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

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

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 / Uniform onion micelles formed from up to ten nano-structured polymer layers were produced by the aqueous self-assembly of highly-branched copolymers. Highly-branched poly(alkyl methacrylate)s were chain extended with poly(acrylic acid) in a two-step reversible addition–fragmentation chain transfer-self-condensing vinyl polymerization (RAFT-SCVP) in solution. The resulting polymers were dispersed into water from oxolane (THF) using a self-organized precipitation-like method and the self-assembled particles were studied by phase-analysis light scattering, small-angle neutron scattering, and electron microscopy techniques. The relative hydrophobicity of the blocks was varied by changing the alkyl methacrylate (methyl, butyl, or lauryl) and this was found to affect the morphology of the particles. Only the poly(butyl methacrylate)-containing macromolecule formed an onion micelle structure. The formation of this morphology was observed to depend on: the evaporation of the good solvent (THF) during the self assembly process causing kinetic trapping of structures; the pH of the aqueous phase; and also on the ratio of hydrophobic to hydrophilic segments within the copolymer. The lamellar structure could be removed by annealing the dispersion above the glass transition temperature of the poly(butyl methacrylate). To exemplify how these onion micelles can be used to encapsulate and release an active compound, a dye, rhodamine B (Rh B), was encapsulated and released. The release behaviour was dependent on the morphology of the particles. Particles formed containing the poly(methyl methacrylate) or poly (lauryl methacrylate) core did not form onions and although these materials absorbed Rh B, it was continuously released at room temperature. On the other hand, the lamellar structure formed from branchpoly( butyl methacrylate)-[poly(butyl methacrylate)-block-poly(acrylic acid)] allowed for encapsulation of approximately 45% of the dye, without release, until heating disrupted the lamellar structure. / EPSRC and Domino UK Ltd for a Nanotechnology KTN CASE studentship to support SLC, Experiments at the ISIS Pulsed Neutron and Muon Source were supported by a beam time allocation from the Science and Technology Facilities Council (experiment numbers RB1220108 and RB1320167).

It’s becoming more and more difficult to make smaller, denser, and faster computer chips. There’s an increasing demand to design new materials to be applied in current lithographic process to get higher patterning performance. In this work, the aqueous developable single molecule resists were introduced, synthesized and patterned. A new group of epoxide other than glycidyl ether, cyclohexene oxide was introduced to functionalize a molecular core and 15 nm resolution was obtained. The directed self-assembly (DSA) of block copolymers as an alternative lithographic technique has received growing interest in the last several years for performing higher levels of pitch subdivision. A 3-step simplified process for DSA by using a photodefinable substrate was introduced by using a functionalized polyphenol with an energy switchable group and a crosslinkable group. Two high χ block copolymers PS-b-PAA and PS-b-PHEMA were successfully designed and synthesized via ATRP with controlled Mw and PDI. The size of the same PS-b-PAA polymer was tunable by varying the thermal annealing time. PS-b-PHEMA shows to be a suitable block polymer for the industry-friendly thermal annealing process. A self-complementary hydrogen-bonding urea group as a center group was used to facilitate the self-assembly of polymers. “Click” chemistry is promising for synthesis of PS-Urea-Urea-PMMA.

Thesis (PhD (Chemistry and Polymer Science)--University of Stellenbosch, 2005. / This study involves the synthesis and characterisation of PEG-based amphiphilic block copolymers for the hydrophilization of polysulphone ultrafiltration membranes. PEG based macro RAFT agents were synthesized and characterised. PEG-b-PS block copolymers were synthesized via the RAFT assisted controlled free radical polymerisation utilizing the synthesized PEG macro RAFT agents. The resulting polymerisation products were then analyzed by two-dimensional chromatography at the “critical conditions” for PS. In the second phase of this study PEG-b-PSU block copolymers were synthesized via the polycondensation of bis (4-chlorophenyl) sulphone, Bisphenol A, and PEG. The resulting products were characterised by NMR spectrometry. PEG-b-PS films and modified PSU membranes (modified by the addition of PEG-b-PSU block copolymer to the membrane casting solution) were prepared and analyzed. Surface analyses included static contact angle, AFM force-distance analysis, and FTIR-PAS analysis. Results showed the successful synthesis of both PEG-b-PS and PEG-b-PSU amphiphilic block copolymers. Surface analysis proved the successful hydrophilization of the surface of the modified PSU membranes.

The structure-property relationships for various segmented copolymers were investigated. A number of mechanical and thermal characteristics were determined. The morphology was characterized by SAXS with respect to size and dispersion of domains; degree of phase separation and the domain interfacial thickness. a. Novel segmented copolymers were synthesized using amino terminated polydimethylsiloxane oligomers as the soft component and various hard component. lt was found that the performance of these copolymers was affected by the varying the hard segment linkages, hard segment content, soft segment MW, stiffness of the siloxane backbone, and amount of chain extender. Two-phase nature of these copolymers was verified by dynamic mechanical, thermal, and SAXS studies. The phase separation was found to occur in these copolymers with as little as 6% HS. These materials displayed behavior similar to the segmented polyurethanes and were found to be superior to the unfilled silicone elastomers. The final materials were used as reasonable models for investigating various methods for determining the interfacial layer thickness between the hard and soft phase. Specifically, due to the fact that there is no hard segment length distribution as is the usual case for segmented urethanes, these materials have some degree of model characteristics. Utilizing Porod's law, and appropriate analysis, both positive and negative deviations were found in the systematic series of copolymers with the degree of positive and negative character dependent upon composition. Negative deviations were accounted for in terms of a finite interfacial thickness which turned out to be relatively small as anticipated, while the positive deviations arose due to isolated hard segments that reside within the soft segment matrix, concentration fluctuations. ln calculating the interfacial thickness, several methods were applied and in general, close agreement was obtained. Finally, correlation function analysis in conjunction with determination of the coherent Porod lengths, etc. were determined and discussed accordingly. b. The structure-property behavior of novel 'water extended' segmented polyurethane-urea copolymers was also investigated. These copolymers were synthesized by utilizing the dehydration characteristics of tertiary alcohols at sufficiently high temperature in weak acidic medium. Mechanical, thermal, dynamic mechanical, and x-ray experiments were carried out to characterize the morphology and properties of these segmented copolymers of systematically varying hard segment content, soft segment MW, block length, and hard segment type. lt was observed that these properties depended primarily on the degree of order in the hard domains and the order could be improved by increasing either the HS content at constant soft segment MW or soft segment molecular weight at the same HS content. The results obtained for these materials were compared with those from conventional polyurethanes to investigate the effect of intermolecular hydrogen bonding on molecular arrangement. c. The final series of segmented copolymers studied were based on polysulfone and polydimethylsiloxane, synthesized by solution polymerization. lt is shown that by varying the length of the segments for each phase and their relative content, it is possible to alter the mechanical and thermal characteristics. The mechanical response was also influenced according to which phase is predominantly continuous. In addition to dynamic mechanical and SAXS measurements, the evidence of the two-phase structure was obtained by TEM. / Ph. D. / incomplete_metadata

Dissertation (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Polymers prepared via radical techniques are very common in our every day environment. The technique is however limited by a lack of control over the polymerization and an inability to produce block copolymers. Block copolymers have a significant number of potential applications in advanced materials and as a result are a field in which significant research is being conducted. Reversible Addition-Fragmentation chain transfer (RAFT) is a living free radical process that overcomes the disadvantages inherent in the traditional process. In this study the mediation behaviour of two inherently different RAFT agents was investigated by the “living” free radical polymerization of model monomers via the RAFT process in homogeneous and aqueous dispersed media with the focus on differentiating between the two types of agents. To ensure that the agents were comparable a new RAFT agent had to be prepared which has not previously been documented. The efficiency of the RAFT agents was compared in terms of rate effects, the predictability of the molecular weights of the polymers, the polydispersities of the polymers and their ability to allow block copolymer formation via sequential addition of monomers. Block copolymerizations were conducted by the addition of new monomer to the already existing RAFT end-capped chains. Monomer addition was done via three different approaches; namely shot addition, feed addition and pre-swelling (in the case of emulsions). Chromatographic analysis was conducted on the resulting block copolymers via liquid chromatography at critical conditions (LCCC), and its online coupling with size-exclusion chromatography (SEC) to obtain two-dimensional information on the differences in heterogeneity of their molecular distributions. Other analyses included dynamic light scattering analysis (DLS) and transmission electron microscopy (TEM). The detailed analysis enabled the understanding of the different products that are produced via the two different classes of RAFT agent. Potential causes for the differences are discussed and possible areas for future research are highlighted. The work presented here is the most detailed investigation of this class of polymerization to date and will provide new insight for researchers working in this vibrant and important research field. / AFRIKAANSE OPSOMMING: Polimere gesintetiseer deur die gebruik van radikaal tegnieke is algemeen in ons daaglikse omgewing. Die tegniek is egter beperk deur die gebrek aan beheer oor die polimerisasie en die onvermoë om blokkopolimere te sintetiseer. Blokkopolimere beskik oor ‘n aansienlike hoeveelheid potensiele aanwendinge in gevorderde materiale en is gevolglik ‘n belangrike navorsingsgebied. Omkeerbare addisie fragmentasie ketting oordrag (OAFO) is ‘n lewende vrye radikaal proses wat die inherente nadele van die tradisionele proses oorkom. In die betrokke studie is die mediasie gedrag van twee verskillende OAFO agente bestudeer deur die lewende vrye radikaal polimerisasie van model monomere deur die OAFO proses in homogene en waterig dispersie media met die fokus op differensiering tussen die twee tipes agente. Om te verseker dat die twee agente vergelykbaar is, is ‘n nuwe OAFO agent voorberei wat tot op hede nog nie gedokumenteer is nie. Die effektiwiteit van die OAFO agente is vergelyk in terme van tempo effekte, die voorspelbaarheid van die molekulêre massa van die polimere, die polidispersiteit van die polimere en die moontlikheid om blokkopolimerisasie deur kronologiese byvoeging van monomere te fasiliteer. Blokkopolimerisasie is uitgevoer deur die byvoeging van nuwe monomeer tot die alreeds bestaande OAFO eind-groep kettings. Monomeer byvoegings is uitgevoer deur drie verskillende metodes; naamlik vulskoot addisie, voer addisie en vooraf swelling (in die geval van emulsies). Chromatografiese analise is uitgevoer op die resulterende blokkopolimere deur vloeistof chromatografie by kritieke kondisie (LC-CC) en die aanlyn koppeling met grootte-uitsluiting vloeistof chromatografie, om twee-dimensionele informasie omtrent die verskille in heterogeniteit van hul molekulere verdeling te bepaal. Verdere analise sluit dinamiese verstrooing mikroskopie en transmissie elektron mikroskopie in. Die detaileerde analise onthul die samestelling van die verskillende produkte wat geproduseer is deur die verskillende klasse van OAFO agent. Potensiele oorsake vir die verskille is bespreek en moontlike areas vir toekomstige navorsing is benadruk. Die werk hier voorgestel is die mees gedetaileerde navorsing van hierdie tipe klas van polymerisasie tot op hede en beloof nuwe insig vir navorsers betrokke in hierdie dinamiese en belangrike navorsingsveld.