No description available.

Yes / Orientation direction dependency of whitening activated at large strains was studied using four pre-oriented isotactic polypropylene (iPP) samples with different molecular weights stretched along different directions with respect to the pre-orientation (0°, 45°, and 90°) by means of in situ wide-, small-, and ultra-small-angle X-ray scattering techniques. A macroscopic fracture of iPP materials was also observed following the stress whitening at large strains. These two associated processes in pre-oriented iPP samples at elevated temperatures were found to be governed by not only the molecular weight of iPP but also the pre-orientation direction. For a certain pre-orientation direction of iPP, both the critical stress of cavitation induced-whitening and failure stress increased with increasing molecular weight. For one given molecular weight, the pre-oriented iPP showed the smallest critical stress for whitening and failure stress along the pre-orientation direction (0°) while the samples displayed larger values for the same behaviors when stretched at 45° or 90° with respect to the pre-orientation direction. Such behavior suggested that oriented amorphous networks, with different mechanical strengths, can be generated during the second deformation processes in these pre-oriented iPP samples. The evolution of inter-fibrillar tie chains in highly oriented amorphous networks was considered as the main factor controlling the response of the inner network to the external stress since the cavitation-induced whitening activated at large strains was caused by the failure of load bearing inter-fibrillar tie chains in the oriented amorphous network.

Biodegradable polyesters represent a class of extremely useful polymeric materials for many applications. Among these polyesters, the biodegradable and biocompatible, polylactide is very promising for many applications in both medical and industrial areas. Other biodegradable polymers such as polytrimethylene carbonate, polybutyrolactone, polyvalerolactone, and polycaprolactone can be blended or copolymerized with polylactide to fine tune the properties to fit the needs for their applications. The properties of these polymers and copolymers depend upon the tacticity of the polymers which can be directly controlled by the catalysts used for polymer production. Therefore, it has been of great interest to develop new selective catalytic systems for the ring-opening polymerization of lactide and other cyclic monomers. This dissertation focuses on developing new zinc and aluminum complexes and studying their selectivity and reactivity of these complexes for the ring-opening polymerization of lactide and other cyclic monomers, i.e. trimethylene carbonate, beta-butyrolactone, delta-valerolactone, and epsilon-caprolactone. Herein, aspects of the ring-opening polymerization of lactide and other cyclic monomers utilizing novel zinc and aluminum complexes will be discussed in detail. In the process for the ring-opening polymerization of lactide, chiral zinc half-salen complexes derived from natural amino acids have shown to be very active catalysts for producing polymers with high molecular weight and narrow polydispersities at ambient temperature. The chiral zinc complexes were found to catalyze rac-lactide to heterotactic polylactides with Pr values ranging from 0.68-0.89, depending on the catalyst and reaction temperature employed during the polymerization process. The reactivities of the various catalysts were greatly affected by substituents on the Schiff base ligands, with sterically bulky substituents being rate-enhancing. Furthermore, a series of both chiral and achiral aluminium half-salen complexes have been synthesized and characterized. These aluminum complexes all showed moderate selectivity to the ring-opening polymerization of rac-lactide to produce isotactic polylactide with Pm value up to 0.82 in toluene at 70 degrees C. Moreover, some of the studied aluminum complexes displayed epimerization of rac-lactide to meso-lactide during the polymerization process. Kinetic studies for the ring-opening polymerization of lactide utilizing these zinc and aluminum complexes are included in this dissertation. Along with these studies, the copolymerization of lactide with epsilon-caprolactone and delta-valerolactone will also be presented.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16879号 / 工博第3600号 / 新制||工||1544(附属図書館) / 29554 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 金谷 利治, 教授 長谷川 博一, 教授 辻井 敬亘 / 学位規則第4条第1項該当

Orientador: Maria do Carmo Gonçalves / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-05T22:42:32Z (GMT). No. of bitstreams: 1 Valter_SilvanadaSilva_M.pdf: 2873175 bytes, checksum: b6a093f5fd737b7919417a5e55da89da (MD5) Previous issue date: 2005 / Resumo: Neste trabalho foram estudadas blendas cristalinas de poli(1-buteno) com o copolímero de poli(propileno-co-1-buteno-co-etileno). A influência do tempo de envelhecimento nas características estruturais e nas propriedades térmicas e mecânicas do iPB puro e das blendas de iPB/copolímero foram estudados por difratometria de raios X, termogravimetria (TG), calorimetria diferencial de varredura (DSC) e análise dinâmico-mecânica (DMA). O efeito da adição de copolímero e das condições de cristalização sobre a morfologia dos cristais de iPB foi avaliada por microscopia óptica (MO) e por microscopia de força atômica com modo de força pulsada digital (DPFM). A estabilidade térmica apresentada pelas blendas de iPB/copolímero foi similar à dos polímeros puros. O iPB recém-preparado apresentou cristais de forma II que foram transformados em cristais termodinamicamente estáveis de forma I com o envelhecimento à temperatura ambiente. O grau de cristalinidade obtido para os cristais de forma II e I não foi alterado com a adição de copolímero. Porém, o módulo de armazenamento aumentou com o tempo de envelhecimento e reduziu com o aumento da concentração de copolímero. O iPB apresentou morfologia esferulítica nas diferentes condições de cristalização utilizadas, porém a temperatura de cristalização afetou a densidade de núcleos e a taxa de cristalização. As técnicas microscópicas evidenciaram a segregação do copolímero entre os feixes de lamelas e entre os esferulitos de iPB. Em blendas com concentração superior a 30% de copolímero foram identificados domínios de segregação de fases no estado fundido e que o processo de cristalização ocorreu a partir de nucleação heterogênea. Foi também observado que a transição cristalina do iPB alterou a morfologia das blendas, promovendo a distribuição mais uniforme dos domínios da fase amorfa entre os cristais de iPB. Os parâmetros de Avrami calculados confirmaram a formação de estruturas esferulíticas e a sobreposição de nucleação primária e secundária com o crescimento dos esferulitos. Concluindo, o conjunto de resultados obtidos permite propor que blendas de iPB/poli(propileno-co-1-buteno-co-etileno) apresentaram miscibilidade parcial em concentrações de copolímero inferiores à 20% e imiscibilidade em concentrações mais altas. / Abstract: In this work crystalline blends of isotactic poly(1-butene) and poly(propylene-co-1-butene-co-ethylene) copolymer has been studied. The effect of aging time on the structural and thermal characteristics of these blends has been investigated by X-ray diffraction, thermogravimetry (TG), differencial scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The effect of the addition of copolymer as well as the crystallization conditions on the morphology of iPB crystals was evaluated by polarized light microscopy (OM) and atomic force microscopy in digital pulsed force mode (DPFM). The thermal stability presented by the blends of iPB/copolymer was closed to that one of the pure copolymer. The as-crystallized iPB sample showed crystals of the kinetically favored tetragonal form II, which were transformed to the stable hexagonal crystalline form I with increasing aging time at room temperature. The degree of crystallinity for form II crystals did not change with the addition of the copolymer. However, storage modulus was increased with the increase of the aging time and decreased with the increase of the copolymer concentration. The iPB samples presented spherulitic morphology for different crystallization conditions, however, the crystallization temperature affected the nucleus density and crystallization rate. The microscopic techniques demonstrated that the copolymer segregation occurred between iPB crystalline lamellae and at the interspherulitic regions. In blends containing copolymer concentration higher than 30wt% it were identified phase segregation domains in the melt state and that the crystallization process occurred through heterogeneous nucleation. It was also observed that the iPB crystalline transformation changed the blend morphology, promoting a more uniform distribution of amorphous phase domains in the iPB crystals. The Avrami parameters calculated confirmed the formation of spherulitic structures and the combination of primary and secondary nucleation during the spherulite growing. Based on the obtained results, it is proposed that the iPB/ poly(propylene-co-1-butene-co-ethylene) blends presented partial miscibility at copolymer concentration lower than 20% and immiscibility at higher copolymer concentrations. / Mestrado / Físico-Química / Mestre em Química

No description available.

Yes / Cavitation is an important phenomenon in solid-phase deformation of polymers, which either has potential adverse effects on physical properties or creates potential opportunities for new properties. In either case, it needs to be better understood to help achieve better control of cavitation and its effects. Cavitation associated with solid-phase deformation in a β-nucleated isotactic polypropylene was found to depend on the solid-phase deformation route employed. Compared with samples obtained by free tensile stretching, cavitation was suppressed in samples deformed via die-drawing, although an almost identical β-to α-phase transition was observed for both deformation routes. Even when die-drawn samples were subsequently deformed to large strains by free stretching, there was still no comparable cavitation compared with the single free tensile-stretching route. The die-drawing process appears to suppress cavitation by fundamentally diminishing the number of growable nuclei of cavities, rather than merely hindering the growth of cavities. A relationship between cavitation intensity and the fractions of lamellae along specific directions has been established. During subsequent free stretching of die-drawn samples, newly created cavities were suggested to be initiated within the crystalline layers. The reduction of the cavity nuclei in the die-drawing process originated from the stabilization of the connections between the crystalline blocks within the lamellae. / This work is supported by the National Natural Science Foundation of China (21704102 and 51525305), Newton Advanced Fellowship of the Royal Society, United Kingdom (NA 150222) and ExxonMobil.

Yes / The morphology distribution of isotactic-polypropylene (iPP) shaped through a die during hot stretching process was investigated via wide-angle X-ray diffraction technique. The evolution of micro-structures in the outer layer (layer closer to the die wall) and the inner layer (layer in the center of die) of die-drawn iPP were both recorded. It turned out that the difference of morphology distribution between outer and inner layers changes with the distance from the die entrance to exit. In general, a larger difference between outer and inner layers could be found at the intermediate deformation region inside the die while such difference disappeared at both of the entrance and exit regions of die. These behaviors could be interpreted as a result of the existence of a heterogeneous distribution of force field inside the die, which was caused by the die geometry and inclination of the drawing force. This work showed that the heterogeneous force field inside the die could be revealed through analyzing the morphology of a die-drawn sample.

Yes / The isotactic polypropylene (iPP) usually shows a unique parent-daughter lamellae structure in which the parent and daughter lamellae are against each other with a near perpendicular angle (80° or 100°). Inducing a high fraction of oriented cross-hatched structure in iPP during processing is desirable for designing the bi-oriented iPP products. We processed a commercial iPP via tensile-stretching and die-drawing to evaluate the structural evolution of oriented parent-daughter lamellae. It turned out that the die-drawing process had an advantage in attaining a high fraction of oriented cross-hatched structure of iPP, as compared to the free tensile stretching. Besides, the presence of α-nucleating agents affected the formation of oriented parent-daughter lamellae in the die-drawn samples whereas such influence diminished in the free stretched ones. It was found that the confined deformation inside the die led to the well-preserved oriented cross-hatched structure in the die-drawn iPP. / This work was financially supported by the National Natural Science Foundation of China (Nos. 21704102, U1832186, and 51525305), Newton Advanced Fellowship of the Royal Society, United Kingdom (No. NA150222) and ExxonMobil Asia Pacific Research & Development Co., Ltd.

Yes / The structural formation and development of isotactic polypropylene (iPP) upon the micro-injection molding process was investigated at different mold temperatures and molecular weights utilizing a real-time synchrotron radiation small angle X-ray scattering (SAXS) technique combined with a customized micro-injection molding apparatus. Shish-kebab structure and parent-daughter lamellae were found to be formed during micro-injection molding for all iPP samples. In the case of kebab lamellae, a considerable growth in the long period and in the average thickness of lamellar crystallites and amorphous domains is observed at initial stages of crystallization for samples molded at varying temperatures. This effect is caused by the successive formation of thin lamellae in the outer layer and thick lamellae in the inner layer during the manufacturing process as evidenced by the spatial distribution of the crystalline lamellae across the thickness. In addition, the length of the shish formation increases remarkably at the onset of crystallization, the extent of which is dependent on the mold temperature. Despite the large changes of the lamellar stacks and the shish misorientation, the final length of the shish remains essentially unchanged when varying mold temperature. Since there is a critical orientation molecular weight above which the chains are stretched and oriented to form stable shish, the iPP sample with a low molar mass exhibits an overall decrease in the scattering intensity of SAXS patterns compared to the high molecular weight polypropylene. / This work is financially sponsored by the National Key R&D Program of China (2018YFB0704200), National Natural Science Foundation of China (21674119, 21790342 and 51525305), and Royal Society Newton Advanced Fellowship, United Kingdom (NA150222).