Thesis (Ph.D.) - University of St Andrews, January 2009. / Thesis and abstract restricted until 7th January 2014.

In the first Chapter, Polyhomologation, a powerful technique to synthesize well-defined, perfectly linear, polyethylenes with controllable molecular weight, topology and low polydispersity, is presented in the first Chapter. In this Chapter is also discussed the combination of polyhomologation with other polymerization techniques such as Ring Opening Polymerization, ROP, Atom Transfer Radical Polymerization, ATRP, as well as with chlorosilane linking chemistry towards well-defined polyethylene-based macromolecular architectures. In the second Chapter, α,ω-dihydroxy-polyethylene was synthesized by the polyhomologation of dimethylsulfoxonium methylide with 9-thexyl-9-BBN (9-BNN: 9-borabicyclo[3.3.1]nonane), a novel difunctional initiator produced from 9-BBN and 2,3-dimethylbut-2-ene with two active and one blocked sites, followed by hydrolysis/oxidation. The terminal hydroxy groups were used either directly as initiators, in the presence of 1-tertbutyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene) (t-BuP2), for the ring opening polymerization of ε-caprolactone, ε-CL, in order to afford polycaprolactone-b-polyethylene-b-polycaprolactone (PCL-b-PE-b-PCL) or after transformation to ATRP initiating sites in order to polymerize styrene and produce polystyrene-b-polyethylene-b-polystyrene (PSt-b-PE-b-PSt) triblock copolymers. Molecular characterization by 11B, 13C and 1H NMR as well as FTIR, and high-temperature GPC (HT-GPC) confirmed the well-defined nature of the synthesized new difunctional initiator and triblock copolymers. Differential scanning calorimetry was used to determine the melting points and degree of crystallinity of PE and PCL. In the third Chapter, a novel triallylborane initiator was synthesized and used to afford α-allyl-ω-hydroxy-polyethylene by polyhomologation of dimethylsulfoxonium methylide. The α-allyl-ω-hydroxy-polyethylene was then used as a macroinitiator (OH group) for the ROP of ε-CL and LLA to afford well-defined triblock terpolymer of polylactide-b-polyethylene-b-polycaprolactone (PLLA-b-PE-b-PCL). The characterization of all intermediate and final products by 1H NMR, FTIR, and HT-GPC, verified the well-defined nature of the triblock terpolymer. In the fourth Chapter, polyethylene (PE)-based 3- and 4-miktoarm star [PE(PCL)2, PE(PCL)3], as well as H-type [(PCL)2PE(PCL)2] block copolymers (PCL: polycaprolactone), were synthesized by combining polyhomologation, chlorosilane chemistry, and Ring Opening Polymerization (ROP). For the synthesis of miktoarm stars, a hydroxyl-terminated PE-OH, prepared by polyhomologation of dimethylsulfoxonium methylide with a monofunctional boron initiator, reacted with either chloromethyl(methyl)dimethoxysilane or chloromethyltrimethoxysilane. After the hydrolysis of the methoxysilane groups, the produced difunctional or trifunctional macroinitiators were used for the ROP of ε-caprolactone, in the presence of 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene)(t-BuP2). The H-type block copolymers were synthesized using the same strategy but with a difunctional polyhomologation initiator. All intermediates and final products were characterized by HT-GPC, 1H NMR, and FTIR analysis. The thermal properties of the PE precursors and final products were studied by DSC and TGA. In the fifth Chapter, the self-assembly properties of the amphiphilic linear block copolymer PE-b-PCL and 3-miktoarm star copolymers (PE-b-PCL2) were studied in THF, a selective solvent for PCL, by Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM) and Atomic Force Microscope (AFM). All the above findings presented in this dissertation emphasize the utility of polyhomologation for the synthesis of well-defined polyethylene-based complex macromolecular architectures, which is practically impossible through another kind of polymerization, including the catalytic polymerization of ethylene. In the sixth Chapter, the summary of the thesis and some consideration on the subjects of future work are given.

Polylactides (PLA) are thermoplastic materials known for their biodegradability and biocompatibility, and therefore mostly utilized in biomedical applications. PLA-containing block copolymers further expand their application to include commodity materials and even advanced nanoporous materials. This research part of the thesis focuses on the synthesis and characterization of PLA-containing block copolymers, as well as their corresponding stereocomplexes formed by mixing block copolymers containing PLLA and PDLA segments. This work is divided into three parts. First, by using “living” anionic polymerization of styrene (St) and 2-vinylpyridine (2VP) followed by subsequent ethylene-oxide (EO) termination, well-defined hydroxyl-terminated polystyrene (PS) and poly(2-vinylpyridine) (P2VP) were synthesized. The resulting homopolymers were characterized by 1H nuclear magnetic resonance (NMR), size-exclusion chromatography (SEC), and infrared (IR) spectroscopy. The molecular weights were determined by SEC to be 6,200 and 5,500 g.mol-1 for PS and P2VP, respectively. In the second part, the two homopolymers, PS-OH and P2VP-OH were used as the macroinitiators for the ring-opening polymerization (ROP) of D- and L-lactides (D/L-LA) to obtain PS-b-PDLA and P2VP-b-PLLA, respectively. The targeted molecular weights of PLA blocks were varied to be 5,000, 7,000, and 10,000 g.mol-1 In the final part, quantitative stereocomplex formation was achieved by mixing PS-b-PDLA and P2VP-b-PLLA having equimolar PLAs segments. The physical and chemical properties of the diblockcopolymers and their corresponding stereocomplex, as well as the influence of varying the molecular weights of PLA blocks, were investigated by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), and circular dichroism (CD) spectroscopy.

There is an emerging interest in the development of sustainable materials with high performance. Cellulose is promising in this regard as it is a renewablere source with high specific properties, which can be utilized as strong reinforcements in novel biocomposites. However, to fully exploit the potential ofcellulose, its inherent hydrophilic character has to be modified in order toimprove the compatibility and interfacial adhesion with the more hydrophobicpolymer matrices commonly used in composites.In this study, the grafting of poly(ε-caprolactone) (PCL) and poly(L-lactide)(PLLA) from cellulose surfaces, via ring-opening polymerization (ROP) of ε-caprolactone and L-lactide, was investigated. Both macroscopic and nano-sizedcellulose were explored, such as filter paper, microfibrillated cellulose (MFC),MFC-films, and regenerated cellulose spheres. It was found that thehydrophobicity of the cellulose surfaces increased with longer graft lengths, andthat polymer grafting rendered a smoother surface morphology.To improve the grafting efficiency in the ROP from filter paper, both covalent(bis(methylol)propionic acid, bis-MPA) and physical pretreatment (xyloglucanbisMPA)were explored. The highest grafting efficiency was obtained with ROPfrom the bis-MPA modified filter papers, which significantly increased amountof polymer on the surface, i.e. the thickness of the grafted polymer layer.MFC was grafted with PCL to different molecular weights. The dispersability innon-polar solvent was obviously improved for the PCL grafted MFC, incomparison to neat MFC, and the stability of the MFC suspensions was better maintained with longer grafts. PCL based biocomposites were prepared from neat MFC and PCL grafted MFCwith different graft lengths. The polymer grafting improved the mechanical properties of the composites, and the best reinforcing effect was obtained when PCL grafted MFC with the longest grafts were used as reinforcement.A bilayer laminate consisting of PCL and MFC-films grafted with different PCL graft lengths displayed a gradual increase in the interfacial adhesion with increasing graft length.The effect of grafting on the adhesion was also investigated via colloidal probeatomic force microscopy at different temperatures and time in contact. A significant improvement in the adhesion was observed after polymer grafting. / QC 20100730

Biodegradable aliphatic polycarbonates are important components of non-toxic thermoplastic elastomers, which have a variety of medical applications. Industrially, aliphatic polycarbonates derived from six-membered cyclic carbonates such as trimethylene carbonate (TMC or 1,3-dioxan-2-one) are produced via ring-opening polymerization (ROP) processes in the presence of a tin catalyst. It is worth mentioning that TMC is readily obtained by transesterification of 1,3-propanediol with various reagents including phosgene and its derivatives. Therefore, it has been of great interest to investigate greener routes for the production of this important class of polymers. Toward this goal, the synthesis of aliphatic polycarbonates via the metal catalyzed alternative coupling of oxetanes and carbon dioxide represents an attractive alternative. The use of an abundant, inexpensive, non-toxic, and biorenewable resource, carbon dioxide, makes this method very valuable. Furthermore, in this reaction, the sixmembered cyclic carbonate byproduct, TMC, can also be ring-opened and transformed into the same polycarbonate. For over a decade, the Darensbourg research group has successfully utilized metal salen complexes as catalysts for the epoxide/CO2 copolymerization process. Hence, this dissertation focuses on the examination of these complexes as catalysts for the oxetane/CO2 copolymerization reaction and the further elucidation of its mechanism. Chromium(III) salen derivatives in the presence of an azide ion initiator were determined to be very effective catalysts for the coupling of oxetanes and carbon dioxide providing polycarbonates with minimal amounts of ether linkages. Kinetic and mechanistic investigations performed on this process suggested that copolymer formation proceeded by two routes. These are the direct enchainment of oxetane and CO2, and the intermediacy of trimethylene carbonate, which was observed as a minor product of the coupling reaction. Anion initiators which are good leaving groups, e.g. bromide and iodide, are effective at affording TMC, and hence, more polycarbonate can be formed by the ROP of preformed trimethylene carbonate. Research efforts at tuning the selectivity of the oxetane/CO2 coupling process for TMC and/or polycarbonate produced from the homopolymerization of preformed TMC have been performed using cobalt(II) salen derivatives along with anion initiators. Lastly, investigations of this process involving 3-methoxy-methyl-3-methyloxetane will be presented.

Thesis (Ph.D.)--Ohio University, March, 2008. / Abstract only has been uploaded to OhioLINK. Includes bibliographical references (leaves 115-125)

Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010. / Committee Chair: Weck, Marcus; Committee Member: Breedveld, Victor; Committee Member: Fahrni, Christoph; Committee Member: Kelly, Wendy; Committee Member: Lyon, L. Andrew. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Presented diploma thesis deals with the study of ring-opening polymerization (ROP) of caprolactone catalyzed by novel organic and organometallic compounds. In the theoretical part of the thesis a summary of polymerization strategies and catalytic/initiators systems for ROP of polyesters is overviewed on the basis of reported background research. In experimental part a series of caprolactone polymerization runs with the view of polymerization conditions (solution/monomer ratio, catalyst/initiator ratio, monomer/initiator ratio and monomer concentration) at the temperature range of 25-70 °C was carried out. The experimental study was focused on catalytic precursors based on organic carbenes (tBuNCH=CHN+tBu)CH Cl- (NHC-tBu) in tetrahydrofuran solution and complex of aluminium{O,O’-[4,5-P(O)Ph2tz]-AlMe2} Ph = phenyl, tz = triazole, (OAlMe2) in chlorobenzene solution. Obtained polymers were precisely characterized by means of 1H NMR spectroscopy (Bruker Avance), Differential scanning calorimetry (TA Instruments Q 2000) and Gel permeation chromatography (Agilent Technologies 1100 series) methods. The microbial degradability of synthesized polymer sample having Mn = 12 kg/mol, Mw/Mn = 2.5 and crystallinity degree of 53 % was examined. The polymer in the form of melt-pressed films and powder form was bacterially aged in Bacillus subtilis (BS) strain inoculated mineral and nutrient media for 42 days. Scanning electron microscopy (SEM) and Confocal laser scanning microscopy (CLSM) confirmed the crack development on the surface of films as the consequence of microbial attack in comparison with unchanged control samples. Moreover, the pink coloration of polymer suspension was observed as the consequence of bacterial activity.

Ring opening metathesis polymerization (ROMP) is established as one of the efficient controlled living polymerization methods which have various applications in polymer science and technology fields. The research presented in this dissertation addresses several applications of multifunctional well-defined norbornene-based block copolymers synthesized by ROMP using ruthenium-based Grubbs catalysts. These novel block copolymers were applied to stabilize maghemite nanoparticles, creating the superparamagnetic polymeric nanocomposites. The Jaggregation properties of the porphyrin dyes were improved via self-assembly with a customized norbornene polymer. Novel multimodal copolymer probes were synthesized for two-photon fluorescence integrin-targeted bioimaging. In Chapter 1 a brief overview of ROMP along with ruthenium metal catalysts and selected applications of the polymers related to this research is presented. Superparamagnetic maghemite nanoparticles are important in biotechnology fields, such as enhanced magnetic resonance imaging (MRI), magnetically controlled drug delivery, and biomimetics. However, cluster formation and eventual loss of nano-dimensions is a major obstacle for these materials. Chapter 2 presents a solution to this problem through nanoparticles stabiulized in a polymer matrix. The synthesis and chracterization of novel diblock copolymers, consisting of epoxy pendant anchoring groups to chelate maghemite nanoparticles and steric stabilizing groups, as well as generation of nanocomposites and their characterization, including surface morphologies and iv magnetic properties, is discussed in Chapter 2. In Chapter 3, further improvement of the nanocomposites by ligand modification and the synthesis of pyrazole-templated diblock copolymers and their impact to stabilize the maghemite nanocomposite are presented. Additionally, the organic soluble magnetic nanocomposites with high magnetizations were encapsulated in an amphiphilic copolymer and dispersed in water to assess their water stability by TEM. To gain a preliminary measure of biocopatibility of the micelle-encapsulated polymeric magnetic nanocomposites, cell-viability was determined. In Chapter 4, aggregation behaviors of two porphyrin-based dyes were investigated. A new amphiphilic homopolymer containing secondary amine moieties was synthesized and characterized. In low pH, the polymer became water soluble and initiated the stable Jaggregation of the porphyrin. Spectroscopic data supported the aggregation behavior. Two photon fluorescence microscopy (2PFM) has become a powerful technique in bioimaging for non-invasive imaging and potential diagnosis and treatment of a number of diseases via excitation in the near-infrared (NIR) region. The fluorescence emission upon two-photon absorption (2PA) is quadratically dependent with the intensity of excitation light (compared to the linear dependence in the case of one-photon absoprtion), offering several advantages for biological applications over the conventional one-photon absorption (1PA) due to the high 3D spatial resolution that is confined near the focal point along with less photodamage and interference from the biological tissues at longer wavelength (~700-900 nm). Hence, efficient 2PA absorbing fluorophores conjugated with specific targeting moieties provides an even better bioimaging probe to diagnose desired cellular processes or areas of interest The αVβ3 integrin v adhesive protein plays a significant role in regulating angiogenesis and is over-expressed in uncontrolled neovascularization during tumor growth, invasion, and metastasis. Cyclic-RGD peptides are well-known antagonists of αVβ3 integrin which suppress the angiogenesis process, thus preventing tumor growth. In Chapter 5 the synthesis, photophysical studies and bioimaging is reported for a versatile norbornene-based block copolymer multifunctional scaffold containing biocompatible (PEG), two-photon fluorescent (fluorenyl), and targeting (cyclic RGD peptide) moieties. This water-soluble polymeric multi scaffold probe with negligible cytotoxicity exhibited much stronger fluorescence and high localization in U87MG cells (that overexpress integrin) compared to control MCF7 cells. The norbornene-based polymers and copolymers have quite remarkable versatility for the creation of advanced functional magnetic, photonic, and biophotonic materials.

Thesis advisor: Jia Niu / Thesis advisor: Jim Morken / Polysaccharides make up one of the largest classes of nature’s macromolecules. However, they are severely understudied relative to other biomolecules such as proteins and DNA sequences. This is because discrete polysaccharides are difficult to isolate from nature or synthesize in laboratories in large enough quantities for thorough research. Polymerization is an efficient route to polysaccharides, yet has historically suffered from harsh conditions and lack of control. Herein, we investigate recent developments in the field of living polymerization as strategies towards synthesis of precision polysaccharides from 1,2- anhydrosugars. We specifically focus on cationic ring opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) ROP polymerization of 1,2-O-Bn-3,4,6-anhydromannose and 1,2-O-Bn-3,4,6-anhydroglucose. Our research screens various catalyst/initiating systems. Our findings demonstrate that cationic ROP and RAFT polymerization are unsuccessful in the living ROP of 1,2-anhydrosugars. / Thesis (MS) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.