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This study examined several features of flexible polyurethane foams from a structure-property perspective. A major part of this dissertation addresses the issue of connectivity of the urea phase and its influence on mechanical and viscoelastic properties of flexible polyurethane foams and their plaque counterparts. Lithium salts (LiCl and LiBr) were used as additives to systematically alter the phase separation behavior, and hence the connectivity of the urea phase at different scale lengths. Macro connectivity, or the association of the large scale urea rich aggregates typically observed in flexible polyurethane foams was assessed using SAXS, TEM, and AFM. These techniques showed that including a lithium salt in the foam formulation suppressed the formation of the urea aggregates and thus led to a loss in the macro level connectivity of the urea phase. WAXS and FTIR were used to demonstrate that addition of LiCl or LiBr systematically disrupted the local ordering of the hard segments within the microdomains, i.e., it led to a reduction of micro level connectivity or the regularity in segmental packing of the urea phase. Based on these observations, the interaction of the lithium salt was thought to predominantly occur with the urea hard segments, and this hypothesis was confirmed using quantum mechanical calculations. Another feature of this research investigated model trisegmented polyurethanes based on monofunctional polyols, or "monols", with water-extended toluene diisocyanate (TDI) based hard segments. The formulations of the monol materials were maintained similar to those of flexible polyurethane foams with the exceptions that the conventional polyol was substituted by an oligomeric monofunctional polyether of ca. 1000 g/mol molecular weight. Plaques formed from these model systems were shown to be solid materials even at their relatively low molecular weights of 3000 g/mol and less. AFM phase images, for the first time, revealed the ability of the hard segments to self-assemble and form lath-like percolated structures, resulting in solid plaques, even though the overall volume of the system was known to be dominated by the two terminal liquid-like polyether segments. In another aspect of this research, foams were investigated in which the ratios of the 2,4 and 2,6 TDI isomers were varied. The three commercially available TDI mixtures, i.e., 65:35 2,4/2,6 TDI, 80:20 2,4/2,6 TDI, and 100:0 2,4/2,6 TDI were used. These foams were shown to display marked differences in their cellular structure (SEM), urea aggregation behavior (TEM), and in the hydrogen bonding characteristics of the hard segments (FTIR). Finally, the nanoscale morphology of a series of 'model' segmented polyurethane elastomers, based on 1,4-butanediol extended piperazine based hard segments and poly(tetramethylene oxide) soft segments, was also investigated using AFM. The monodisperse hard segments of these 'model' polyurethanes contained precisely either one, two, three, or four repeating units. Not only did AFM image the microphase separated morphology of these polyurethanes, but it also revealed that the hard domains preferentially oriented with their long axis along the radial direction of the spherulites which they formed. / Ph. D.

The main focus of this dissertation was on characterizing the viscoelastic behavior of a set of four flexible slabstock water-blown polyurethane foams with varying hard segment content as well as solid plaques made from these foams. Three viscoelastic tests; tensile stress relaxation, compression load relaxation, and compression creep, were utilized to evaluate the behavior of these materials at constant temperature and/or relative humidity, RH. The tensile stress relaxation tests were performed at a 25 percent strain level. The majority of the compression load relaxation tests were conducted at a 65 percent level since this is the strain level used for the common indentation load deflection test for flexible foams and the relaxation behavior was rather independent of strain at this level. Over a three hour testing period, a near linear relationship for the log of tensile stress or compressive load versus log time is observed for most conditions. The slope from this linear relationship in tension or the stress decay rate is similar for all the foams and their respective plaques; thus indicating that the tensile stress relaxation of these materials is governed by the solid portion of the foams and is therefore independent of the cellular textures. In addition, the rates of relaxation for rather linear behavior in tension and compression are also comparable for these foams and this implies that the relaxation in compression is mostly independent of the cellular texture of the foams at a 65 percent strain level. After a short induction period, the compressive creep behavior exhibits rather linear behavior for linear strain vs log time over a three hour period. The slope of this relationship is dependent on the initial strain level and goes through a maximum with initial strain at 40 percent. This maximum is believed to be due to the buckling of the foam’s struts. The results for the creep behavior were evaluated at a 65 percent initial strain since the creep behavior is believed to be mostly independent of the cellular texture of the foam at this level and greater. A greater amount of viscoelastic decay, i.e. tensile stress relaxation, compression load relaxation and com- pression creep is observed for the higher hard segment foams. Temperature has a similar effect on the results obtained from the three viscoelastic tests. Likewise, relative humidity at a constant temperature also has a similar effect on the viscoelastic behavior of the three tests. Up to 100°C, temperature accelerates the viscoelastic decay of these foams over a three hour time period. For all three viscoelastic tests, a significant increase in the viscoelastic decay at temperatures greater than 100°C is observed. The FTIR thermal analysis of the plaques indicated that this significant increase is due to additional hydrogen bond disruption as well as possible degradation in the urea and urethane links. Increasing relative humidity at a given temperature does bring about a steady decrease in the initial load or initial stress as well as a small increase in the rate of viscoelastic decay. Overall, the effects of temperature are greater on the viscoelastic decay than humidity. The morphology and the viscoelastic behavior of another set of flexible slabstock foams were characterized. These additional foams are rather unique in that some of their morphological features, the urea aggregate structure in particularly, are altered by adding a small amount of LiCl to the formulation. As discussed within the body of this dissertation, these observed changes in morphology are believed to have a significant effect on the viscoelastic nature. / Ph. D.

Rotaxane chemistry provides a new direction of research in polymer architectures. Unlike conventional polymers, polyrotaxanes are molecular composites comprised of macrocycles threaded by linear polymer backbones with no covalent bonds between the two components. This novel class of materials displays unusual chemical and physical properties due to their unique architectures. The studies include crown ether and blocking group syntheses, synthetic methodologies leading to rotaxanes and polyrotaxanes and structure-property relationships of polyrotaxanes. Crown ethers (30-crown-10, 36-crown-12, 42-crown-14, 48-crown-16 and 60-crown-20) were systematically synthesized from low molecular weight glycols with 30 - 60% yields. Bis(p-phenylene)-32-crown-4 and bis(p-phenylene)-34-crown-10 (BPP34C10) were also synthesized in 8 - 13% yields; the latter was synthesized with four different synthetic routes. All crown ethers were prepared in large quantities. A series of monofunctionalized triaryl derivatives were also synthesized as rotaxane blocking groups. A series of polyrotaxanes comprised of a polyurethane backbone and crown ethers with ring size ranging from 36 - 60 membered were synthesized via the statistical threading method. The polyrotaxane formation was proven by multiple reprecipitations, ¹H-NMR and GPC analyses. The threading efficiency (rings per repeat unit) increases from 0.16 to 0.87 with an increase in ring size of crown ethers from 36 to 60 membered at 1.5 molar ratio of crown ether to linear glycol. Host-guest complexation of paraquat dication and BPP34C10 has been studied. A series of difunctionalized paraquat dication derivatives was synthesized and used to prepare host-guest complexes (pseudorotaxanes) with BPP34C10. X-Ray crystal structures of the complexes were determined. Furthermore, a class of viologen-containing polyurethane elastomeric polyrotaxanes was synthesized via this host guest complexation. The threading efficiencies from this method were quantitative. Through rotaxane formation, polymer solubilities increase and glass transition temperatures decrease. Evidenced by DSC and WAXS analyses, the crown ether forms crystalline domains without dethreading from the amorphous polyurethane backbone. This process is kinetically "retarded". It is time and temperature dependent and reversible. It can only be observed for polyrotaxanes with large rings and high ring contents, which provide high mobilities of rings along the backbone and also wide T_m - T_g windows. The study of recrystallization kinetics has also shown that 60-crown-20 recrystallizes much slower in a polyrotaxane than in its physical blend with the model polymer. / Ph. D.

Hydroxypropyl lignins (HPLs) from several sources were reacted with propylene oxide to produce chain-extended ) hydroxypropyl lignin (CEHPL) copolymers with molar substitutions (MS) between 1 and 7 propylene oxide units. Isolated copolymers were characterized with respect to their chemical composition, molecular weight and thermal properties. These techniques confirmed the presence of a copolymer with between 20 and 67% lignin. Glass transition temperatures (Tgs) of the CEPHLs followed the behavior predicted by the Gordon-Taylor equation. Properties of the CEHPLs were independent of the original lignin source. The CEHPL copolymers were incorporated into lignin polyurethane networks (LPUs). The LPUs contained 17 to 43% lignin and showed a single Tg. Both the Tg and the Youngs modulus (MOE) of the LPUs were strongly correlated to the lignin content and type of diisocyanate used to prepare the network. Swelling studies indicated that the LPUs prepared from CEHPLs with a high MS (5-7) were not highly crosslinked networks. The LPU properties also appeared to be independent of the lignin source. In another set of experiments a HPL was separated into five fractions (F-HPLs) with molecular weights (MWs) between 1.5 and 10x10³ daltons. The Tg of the F-HPLs was correlated to molecular weight by the Fox-Flory equation. The fractionated HPLs were incorporated into polyurethane networks. The Tgs of these networks were related to the MW of the F-HPL. Swelling studies indicated that low molecular weight monofunctional fragments limited network formation. The LPUs were also used as one component in LPU/polymethyl methacrylate (PMA) interpenetrating polymer networks (IPNs). These IPNs varied in their LPU/PMMA composition and the presence of crosslinking. Dynamic mechanical and thermal analysis showed two phases in all of the IPNs. Mechanical properties were dependent on the IPN composition and phase crosslinking. For IPNs with a crosslinked LPU phase, the MOE values indicated the presence of dual phase continuity. A second series of IPNs was prepared to investigate the effects of lignin content on IPN properties. Phase separation appeared to be related to the lignin content. Mechanical properties were related to lignin content and not the phase behavior. / Ph. D.

Cette thèse porte sur la conception de carbonates cycliques originaux et d’amines dérivés des huiles végétales dans le but de synthétiser des poly(hydroxyuréthane)s entièrement bio-sourcés. D’une part, deux voies d’accès à des amines dérivées d’acides gras utilisant des conditions douces ont été étudiées. La première consiste en l’oxydation sous air d’alcools aliphatiques en nitriles en présence de TEMPO supporté sur silice, suivi par une hydrogénation des dinitriles en diamines. Egalement, des diènes dérivés d’acides gras ont été couplés à la cystéamine via une chimie thiol-ène, permettant l’accès à des diamines aliphatiques bio-sourcées. D’autre part, des carbonates cycliques substitués à 5 chaînons ont été synthétisés à partir de dérivés d’acides gras et de glycérol, dans le but d’augmenter leur réactivité vis-à-vis de l’aminolyse. En insérant un groupement fonctionnel éther, thio-éther ou ester en position α ou β des carbonates cycliques, la réactivité de ces derniers vis-à-vis des amines a pu être ajustée. L’étude de la sélectivité, des réactions secondaires et de la catalyse de la voie carbonate/amine a été menée afin de mieux appréhender cette voie d’accès à des polyuréthanes sans isocyanates. Des poly(hydroxyuréthane)s entièrement oléo-sourcés ont été synthétisés avec succès, montrant des propriétés physico-chimiques contrôlables selon la structure des monomères. / In this thesis, vegetable oils were used as a platform to design original cyclic carbonates and amines with the goal to synthesize fully bio-based poly(hydroxyurethane)s. On the one hand, two routes to fatty acid-based amines were implemented in mild conditions. First, the oxidation of aliphatic alcohols into nitriles was performed under air in the presence of supported TEMPO on silica, followed by hydrogenation of nitrile compounds into corresponding amines. Second, thiol-ene chemistry was performed on unsaturated fatty acid substrates to design original aliphatic bio-based diamines. On the other hand, substituted 5-membered cyclic carbonates were designed from fatty acids and glycerol derivatives to enhance their reactivity towards aminolysis. By inserting ether, thio-ether or ester functionalities in α- or β-position of the cyclic carbonates, their reactivity towards amines could be tuned. Investigations on the selectivity, side reactions and catalysis of the carbonate-amine reaction were carried out to apprehend this route to non-isocyanate polyurethanes. Fully vegetable oil-based PHUs with tunable physico-chemical properties with respect to the monomer structures could be easily achieved.

Thesis (PhD (Process Engineering))--University of Stellenbosch, 2006. / Existing thermoplastic polyurethanes (TPUs), used in the manufacturing of cardiovascular devices, still have unproven long-term biostability and may be prone to excessive plastic deformation when subjected to cyclic loading. These negative aspects can be attributed to, among other factors, the weak nature of virtual crosslinking through microphase separation. The modification and covalent crosslinking of existing medical grade polyurethanes with unsaturated acyl chlorides are thus proposed to improve these properties. A model compound study was used to find a suitable acyl chloride (4-pentenoyl chloride), confirm the intended carbamate nitrogen as successful reaction site and to optimize the chemistry of the reaction. Two medical grade polyurethanes, Pellethane® 2363- 80AE (Pellethane) and PurSil 35-80A (PurSil), were subsequently successfully modified with 4-pentenoyl chloride. The degree of modification could be accurately controlled (R2 = 0.99) to between 4.5% to 20.0% and between 11.5% to 18.5% for the respective polyurethanes. The degree of modification and method of crosslinking were then optimized to obtain the required mechanical properties (i.e. minimum hysteresis). The hysteresis and creep of the modified and crosslinked Pellethane were reduced by 42.5% and 44.0%, respectively, while the hysteresis of the modified and crosslinked PurSil was reduced by 12.9%. The chemical stability of Pellethane (control) modified Pellethane (15% modification) and crosslinked Pellethane (Pell15.0) was evaluated in an in vitro degradation study. The hysteresis of the crosslinked polymer was at least 27.5% better when compared to Pellethane, and showed a significant resistance to surface degradation (as studied with scanning electron microscopy). Although the soft phases in both polyurethanes are vulnerable toward degradation, it was not as pronounced in Pell15.0, mainly due to the restriction of chain movement resulting from the crosslinking. Small-diameter tubular constructs, with similar fiber and wall thicknesses, were electrospun from Pellethane and the 15% modified Pellethane. A standard electrospinning technique was used in the case of the former while in the case of the latter a novel “reactive” electrospinning technique was used for the in situ crosslinking of the novel material, while simultaneously forming the tubular constructs. It is suggested that the manufacturing of Pell15.0 be scaled up to produce adequate amounts of material to enable the extrusion and in vivo evaluation of e.g. pacemaker leads. A circulatory animal model, e.g. a senescent baboon model, could be used to evaluate and further optimize the electrospun tubular constructs.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Polyurethanes (PUs) are finding increasing application and use in many industries due to their advantageous properties, such as a wide range of flexibility combined with toughness, high chemical resistance, excellent weatherability, and very low temperature cure. PUs do however have some disadvantages, for instance, PU is considered an expensive polymer, especially when considered for solvent based adhesives. A motivation for this study was to consider a largely unstudied area of PU chemistry by combining PUs with polyacrylates. Polyacrylates are well known adhesives and can carry specific functionality, but have the disadvantage that their flexible backbones impart limited thermal stability and mechanical strength. In this study PU was incorporated into acrylates in an effort to obtain acrylate-g-urethanes with good properties. The mode of incorporation chosen was urethane macromonomers (UMs), a hardly mentioned substance in literature, yet one deserving investigation. UMs having different urethane chain lengths (X) were synthesized by the polyaddition polymerization of toluene diisocyanate (TDI) and ethylene glycol (EG) by the prepolymer method, which was terminated by 2-hydroxy ethyl methacrylate (HEMA) and isopropanol. The UMs were characterized by Fourier-transform infrared spectroscopy (FTIR), proton NMR (1H NMR), carbon NMR (13C NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Various percentages of the respective UMs (0-40 wt % according to acrylate monomers) were then incorporated into methyl methacrylate (MMA) and into normal butyl methacrylate (n-BMA) backbones via solution free radical copolymerization. The resulting methyl methacrylate-urethane graft copolymers (PMMA-g-urethane) and normal butyl methacrylate-urethane graft copolymers (n-PBMA-g-urethane) were characterized by GPC, 1H NMR and 13C NMR, FTIR, TGA, and DMA. Phase separation between the urethane segment and acrylate segment in the yield of graft copolymerization products was investigated by DMA and transmission electron microscopy (TEM). As the concentration of the UMs in the free radical copolymerization feed increased, lower yields of both graft copolymers PMMA-g-urethane and n-PBMA-g-urethane were observed and more UM was incorporated into the PMMA and n-PBMA backbones. It also was found that the thermal stability of the PMMA-g-urethane and n-PBMA-gurethane copolymers increased with increasing UM concentration. DMA results showed that in most graft copolymer products the two respective component parts of PMMA-g-urethane or n-PBMA-g-urethane were completely compatible as only one Tg was observed. Two glass transitions, at temperatures of 22.0 and 76.0 oC, corresponding to the n-PBMA and urethane moieties, were observed when the chain length of the UMs was increased from X=4 to X=32 [the amount of this UM used in the copolymerization feed was increased to 40%, and microphase separation was indicated].

O presente trabalho tem como intuito o estudo da reciclagem química de espumas rígidas de poliuretano através do processo de glicólise em um reator de micro-ondas utilizando o dietilenoglicol como agente decompositor, além de avaliar as propriedades de reaplicação e desempenho mecânico da espuma reciclada frente a uma espuma padrão de mercado. Uma fase de estudos preliminares foi estabelecida para avaliação comparativa entre catalisadores, considerando no estudo o hidróxido de sódio, o dilaurato de dibutil estanho e a dietanolamina, onde o hidróxido de sódio se mostrou como sendo o catalisador mais interessante para o escopo do trabalho. Para estudo das melhores condições reacionais, foi elaborado um desenho de experimentos avaliando as faixas ótimas para temperatura e concentração de catalisador utilizados no processo da glicólise onde foi constatada a temperatura de 230 °C e concentração de catalisador de 0,68% como valores mais adequados para a reciclagem. Os produtos da glicólise foram analisados quanto ao seu espectro no infravermelho e ressonância magnética nuclear de carbono-13, além de serem avaliados em relação ao seu número de hidroxila, basicidade e viscosidade. O conteúdo de polióis base de uma formulação de espuma rígida foi substituído por diferentes porcentagens de poliol reciclado sua reatividade e propriedades mecânicas como resistência à compressão e estabilidade dimensional foram analisados apontando um bom desempenho para os padrões de reatividade e propriedades mecânicas em uma substituição de até 40% dos polióis virgens pelo reciclado. / The present work has studied the chemical recycling of polyurethane rigid foams through microwave assisted glycolysis process using the diethyleneglycol as decomposing agent, and evaluating the reapplication and performance of the recycled foams in comparison to a market standard rigid foam. A preliminary study was set up to evaluate and compare the performance of catalysts such as sodium hydroxide, dibutiltin dilaurate and diethanolamine, where the sodium hydroxide presented the best overall performance. A design of experiments was performed in order to evaluate the optimum values of the processing temperature and catalyst concentration, which resulted in 230 °C and 0,68% as the optimum conditions to temperature and catalyst concentration, respectively. The glycolysis products were analyzed via infrared spectroscopy and carbon-13 nuclear magnetic resonance and were also evaluated regarding their hydroxyl number, basicity and viscosity. The base polyols from a standard rigid foam formulation were replaced by different amounts of recycled polyol and the reactivity profile as well as the physical properties such as the compression resistance and dimensional stability of the new formulations were measured pointing out a good performance of the reactivity profile and physical properties of the formulations with polyol replacement up to 40%.