Porphyrins are a class of natural and synthetic aromatic macrocycles that have received extensive investigation because of their unique chemical and optoelectronic properties. They are excellent ligands, photosensitizers and catalysts and serve critical roles in numerous biochemical reactions. Their properties and diverse applications have fascinated chemists from multiple fields, and porphyrins have been investigated in applications such as dye-sensitized solar cells, cancer treatments, and conjugated polymers among others. While porphyrins have made in-roads in multiple fields they have received at best minimal attention in the field of polysiloxane chemistry. Polysiloxanes are a class of inorganic polymers widely used in industrial applications that possess properties including low glass transition temperatures, high thermal and oxidative stabilities, high optical transparency, and low refractive indices that are largely unmatched by organic polymers. These properties, if properly utilized, could compliment those possessed by porphyrins and lead to the development of new applications in the fields of porphyrin and polysiloxane chemistry. Unfortunately, porphyrins and polysiloxanes are not readily compatible with one another and synthetic techniques must be developed to allow for the reliable incorporation of porphyrins into polysiloxane matrices. The objectives of this thesis are to develop strategies that allow for the ready incorporation of porphyrins into polysiloxane materials to improve existing and develop new applications for porphyrin-polysiloxane materials. These investigations led to the development of two techniques for the incorporation of porphyrins into polysiloxanes, the Piers-Rubinsztajn reaction, and ionic crosslinking. Several siloxane and polysiloxane porphyrins were prepared utilizing the Piers-Rubinsztajn reaction. These porphyrins were easily incorporated into silicone elastomers that could be utilized as dielectric, or reactive oxygen species-generating elastomers. Alternatively, ionic crosslinks could be utilized to incorporate the natural porphyrin hemin into silicone elastomers. Elastomers manufactured via this method retained the catalytic capabilities of hemin, opening the door to a new class of synthetic peroxidases. Regardless of the method of application controlling the natural tendency of porphyrins to aggregate was essential to achieving the desired properties. / Thesis / Doctor of Philosophy (PhD) / Porphyrins have attracted the attention of scientists for generations who have sought to exploit their unique chemical, physical, optical, and electronic properties. Their unique properties have led to them being utilized in a multitude of applications. Despite the wide array of applications investigated, the utilization of porphyrins in polysiloxane (silicone) chemistry has received comparatively little attention. Polysiloxanes and porphyrins possess potentially mutually beneficial properties that could lead to the development of interesting materials. Unfortunately, their development is not straightforward, as porphyrins and polysiloxanes are not naturally compatible with one another. Therefore, to realize the potential benefit of porphyrin-polysiloxane materials synthetic techniques must be first developed that allow for the reliable incorporation of porphyrins into polysiloxane matrices Two techniques were investigated for the incorporation of porphyrins into polysiloxanes. The Piers-Rubinsztajn reaction and ionic crosslinking. These methods allowed for the development of materials that had interesting applications including dielectric elastomers, reactive oxygen species generating materials and catalytic elastomers.

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Polysiloxane networks have excellent oxidative and good UV environmental stability, flexibility at low temperatures, and thermal stability at higher temperatures. This wide service temperature range makes these materials a candidate class of materials for high performance adhesives and sealants, and in particular for applications on high speed aircraft. Polar polysiloxane networks were prepared with cyanopropyl substituents to lower any propensity for the materials to swell in hydrocarbon fuels and to improve adhesion to metal substrates. 1,3,5,7-tetramethyl,1,3,5,7-tetrahydrocyclotetrasiloxane (D4H) was hydrosilated with allyl cyanide to yield the corresponding 3-cyanopropylmethylcyclotetrasiloxane monomer (D4CN). Controlled molecular weight oligomers with vinyl termination were prepared in equilibrium reactions using a basic catalyst. These oligomers were then crosslinked with various hydride functional crosslinking reagents to yield model networks for mechanical and adhesion studies. The network properties of nonpolar polydimethylsiloxane (PDMS), polar poly[methyl(3,3,3-trifluoropropyl)siloxane] (PMTFPS), and the novel polar poly(3-cyanopropylmethyl-siloxane) (PCPMS) were investigated as a function of sidechain chemical structures. Effects of increasing crosslink density were investigated for the PDMS networks by adding a difunctional siloxane dimer with vinyl groups. Moduli and tensile strengths increased while percent elongation decreased as the crosslink density was increased. All networks were thermally stable above 300 °C in both air and N2 (when heated at a rate of 10 °C/min.) and exhibited Tgs lower than -55 °C. The polar networks swelled to a much lesser extent (at least one order of magnitude) than the nonpolar networks in hydrocarbons and Jet fuel. Cohesive failure was observed for the polar networks via metal to metal (Al foil substrate to Al and Ti adherends) 180° peel test. The PCPMS elastomers had average load values twice those of the PDMS networks independent of crosslink density. / Master of Science

Nitrile containing siloxane block copolymers were developed as stabilizers for siloxane magnetic fluids. The siloxane magnetic fluids have been recently proposed as internal tamponades for retinal detachment surgery. PDMS-b-PCPMS-b-PDMSs (PDMS = polydimethylsiloxane, PCPMS = poly(3-cyanopropylmethylsiloxane) were successfully prepared through kinetically controlled polymerization of hexamethylcyclotrisiloxane initiated by lithium silanolate endcapped PCPMS macroinitiators. The macroinitiators were prepared by equilibrating mixtures of 3- cyanopropylmethylcyclosiloxanes (DxCN) and dilithium diphenylsilanediolate (DLDPS). DxCNs were synthesized by hydrolysis of 3-cyanopropylmethyldichlorosilane, followed by cyclization and equilibration of the resultant hydrolysates. DLDPS was prepared by deprotonation of diphenylsilanediol with diphenylmethyllithium. It was found that mixtures of DxCN and DLDPS could be equilibrated at 100°C within 5-10 hours. By controlling the DxCN-to-DLDPS ratio, macroinitiators of different molecular weights could be obtained. The major cyclics in the macroinitiator equilibrate are tetramer (8.6 ± 0.7 wt%), pentamer (6.3 ± 0.8 wt%) and hexamer (2.1 ± 0.5 wt%). 2.5k-2.5k-2.5k, 4k-4k-4k, and 8k-8k-8k triblock copolymers were prepared and characterized. These triblock copolymers are transparent, microphase separated and highly viscous liquids. It was found that these triblock copolymers can stabilize nanometer gamma-Fe₂O₃ and cobalt particles in octamethylcyclotetrasiloxane or hexane. Hence PDMS-b-PCPMS -b-PDMSs represent a class of promising steric stabilizers for silicone magnetic fluids. / Master of Science

Les travaux de recherche présentés dans cette thèse concernent la mise au point et l’étude de résines polysiloxanes et de matériaux sol-gel hybrides permettant de développer de nouveaux revêtements de protection pour des applications spatiales. Il s’agit notamment d’assurer le contrôle thermique des véhicules spatiaux et la protection des polymères vis-à-vis de l’oxygène atomique pour les applications en orbite basse. Outre la stabilité en environnement spatial et les contraintes de mise en œuvre, les revêtements doivent présenter des caractéristiques innovantes (température de polymérisation modérée) et être élaborés à partir de matières premières facilement approvisionnables pour éviter tout risque d’obsolescence. / This work presents the formulation and the study of polysiloxane resins and hybrid sol-gel materials to develop new protective coatings resistant to space environment. Spacecraft thermal control and polymer protection towards atomic oxygen are required in Low Earth Orbit applications. Besides the stability in the space environment and the process requirements, the coatings have to exhibit innovative properties (such as a low curing temperature) and be composed of raw materials with easy supply in order to avoid any risk of obsolescence.

A novel sensor using a polymer coated long-period grating (LPG) has been proposed for monitoring levels of organic contaminants in air or water systems. The sensor operates by detecting refractive index changes in the polymer coating as analytes partition in. Polymer coatings used must be able to reversibly and reproducibly absorb contaminants of interest from the sample and have a refractive index just below that of the fiber cladding. The synthesis and characterization of several chemically selective polysiloxanes is described. Pre-polymer materials are made through the catalyzed condensation of silane monomers. Different functional groups are incorporated either through polymerizing functionalized monomers, or by post-functionalizing the polymer through a platinum-catalyzed hydrosilylation reaction. The pre-polymer materials are crosslinked into elastomeric films using titanium(IV) tetraisopropoxide. The polymer refractive index is controlled through altering the ratios of functional groups within the polymer or changing the loading levels of titanium. Four polymers were made, having different functional groups and optimized refractive indices for use on the proposed sensor. The partition coefficients for the polymers with a variety of solvents are calculated and compared. Each polymer was found to have a slightly different chemical selectivity pattern, demonstrating that a set of polymers could be used to generate a sensor array. Partition coefficient data was calculated from the gas phase by considering the change in polymer refractive index as the solvents partitioned into the polymer. The Lorentz-Lorenz equation was used to model the relationship between the change in refractive index and the solvent concentration within the polymer. Finally, polymers were applied to LPGs and used to successfully detect various solvents from the gas phase. This was accomplished by monitoring the entire LPG spectrum, and also by considering loss at a single wavelength using fiber-loop ring-down spectroscopy. / Thesis (Ph.D, Chemistry) -- Queen's University, 2008-09-26 15:28:35.603

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Polymer synthesis and functionalization enabled the tailoring of polymer functionality for additive manufacturing (AM), elastomer, and biological applications. Inspiration from academic and patent literature prompted an emphasis on polymer functionality and its implications on diverse applications. Critical analysis of existing elastomers for AM aided the synthesis and characterization of novel photopolymer systems for lithography-based 3D printing. Emphasis on structure-processing-property relationships facilitated the attainment of success in proposed applications and prompted further fundamental understanding for systems that leveraged poly(dimethyl siloxane)s (PDMS), aliphatic polyesters, polyamides, and polyethers for emerging applications. The thiol-ene reaction possesses many desirable traits for vat photopolymerization (VP) AM, namely that it proceeds rapidly to high yield, does not undergo significant side reactions, remains tolerant of the presence of water or oxygen, and remains regiospecific. Leveraging these traits, a novel PDMS-based photopolymer system was synthesized and designed that underwent simultaneous chain extension and crosslinking, affording relatively low viscosity prior to photocuring but the modulus and tensile strain at break properties of higher molecular weight precursors upon photocuring. A monomeric competition study confirmed chemical preference for the chain-extension reaction in the absence of diffusion. Photocalorimetry, photorheology, and soxhlet extraction measured photocuring kinetics and demonstrated high gel fractions upon photocuring. A further improvement on the low-temperature elastomeric behavior occurred via introduction of a small amount of diphenylsiloxane or diethylsiloxane repeating units, which successfully suppressed crystallization and extended the rubbery plateau close to the glass transition temperature (Tg) for these elastomers. Finally, a melt polymerization of PDMS diamines in the presence of a disiloxane diamine chain extender and urea afforded isocyanate-free polyureas in the absence of solvent and catalyst. Dynamic mechanical analysis (DMA) measured multiple, distinct α-relaxations that suggested microphase separation. This work leverages the unique properties of PDMS and provides multiple chemistries that achieve elastomeric properties for a variety of applications. Similar work of new polymers for VP AM was performed that leveraged the low Tg poly(propylene glycol) (PPG) and poly(tri(ethylene glycol) adipate) (PTEGA) for use in tissue scaffolding, footwear, and improved glove grip performance applications. The double endcapping of a PPG diamine with a diisocyanate and then hydroxyethyl acrylate provided a urethane/urea-containing, photocurable oligomer. Supercritical fluid chromatography with evaporative light scattering detection elucidated oligomer molecular weight distributions with repeat unit resolution, while the combination of these PPG-containing oligomers with various reactive diluents prior to photocuring yielded highly tunable and efficiently crosslinked networks with wide-ranging thermomechanical properties. Functionalization of the PTEGA diol with isocyanatoethyl methacrylate yielded a photocurable polyester for tissue scaffolding applications without the production of acidic byproducts that might induce polymer backbone scission. Initial VP AM, cell viability experiments, and modulus measurements indicate promise for use of these PTEGA oligomers for the 3D production of vascularized tissue scaffolds. Similar review of powder bed fusion (PBF) patent literature revealed a polyamide 12 (PA12) composition that remained melt stable during PBF processing, unlike alternative commercial products. Further investigation revealed a fundamental difference in polymer backbone and endgroup chemical structure between these products, yielding profound differences for powder recyclability after printing. An anionic dispersion polymerization of laurolactam in the presence of a steric stabilizer and initiator yielded PA12 microparticles with high sphericity directly from the polymerization without significant post-processing requirements. Steric stabilizer concentration and stirring rate remained the most important variables for the control of PA12 powder particle size and melt viscosity. Finally, preliminary fusion of single-layered PA12 structures demonstrated promise and provided insight into powder particle size and melt viscosity requirements. / PHD / Additive manufacturing (AM) enables the creation of unique geometries not accessible with alternative manufacturing techniques such as injection molding, while also reducing the waste associated with subtractive manufacturing (e.g. machining). However, AM currently suffers from a lack of commercially-available polymers that provide elastomeric properties after processing. Poly(dimethyl siloxane)s (PDMS) possess distinctive properties due to their organosilicon polymer backbone that include chemical inertness, non-flammability, high gas permeability, and low surface energy. For these reasons, siloxanes enjoy wide-ranging applications from personal care products, contact lenses, elastomeric sealants, and medical devices. This dissertation focuses on the synthesis and functionalization of novel PDMS-, polyether-, polyester-, and polyamide-containing photopolymers or powders for improved performance in diverse applications that employ processing via vat photopolymerization (VP) or powder bed fusion (PBF) AM. Examples from this work include a novel photopolymer composition that undergoes simultaneous chain extension and crosslinking, affording low molecular weight and low viscosity precursors prior to VP-AM but the properties of higher molecular weight precursors, once photocured. Related work involved the characterization and VP-AM of siloxane terpolymers that suppress crystallization normally observed in PDMS, resulting in 3D printed objects that retain their elastomeric properties close to the glass transition temperature (Tg). Separate work leveraged the unique PDMS backbone for the melt polymerization of PDMS diamines in the presence of a chain extender and urea, yielding isocyanate-free PDMS polyureas in the absence of solvent or catalyst. This reaction creates ammonia as the only by-product and avoids the use of isocyanates, as well as their highly toxic precursors, phosgene. Finally, another research direction facilitates the understanding of observed differences in melt stability between commercially-available grades of polyamide 12 (PA12) powders for powder bed fusion. An anionic dispersion polymerization based in the patent literature facilitated further understanding of the polymerization process and produced melt-stable PA12 microparticles directly from the polymerization process, without requiring additional post-processing grinding or precipitation steps for powder production.