to prepare long multiblock copolymers with a controllable sequence and different block lengths. / In this thesis, we have proposed and developed a novel method: The Self-Assembly Assisted Polypolymerization (SAAP). Namely, using the self-assembly of A-B-A triblock copolymers with two active end groups in a selective solvent for the A-block to concentrate and expose the active end groups on the periphery of the resultant core-shell polymeric micelles, we can effectively couple each two active ends on different chains together to form a long multiblock copolymer chain with its sequence and block length well controlled by the initial triblock copolymer. To accomplish this project, we first built a high-vacuum system for living anionic polymerization and then synthesized and characterized narrowly distributed polyisoprene-b-polystyrene- b-polyisoprene (PI-b-PS-b-PI) triblock copolymer chains with their both ends capped respectively with bromobutyl and carboxylic acid active groups. The self assembly of such prepared triblock copolymers in n-hexane, a selective solvent for PI, was studied by a combination of static and dynamic laser light scattering (LLS). Finally, the self-assembled end-functionalized PI-b-PS-b-PI chains were coupled together by difunctional small molecules (linkers) to form long multiblock copolymers with a controlled structure. / Hong, Liangzhi. / "Aug 2007." / Adviser: Chi Wu. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1036. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

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Doctor of Philosophy (PhD), Engineerig / Free radical emulsion polymerization (FRP) is widely adopted in industry due to its applicability to a wide range of monomers. Despite its many benefits and wide spread use, the fast chain growth and the presence of rapid irreversible termination impose limitations with respect to the degree of control in FRP. Furthermore, producing block copolymers and polymers with complex structures via FRP is not feasible. Closer control of macromolecular chain structure and molar mass, using novel polymerization techniques, is required to synthesize and optimize many new polymer products. Reversible addition fragmentation chain transfer (RAFT)-mediated polymerization is a novel controlled living free radical technique used to impart living characters in free radical polymerization. In combination with emulsion polymerization, the process is industrially promising and attractive for the production of tailored polymeric products. It allows for the production of particles with specially-tailored properties, including size, composition, morphology, and molecular weights. The mechanism of RAFT process and the effect of participating groups were discussed with reviews on the previous work on rate retardation. A mathematical model accounting for the effect of concentrations of propagating, intermediate, dormant and dead chains was developed based on their reaction pathways. The model was combined with a chain-length dependent termination model in order to account for the decreased termination rate. The model was validated against experimental data for solution and bulk polymerizations of styrene. The role of the intermediate radical and the effect of RAFT agent on the chain length dependent termination rate were addressed theoretically. The developed kinetic model was used with validated kinetic parameters to assess the observed retardation in solution polymerization of styrene with high active RAFT agent (cumyl dithiobenzoate). The fragmentation rate coefficient was used as a model parameter, and a value equal to 6×104 s-1 was found to provide a good agreement with the experimental data. The model predictions indicated that the observed retardation could be attributed to the cross termination of the intermediate radical and, to some extent, to the RAFT effect on increasing the average termination rate coefficient. The model predictions showed that to preserve the living nature of RAFT polymerization, a low initiator concentration is recommended. In line with the experimental data, model simulations revealed that the intermediate radical prefers fragmentation in the direction of the reactant. The application of RAFT process has also been extended to emulsion polymerization of styrene. A comprehensive dynamic model for batch and semi-batch emulsion polymerizations with a reversible addition-fragmentation chain transfer process was developed. To account for the integration of the RAFT process, new modifications were added to the kinetics of zero-one emulsion polymerization. The developed model was designed to predict key polymer properties such as: average particle size, conversion, particle size distribution (PSD), and molecular weight distribution (MWD) and its averages. The model was checked for emulsion polymerization processes of styrene with O-ethylxanthyl ethyl propionate as a RAFT based transfer agent. By using the model to investigate the effect of RAFT agent on the polymerization attributes, it was found that the rate of polymerization and the average size of the latex particles decreased with increasing amount of RAFT agent. It was also found that the molecular weight distribution could be controlled, as it is strongly influenced by the presence of the RAFT based transfer agent. The effects of RAFT agent, surfactant (SDS), initiator (KPS) and temperature were further investigated under semi-batch conditions. Monomer conversion, MWD and PSD were found to be strongly affected by monomer feed rate. With semi-batch mode, Mn and <r> increased with increasing monomer flow rate. Initiator concentration had a significant effect on PSD. The results suggest that living polymerization can be approached by operating under semi-batch conditions where a linear growth of polymer molecular weight with conversion was obtained. The lack of online instrumentation was the main reason for developing our calorimetry-based soft-sensor. The rate of polymerization, which is proportional to the heat of reaction, was estimated and integrated to obtain the overall monomer conversion. The calorimetric model developed was found to be capable of estimating polymer molecular weight via simultaneous estimation of monomer and RAFT agent concentrations. The model was validated with batch and semi-batch emulsion polymerization of styrene with and without RAFT agent. The results show good agreement between measured conversion profiles by calorimetry with those measured by the gravimetric technique. Additionally, the number average molecular weight results measured by SEC (GPC) with double detections compare well with those calculated by the calorimetric model. Application of the offline dynamic optimisation to the emulsion polymerization process of styrene was investigated for the PSD, MWD and monomer conversion. The optimal profiles obtained were then validated experimentally and a good agreement was obtained. The gained knowledge has been further applied to produce polymeric particles containing block copolymers. First, methyl acrylate, butyl acrylate and styrene were polymerized separately to produce the first block. Subsequently, the produced homopolymer attached with xanthate was chain-extended with another monomer to produce block copolymer under batch conditions. Due to the formation of new particles during the second stage batch polymerization, homopolymer was formed and the block copolymer produced was not of high purity. The process was further optimized by operating under semi-batch conditions. The choice of block sequence was found to be important in reducing the influence of terminated chains on the distributions of polymer obtained. It has been found that polymerizing styrene first followed by the high active acrylate monomers resulted in purer block copolymer with low polydispersity confirmed by GPC and H-NMR analysis.

This work focuses on binary chemical nano-patterning and on aspects related to the self-organization and stability during and after dewetting of thin block-copolymer films on chemically nano-patterned substrates. Regarding surface functionalization with thiols, the exchange of thiols in both liquid and gas phase was first investigated. The aim was to control thiols-assembly on gold and thus to fabricate unscrambled binary chemical nano-patterns. The systems gold-thiols are considered as alternatives to silicon oxide-silanes systems in the chemical nano-patterning processes because of fabrication simplicity reasons. The strategy developed to avoid thiol exchange was used to fabricate unscrambled binary chemical nano-patterns combining a top-down approach, Electron Beam Lithography (EBL), and a bottom-up approach based on the self-assembly of thiols on gold. Than, using the chemically nano-patterned surfaces previously developed, the organization processes of thin block-copolymer films were studied. Thin symmetric and asymmetric diblock copolymer films were deposited on engineered substrates consisting of alternating less and more wettable stripes. By locally tuning the chemical properties of the substrate, the interaction potential between the polymer and the substrate can be manipulated. It was thus possible to force a liquid film to dewet or to self-organize in a variety of configurations through phase preparation, specific interactions, confinement.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Mary E. Galvin-Donoghue, Dept. of Materials Science & Engineering. Includes bibliographical references.

Recently, a particular interest has been devoted to “smart”/stimuli-responsive amphiphilic polymeric materials. Strictly speaking, such structures do not present an amphiphilic character but can be transformed as such by external stimuli within their close environment, e.g., pH, temperature, light, ionic strength, ... and are then able to produce reversible self-assemblies greatly attractive in the biomedical field as drug delivery systems. The originality of this thesis relies upon the synthesis of “intelligent” hydrophilic triblock copolymers containing acrylamide and acrylate-based monomers presenting both thermo- and pH-responsiveness. The applied synthetic strategy aimed at performing the controlled copolymerization reactions entirely in aqueous conditions and in a “one-pot process” via Atom Transfer Radical Polymerization (ATRP). This synthetic approach represents a real challenge knowing that ATRP of (meth)acrylamide comonomers is difficult to control in aqueous medium. However, by the help of kinetic studies and related theoretical modeling, a fine control over the copolymerization process has been made available allowing the synthesis of polyacrylamide-based triblock copolymers with different charge states. Ultimately, all series of triblock copolymers have been investigated for forming polyelectrolyte complexes potentially useful as drug delivery (nano)systems. The first part of the thesis aims at reporting the control and the understanding of the aqueous ATRP of N-isopropylacrylamide (NIPAAm) initiated by a model low molecular weight initiator. The NIPAAm polymerization has been kinetically studied varying different parameters. Correlated with a theoretical modeling, the reactions involved in the ATRP process have been identified highlighting the importance of molecular diffusion limitations. This step was crucial in view to extrapolate to the synthesis of poly(N-isopropylacrylamide)-based copolymers. The second part focuses on the controlled synthesis of poly(ethylene oxide)-b-poly(N- isopropylacrylamide) diblock copolymers using the macroinitiator method. Different conditions such as solvent mixture, nature of the catalyst and of macroinitiator, i.e., poly(ethylene oxide), have been studied ultimately yielding well-tailored polyacrylamide-based triblock copolymers based on NIPAAm, N,N-dimethylaminoethyl acrylate and 2-acrylamido-2-methyl-1-propane sodium sulfonate comonomers The “smart” character of the resulting triblock copolymers has been investigated affording in specific conditions micellar self-assemblies. Last but not least, polyelectrolyte complexes have been prepared by coulombic interactions between the resulting triblock copolymers, e.g., poly(ethylene oxide)-b-poly(N- isopropylacrylamide)-b-poly(N,N-dimethylaminoethyl acrylate) and poly(ethylene oxide)-b- poly(N-isopropylacrylamide)-b-poly(2-acrylamido-2-methyl-1-propane sodium sulfonate) whose the thermo-responsiveness could be highlighted. The so-formed polyelectrolyte complex nanoparticles constitute promising nanovectors of the third generation able to kinetically tune the drug release in function of local temperature variation.

Thesis (M.S.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 18).

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2004. / Collard, David, Committee Co-Chair ; Schiraldi, David, Committee Member ; Liotta, Charles, Committee Member ; Weck, Marcus, Committee Member ; Srinivasarao, Mohan, Committee Member ; Kumar, Satish, Committee Co-Chair. Vita. Includes bibliographical references.

Block copolymers are an ideal solution for a wide variety of nanolithographic opportunities due to their tendency to self-assemble on nanoscopic length scales. High etch selectivity and thin-film orientation are crucial to the success of this technology. Most conventional block copolymers have poor etch selectivity; however, incorporating silicon into one block produces the desired etch selectivity. A positive side effect of the silicon addition is that the χ value (a block-to-block interaction parameter) of the block copolymer increases. This decreases the critical dimension of potential features. Unfortunately, one negative side effect is the increase in the surface energy difference between the blocks. Incorporating silicon decreases the surface energy of that block. Typically, annealing is used to induce the chain mobility that is required for the block copolymer to reach its minimum thermodynamic energy state. Thermal annealing is the easiest annealing technique; however, if the glass transition temperature (Tg) of one block is above the thermal decomposition temperature of the other block, the latter will degrade before the former can reorient. In addition, annealing silicon-containing block copolymers usually results in a wetting layer and parallel orientation since the lower surface energy block favors the air interface, minimizing the free energy. Solvent annealing replaces the air interface with a solvent, thereby changing the surface energy. The solvent plasticizes the block copolymer, effectively decreasing the Tgs of both blocks. Another benefit is the ability to reversibly alter the orientation by changing the solvent or solvent concentration. The challenge with solvent annealing is that it depends on a number of parameters including: solvent selection, annealing time, and vapor concentration, which generate a very large variable space that must be searched to find optimum screening conditions. / text