京都大学 / 新制・課程博士 / 博士(理学) / 甲第23715号 / 理博第4805号 / 新制||理||1688(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 北川 宏, 教授 吉村 一良, 教授 竹腰 清乃理 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

abstract: The exceptional mechanical properties of polymers with heterogeneous structure, such as the high toughness of polyethylene and the excellent blast-protection capability of polyurea, are strongly related to their morphology and nanoscale structure. Different polymer microstructures, such as semicrystalline morphology and segregated nanophases, lead to coordinated molecular motions during deformation in order to preserve compatibility between the different material phases. To study molecular relaxation in polyethylene, a coarse-grained model of polyethylene was calibrated to match the local structural variable distributions sampled from supercooled atomistic melts. The coarse-grained model accurately reproduces structural properties, e.g., the local structure of both the amorphous and crystalline phases, and thermal properties, e.g., glass transition and melt temperatures, and dynamic properties: including the vastly different relaxation time scales of the amorphous and crystalline phases. A hybrid Monte Carlo routine was developed to generate realistic semicrystalline configurations of polyethylene. The generated systems accurately predict the activation energy of the alpha relaxation process within the crystalline phase. Furthermore, the models show that connectivity to long chain segments in the amorphous phase increases the energy barrier for chain slip within crystalline phase. This prediction can guide the development of tougher semicrystalline polymers by providing a fundamental understanding of how nanoscale morphology contributes to chain mobility. In a different study, the macroscopic shock response of polyurea, a phase segregated copolymer, was analyzed using density functional theory (DFT) molecular dynamics (MD) simulations and classical MD simulations. The two models predict the shock response consistently up to shock pressures of 15 GPa, beyond which the DFT-based simulations predict a softer response. From the DFT simulations, an analysis of bond scission was performed as a first step in developing a more fundamental understanding of how shock induced material transformations effect the shock response and pressure dependent strength of polyurea subjected to extreme shocks. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017

Ces travaux ont été réalisés dans le cadre d’un projet industriel avec l’entreprise Roxel visant à la substitution de la résine phénolique, impactée par la règlementation Reach, dans un matériau composite expansé : le Roxalte®. Ce matériau est composé d’un feutre de basalte imprégné de résine phénolique qui s’expanse sous l’effet de la température par l’action de microsphères expansibles contenu dans le mélange (Expancel®). Pour s’adapter aux différentes utilisations du Roxalte®, des systèmes époxy répondant aux exigences de Reach ont été sélectionnés. Le premier objectif de cette thèse est la substitution de la résine phénolique. Le second objectif est de fournir une méthodologie pour la réalisation de mousses. La caractérisation physicochimique de la résine phénolique ainsi qu’une étude des relations structure/propriétés ont orienté la sélection vers un système faisant état de très hautes Tg : le Tris(4-hydroxyphenyl) methane triglycidyl ether (TETM) allié au durcisseur amine diaminodiphénylsulfone (DDS). La solution de remplacement immédiate a alors consisté à utiliser le système époxy [TETM/DDS] ainsi qu’un grade d’Expancel® adapté à l’intervalle de polymérisation de la résine. L’optimisation du cycle de réticulation a permis d’atteindre une Tg égale à 330 °C. La seconde étape a consisté à optimiser le moussage en calant la cinétique de réticulation sur la cinétique d’expansion par la détermination des temps de gel du système époxy et des temps d’expansion des microsphères. En dernier lieu, le composite expansé a été mis en œuvre grâce à l’ajout de solvant non réactif (acétone). Le deuxième volet de ces travaux a porté sur l’étude du moussage en utilisant le bicarbonate de sodium (BS) comme agent gonflant. La dualité exothermique/endothermique du procédé (exothermie de la réticulation et endothermie de la décomposition du BS) a été étudiée. Des suivis cinétique en mode isothermes et anisotermes ont été réalisés sur deux systèmes époxy (TETM/DDS et TETM/IPDA), sur le BS et sur les mélanges TETM/DDS+BS et TETM/IPDA+BS. L’ajout de fibres de basalte a fait état de différence notable sur la morphologie des mousses à base des systèmes époxy et du BS et les phénomènes de coalescence des bulles et de diffusion du gaz ont été mis en évidence. Une meilleure répartition des fibres et des bulles avec le système [TETM/IPDA] a été observé. / This work was performed within the framework of an industrial project of Roxel company. The project aim was the substitution of phenolic resin in an expanded composite material: the Roxalte®. This material is made of basalt mat impregnated by phenolic resin which expands under heating by the action of expandable microspheres (Expancel®). The second objective of this work is to provide a methodology for foaming optimization. REACH compliant epoxy resins were selected as substitute. Our choice was guided by the physical-chemical characterization of phenolic resin and the study of structure-property relationship. A high glass transition temperature system has been selected: the Tris(4-hydroxyphenyl)methane triglycidyl ether (TETM) with amine hardener diaminodiphenylsulfone (DDS). The immediate alternative solution consisted of epoxy system [TETM/DDS] and appropriate Expancel® microspheres. The microspheres have been chosen according to the curing temperature interval of the resin. The curing process optimization has been achieved and a Tg equal to 330 °C has been reached. Then the temperature that leads to equilibrium between the microsphere’s foaming kinetic and the resin gelation kinetic has been determined. The second part of this work deals with the study of foaming process using sodium bicarbonate (SB) as foaming agent. The exothermic-endothermic duality of the process (exothermicity of polymerization and endothermicity of SB decomposition) has been studied. Reaction kinetics of epoxy resins (TETM/DDS and TETM/IPDA), SB and mixes (TETM/DDS+BS and TETM/IPDA+BS) have been followed in isothermal and non-isothermal modes. Morphologies differences between TETM/DDS+BS and TETM/IPDA+BS systems and coalescence and diffusion phenomena have been observed when basalt fibers was added. Improved fibers distribution in TETM/IPDA system have been revealed.

Physically assembled gels are widely applicable in the food industry, biomedical devices, drug delivery, and soft robotics due to their tunable mechanical properties and thermoreversibility. The mechanical responses of these gels originate from their microstructure. Therefore, factors affecting the gel microstructure like polymer molecular weight, solvent quality, and polymer concentration play a significant role in determining their mechanical behavior. Gel microstructure also changes during the deformations resulting in a deviation from the structure-property relationship established for the low deformations. During large deformations, other factors like stress relaxation, poroelasticity, and polymer chain entanglement contribute significantly to the gel response. This complexity extends to the understanding of their failure behavior that occurs at large deformations. The low strain mechanical behavior of gels is governed by load-bearing chain density. They are often represented with non-linear elastic models, which ignore the contribution from viscous dissipation, polymer entanglements, surface tension, and bond dissociation. In addition, the available theoretical models cannot capture the experimental conditions like boundary confinement, therefore, numerical simulations are useful to test the developed model by comparing with experimental observations. With this objective, the present dissertation is focused on understanding the failure of physically assembled gels that consists of an ABA-type triblock copolymer dissolved in a B-block (midblock) selective solvent. Here, gelation occurs as a result of relative difference in the solubility of A-blocks (endblocks) and B-blocks (midblocks) with solvent. The thermo-mechanical characterization of these gels was performed using rheology, cavitation rheology, and DSC. A custom-built experimental set-up was developed to conduct large deformation experiments like tensile tests, creep failure experiments, and fracture experiments with a predefined crack. To characterize the gel microstructure, small-angle x-ray/neutron techniques were used. A change in the gel microstructure during deformation was also captured. The microstructure of gels was tuned by varying temperature, polymer volume fraction, midblock length, and by addition of midblock homopolymer. Finite element simulations have been used to understand the effect of boundary confinement, surface tension, and viscous dissipation. The present work provides a better understanding of failure behavior in physically assembled gels through the polymer dynamics at nano-scale level.

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Low molecular weight liquid polybutadienes (1000 – 2000 g/mol) consisting of 60 mol% 1,2-polybutadiene repeating units were synthesized via anionic telomerization and conventional anionic polymerization. Maintaining the initiation and reaction temperature less than 70 °C minimized chain transfer and enabled the telomerization to occur in a living fashion, which resulted in well-controlled molecular weights and narrow polydispersity indices. MALDI-TOF mass spectrometry confirmed that the liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. Subsequently, 2-ureido-4[1H]-pyrimidone (UPy) quadruple hydrogen-bonding was introduced to telechelic poly(ethylene-co-propylene), and mechanical characterization of the composites with UPy-functionalized carbon nanotubes was performed. The composites enhanced the mechanical properties and the UPy-UPy association between the matrix polymer and carbon nanotubes prevented the decrease of an elongation at break. The matrix polymer was also reinforced without sacrificing the processability. Additionally, UPy groups were introduced to styrene-butadiene rubbers (SBRs). Introducing UPy groups to SBRs drastically changed the physical properties of these materials. Specifically, the SCMHB networks served as mechanically effective crosslinks, which raised Tg and enhanced the mechanical performance of the SBRs. Novel site-specific sulfonated graft copolymers, poly(methyl methacrylate)-g-(poly(sulfonic acid styrene)-b-poly(tert-butyl styrene)), poly(methyl methacrylate)-g-(poly(tert-butyl styrene)-b-poly(sulfonic acid styrene)), and the corresponding sodium sulfonate salts were successfully synthesized via living anionic polymerization, free radical graft copolymerization, and post-sulfonation strategies. The graft copolymers contained approximately 9 – 10 branches on average and 4 wt% of sulfonic acid or sodium sulfonate blocks adjacent to the backbone or at the branch terminus. The mobility of the sulfonated blocks located at the branch termini enabled the sulfonated blocks to more readily interact and form ionic aggregates. The glass transition temperatures (Tg) of the sulfonated graft copolymers with sulfonated blocks at the branch termini were higher than that of copolymers with sulfonated blocks adjacent to the backbone. More facile aggregation of sulfonated blocks at the branch termini resulted in the appearance of ionomer peaks in SAXS whereas ionomer peaks were not observed in sulfonated graft copolymers with sulfonated blocks adjacent to the backbone. In addition, similar analogues, novel site-specific sulfonated graft copolymers, poly(methyl methacrylate)-g-(poly(sulfonic acid styrene)-b-poly(ethylene-co-propylene)) (PMMA-g-SPS-b-PEP), poly(methyl methacrylate)-g-(poly(ethylene-co-propylene)-b-poly(sulfonic acid styrene)) (PMMA-g-PEP-b-SPS), and the corresponding sodium sulfonate salts were successfully synthesized. Estimated ï £N values predicted the phase separation of each block and differential scanning calorimetry (DSC) and dynamic mechanical analysis confirmed the phase separation of each block component of the graft copolymers. The aggregation of sulfonic acid or sodium sulfonate groups at the branch termini restricted the glass transition of the PEP block. This lack of the glass transition of the PEP block resulted in higher storage modulus than a sulfonated graft copolymer with sulfonated blocks adjacent to the backbone. The location of sulfonated blocks in both sulfonic acid and sodium sulfonate graft copolymers significantly affected the thermal, mechanical and morphological properties. Lastly, symmetric (16000 g/mol for each block) and asymmetric (14000 g/mol and 10000 g/mol for each block) poly(ethylene-co-propylene)-b-poly(dimehtylsiloxane) (PEP-b-PDMS) were synthesized using living anionic polymerization and subsequent hydrogenation. The onset of thermal degradation for the PEP-b-PDMS diblock copolymer was higher than 300 ºC and PEP-b-PDMS was more thermally stable than the precursor diblock copolymer, polyisoprene-b-PDMS. DSC analysis of PEP-b-PDMS provided Tg of PDMS -125 ºC, Tg of PEP -60 ºC, Tc of PDMS -90 ºC, and Tm of PDMS -46 and -38 ºC, respectively. Appearance of thermal transitions of each PEP and PDMS block revealed the formation of phase separation. Estimated Ï N also supported the phase separation. / Ph. D.

Polyimides are frequently used as insulating layers in the microelectronics industry. These polymers are tough, have high thermal stability, and have favorable dielectric properties; consequently, polyimides are excellent materials for insulating layers in microelectronic devices. In this research, self-assembled monolayers are investigated for use as an adhesion promoter for metal substrates, and for corrosion protectors of the metal surface. Gold substrates modified by adsorption of 3- and 4-aminothiophenol monolayers, 3- and (4-mercaptophenyl) phthalimide (MPP) monolayers, and by reaction of the 3- and 4-aminothiophenol monolayers with the phthalic anhydride were studied using reflection absorption infrared spectroscopy, contact angle measurement, ellipsometry, and electrochemical measurements. Reactions on the monolayers are used to model the attachment of an insulating polyimide to the substrate. The covalent attachment of the anhydride is confirmed, and the efficiency of the reaction of the aminothiolphenol monolayers is investigated. The reactivity of the aminothiolphenol monolayers is found to depend on the position of the amino-group around the phenyl ring. Impedance spectroscopy is used to investigate the ionic insulating properties of these systems. The 4-mercaptophthalimide monolayer is found to have the highest monolayer resistance to ion transport. This result suggests that it forms the most densely packed monolayer. The monolayer resistance of the surfaces prepared by adsorption of the aminothiolphenol isomers followed by reaction with phthalic anhydride is much lower than the corresponding deposited mercaptophthalimide monolayers. These results suggest that the reaction efficiency is low. Impedance spectroscopy and polarization measurements suggests a higher protection efficiency for 3-mercaptophenylphthalimide. These results will be discussed in the context of the ability of the isomeric mercaptophthalimide monolayers to serve as protectors against substrate corrosion. / Ph. D.

The focus of this dissertation was to investigate the influence of sidechain structure and sidechain content on the morphology and physical properties of perfluorosulfonic acid ionomer (PFSA) membranes. One of the primary objectives was to characterize the thermomechanical relaxations for short sidechain PFSAs developed by 3M and Solvay, as well as a new multi-acid sidechain perfluoroimide acid ionomer (PFIA) from 3M. Partial neutralization experiments played a key role in systematically manipulating the strength of the electrostatic interactions between proton exchange groups on each sidechain, leading to the elucidation of the molecular-level motions associated with multiple thermal relaxations observed by dynamic mechanical analysis (DMA). Particularly, 3M PFSA and Solvay Aquivion lack an observable β-relaxation in the sulfonic acid-form that is observed in the long sidechain PFSA, Nafion. By varying the strength of the physically-crosslinked network through exchanging the proton on the sulfonic acid groups for large counterions, we were able to conclude that the shorter sidechain length and increase in ion content in the 3M PFSA and Solvay Aquivion serves to restrict the mobility of the polymer backbone such that the onset of segmental motions of the main chains is not observed at temperatures below the α-relaxation temperature, where destabilization of the physically crosslinked network occurs. As a complementary technique to DMA for probing the relaxations in PFSAs, we introduced a new pretreatment method for differential scanning calorimetry (DSC) measurements that uncover a thermal transition in H+-form 3M PFSA, Aquivion, and Nafion membranes. This thermal transition was determined to be of the same molecular origin as the dynamic mechanical α-relaxation temperature in H+-form PFSAs, and the β-relaxation temperature in tetrabutylammonium (TBA+)-form PFSAs. The thermomechanical relaxations in multi-acid sidechain 3M PFIA were also investigated. Interestingly, the additional acidic site on PFIA led to unexpected differences in thermal and mechanical properties, including the appearance of a distinct glass transition temperature otherwise not seen in PFSA ionomers. We utilized small-angle X-ray scattering (SAXS) studies to probe the differences in aggregate structure between the PFIA and PFSA membranes in order to uncover the morphological origin of the anomalous thermomechanical behavior in PFIA membranes. Larger aggregate structures for PFIA, compared to PFSA, incorporate intervening fluorocarbon chains within the aggregate, resulting in increased spacing between ions that reduce the collective electrostatic interactions between ions such that the onset of chain mobility occurs at lower temperatures than the α-relaxation for PFSA. The SAXS profiles of PFSAs showed two scattering features resulting from scattering between crystalline domains and ionic domains distributed throughout the polymer matrix. In order to fit the "ionomer peak" to models used for the PFIA and PFSA aggregate structure determination, we presented a method of varying the electron density of the ionic domains by using different alkali metal counterions as a tool to make the intercrystalline feature indistinguishable. This allows for isolation of the ionomer peak for better fits to scattering models without any interference from the intercrystalline peak. Lastly, an investigation of annealing PFSAs of different sidechain structures in the tetramethylammonium (TMA+) counterion form above their α-relaxation showed a profound crystalline-like ordering of the TMA+ counterions within the ionic domains. This ordering is maintained after reacidification and leads to improved proton conductivity, which indicates that this method can be used as a simple processing method for obtaining improved morphologies in proton exchange membranes for fuel cell applications. / Doctor of Philosophy / Hydrogen fuel cells offer an environmentally friendly, high efficiency method for powering vehicles, buildings, and portable electronic devices. At the center of a hydrogen fuel cell is a polymer membrane that contains ionic functionalities, which conduct hydrogen ions (protons) from the anode to the cathode while preventing conduction of electrons. The electrons travel through an external circuit to produce electricity, while the protons travel through the polymer membrane and meet with oxygen on the other side to produce water, the only byproduct of a hydrogen fuel cell. The efficiency of this process relies on the ability of the polymer membrane to conduct protons, and the lifetime of a fuel cell depends on the mechanical stability of this membrane. Perfluorosulfonic acid ionomers are good candidates for use as polymer membranes in hydrogen fuel cells due to their Teflon backbone that provides mechanical stability and their sulfonic acid functionalities that form channels for proton conduction. In this work, we probe the structure-property relationships of different perfluorosulfonic acid ionomers for use as fuel cell membranes. We focus on thermal analysis techniques to develop a fundamental understanding of the effect of chemical structure and sulfonic acid content on the temperature-induced mobility of the polymer chains in these ionomers. This mobility at elevated temperatures can be utilized to rearrange the morphological structure of perfluorosulfonic acid ionomer membranes in order to enhance proton conductivity and mechanical integrity.

A series of random and amorphous copolyesters containing different cycloaliphatic rings within the polymer chains were prepared by melt polycondensaton of difunctional monomers (diesters and diols) in the presence of a catalyst. These polyesters were characterized by nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tensile tests and/or dynamic mechanical analysis (DMA). The copolyester based on dimethyl bicyclo[2.2.2]octane-1,4-dicarboxylate (DMCD-2) was observed to have a higher Tg, about 115ºC, than the other copolyesters with the same compositions in this study. For copolyesters containing different compositions of dimethyl-1,4-cyclohexane dicarboxylate (DMCD) and DMCD-2, the Tg increased linearly with the increase of DMCD-2 mole content. DMA showed that all of the cycloaliphatic copolyesters had secondary relaxations, resulting from conformational transitions of the cyclohexylene rings. The polyester based on DMCD-3 in the hydrolytic tests underwent the fastest hydrolytic degradation among these samples. A new triptycene diol (TD) was synthesized and incorporated into a series of cycloaliphatic copolyester backbones by melt condensation polymerization. Straight chain aliphatic spacers, including ethylene glycol (EG), 1,4-butanediol (BD) and 1,6-hexanediol (HD), were used as co-diols to explore their effects on polyester properties. An analogous series of non-triptycene copolyesters based on various hydroxyethylated bisphenols were also prepared for comparison. The results revealed that the TD-containing polymers had higher thermal stability and higher Tg's than the corresponding non-TD analogs. For TD-containing copolyesters, the mechanical properties were found to be dependent on the types and compositions of the co-diols. A 1,4-butanediol-based triptycene copolyester was observed to have a significantly increased Tg and modulus while maintaining high elongation at ambient temperature. Furthermore, it was demonstrated that the triptycene polyester exhibited higher Tg and modulus than those containing bisphenol derivatives. However, all of the 1,4-butanediol based copolyesters were brittle and had comparable moduli at low temperatures (-25°C or -40 °C). Melt polycondensation was also used to prepare a series of all-aliphatic block and random copolyesters including the following aliphatic monomers: trans-DMCD, DMCD-2, neopentyl glycol (NPG), diethylene glycol (DEG) and dimethyl succinate (DMS). The polymer compositions were determined by 1H NMR, and the molecular weights were determined using SEC. The polyesters were also characterized by TGA, DSC, DMA and tensile tests. Phase separation was not observed in these block copolyesters. However, the block copolyester containing DMCD-2 and NPG was observed to have a higher Tg than the block copolyester based on trans-DMCD and NPG. In addition, these block copolyesters were found to have better mechanical properties than the corresponding random copolyesters. / Ph. D.