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International audience; In the present work, we propose the synthesis of a new family of sugar derived 1,4:3,6-dianhydrohexitol based AA/AB-type monomers. Unprecedented diacids based on Isomannide and Isoidide were elaborated with high yields and showed interestingly high melting point ranges (240-375 degrees C). Optimization of reaction conditions (temperature, time of reaction, and reactant ratios) has been investigated to synthesize the key intermediate of a set of AB monomers with acid, ester, and acid chloride functionalities. Isosorbide based ether benzoic acid AB monomer was polymerized and characterized by NMR and DSC techniques. The results show a semicrystalline behavior of the obtained polymer thanks to the controlled stereoregular arrangement of the AB starting monomer.

The replacement of metals with polymer-based materials is considered to be key to reducing weight, cost, and cycle times in different technological applications, including the automotive and aerospace industries. Semiaromatic polyamides are particularly attractive engineering polymers due to their balanced mechanical properties and processability. They combine high strength and stiffness due to the rigid aromatic repeating units with greater ductility and better processability than those of polyaramids, owing to the presence of flexible aliphatic repeating units. However, the challenge remains to find ways to improve the strain at break and toughness of semiaromatic polyamides and their composites, without inducing adverse consequences for their strength and stiffness. The present thesis addresses this challenge following two complementary approaches. In an engineering-driven approach suitable to industrial scale-up, we produced random copolyamides by high-temperature melt-blending of a strong and stiff semiaromatic polyamide with more ductile aliphatic polyamides. The blending of up to 30 wt% of PA66 or PA610 in PA6TI resulted in a five-fold increase of the strain at break compared to that of pure PA6TI, with almost no change in stiffness and only minor losses in strength. In a second, chemistry-driven approach inspired by the crucial role of polymer chain in silk materials, we designed and synthesized monomers that induce the formation of U-turn folds€ in attempt to induce re-entrant chain folding in the crystalline lamellae of semiaromatic polyamides. Contrary to polyamides with kinked repeating units that are usually amorphous, the use of such monomers did not impede crystallization. Acridine-based polyamides were shown to adopt a folded structure in the solid state that was structurally related to the beta-serpentine folds in amyloids. They also exhibited a modulus comparable to other semiaromatic polyamides and were harder and stiffer than the structurally related anthracene-based polymers that did not show chain folding due to steric repulsion in the required conformation.

A waterborne latex-based technique, in which functionalized laponite is attached to PS and acrylic latex particles, is used to prepare films containing up to 50 wt% laponite. At high laponite contents this leads to a cellular arrangement of the laponite-rich layers, concentrated at the latex particle interfaces. MDSC shows that a significant proportion of the organic matrix does not contribute to the glass transition. However, this "rigid" matrix fraction arises from intercalation of the laponite stacks, and cannot account for the large increases in global stiffness in the rubbery state (T> T g) on laponite addition. The mechanical response for T> T g is therefore discussed in terms of a four-phase structure, in which the intercalated laponite stacks embedded in a matrix with a relatively high rubbery modulus form a cellular structure, which is in turn embedded in a matrix whose modulus is closer to that of the bulk polymer. The importance of the cellular arrangement is underlined by the much lower rubbery modulus observed by DMA in specimens produced by deforming the original films in plane strain compression to produce oriented textures with relatively little connectivity between the laponite-rich layers. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

A cis-poly(phenylene vinylene) (cis-PPV) recently synthesized by Katayama, Ozawa, and coworkers undergoes photo-isomerization into trans configuration. This isomerization occurred rather quickly within 45 min in solvent-cast films at room temperature. The cis-PPV chains exhibiting this quick isomerization were expected to be highly mobile in the bulk state, and this expectation was examined from thermal, structural, and viscoelastic tests for a cis-PPV sample with Mn=4300 and Mw/Mn=2.16. It turned out that the as-polymerized cis-PPV was partially crystalline and fully melted at Tm≅109 °C. The samples quenched from a molten state to lower temperatures (≤70°C

New and promising treatments for coronary heart disease are enabled by vascular scaffolds made of poly(L-lactic acid) (PLLA), as demonstrated by Abbott Vascular’s bioresorbable vascular scaffold. PLLA is a semicrystalline polymer whose degree of crystallinity and crystalline microstructure depend on the thermal and deformation history during processing. In turn, the semicrystalline morphology determines scaffold strength and biodegradation time. However, spatially-resolved information about the resulting material structure (crystallinity and crystal orientation) is needed to interpret in vivo observations. The first manufacturing step of the scaffold is tube expansion in a process similar to injection blow molding. Spatial uniformity of the tube microstructure is essential for the consistent production and performance of the final scaffold. For implantation into the artery, solid-state deformation below the glass transition temperature is imposed on a laser-cut subassembly to crimp it into a small diameter. Regions of localized strain during crimping are implicated in deployment behavior. To examine the semicrystalline microstructure development of the scaffold, we employed complementary techniques of scanning electron and polarized light microscopy, wide-angle X-ray scattering, and X-ray microdiffraction. These techniques enabled us to assess the microstructure at the micro and nano length scale. The results show that the expanded tube is very uniform in the azimuthal and axial directions and that radial variations are more pronounced. The crimping step dramatically changes the microstructure of the subassembly by imposing extreme elongation and compression. Spatial information on the degree and direction of chain orientation from X-ray microdiffraction data gives insight into the mechanism by which the PLLA dissipates the stresses during crimping, without fracture. Finally, analysis of the microstructure after deployment shows that it is inherited from the crimping step and contributes to the scaffold’s successful implantation in vivo.

We present results from molecular dynamics simulations for an all-atoms model of a semicrystalline polyethylene under uniaxial tensile test. Our model has a realistic semicrystalline organization of two high molecular chains which are involved in two crystalline and two amorphous phases. The tie-molecules link these phases. A high content of tie-molecules is compatible with the stability of the semicrystalline organizations in the initial state. The main objective of the study is to check the effect of some molecular parameters, poorly known from experiments, on the mechanical properties under uniaxial tensile test. It is a way to have an insight on the value of the probable molecular parameters. We show that the number of tie-molecules mainly acts on the elastic modulus and the lamellar thickness acts on the yield stress. A nearly constant stress, a plateau, results from the narrow length-distribution of tie-molecules. This plateau is not observed during mechanical experiments. This plateau is the direct result of isomolecular tie-molecules. The only way to predict the progressive increase of the stress up to the yields stress observed experimentally is to consider a large length-distribution of tie-molecules. This progressive increase of stress implies a progressive deformation of the crystalline phase. The basic mechanism of plastic deformation is the pull-out of crystalline chain segments by the tie-molecules in extended conformation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A waterborne latex-based technique has been used to prepare acrylic films with laponite contents up to about 25 vol%. The laponite was attached to the surfaces of the latex particles, giving a cellular arrangement of laponite-rich regions at high laponite contents. Two regimes of reinforcement were observed, depending on whether T was above or below T-g, reinforcement at T > T-g being significantly greater than predicted by micromechanical models. Modulated differential scanning calorimetry and dynamic mechanical analysis showed part of the organic content of the films not to contribute to the glass transition. This "rigid amorphous fraction" (RAF) was argued to correspond to intercalated regions of the matrix. However, the RAF alone was insufficient to account for the observed increases in stiffness at T > T-g. The mechanical response is therefore discussed in terms of a four-phase model, in which intercalated laponite stacks are embedded in a matrix with reduced mobility, forming a foam-like structure, in turn embedded in a matrix with the properties of the bulk polymer. (C) 2011 Elsevier Ltd. All rights reserved.

Structural complexity inherited from a microbial synthesis of glycolipids was translated into unique poly(sophorolipid) biomaterials. ROMP polymerization of natural diacetylated lactonic sophorolipids gave a high molecular weight polymer with asymmetric bola-amphiphilic repeating units. The poly(sophorolipid) chain alternates C18 oleic-like aliphatic segments (90% cis-configured double bonds) with bulky diacetylated disaccharide moieties. The solid-state properties were investigated by means of TGA, DSC, TMDSC, and variable-temperature X-ray diffraction. The poly(sophorolipid) is a solid at room temperature that undergoes the glass transition at 61 degrees C and melts at 123 degrees C. The crystal phase is associated with ordered packing of the aliphatic chain segments. The semicrystalline poly(sophorolipid) also displays a long-range order (d = 2.44 nm) involving sophorose groups that is found to persist after crystal phase melting (in high-T diffractograms) with a slightly shortened distance (2.27 nm). Upon annealing at 80 degrees C the poly(sophorolipid) recrystallizes and concomitantly the disaccharide units space out again at 2.44nm. An exothermal phenomenon that immediately follows melting and is revealed by TMDSC might be associated with the observed adjustment of sophorose units spacing in the melt. The peculiar structural organization of this novel biomaterial is discussed.

This thesis presents new insights into the early events of formation of oriented precursors in flow-induced crystallization of polymers, specifically isotactic polypropylene. Experimental approaches are developed to follow the creation of thread-like precursors during flow. The use of model bimodal polymers provides insight on the role of long chains in the mechanism of formation of oriented precursors. The addition of very long chains (3500 kg/mol) at low concentration (< 1% wt) dramatically reduced the stress required to trigger formation of thread-like precursors, which opened a wide range of conditions in which to discover how oriented precursors form. The combination of powerful new methods and model materials exposed a kinetic and mechanistic step prior to propagation of oriented precursors that had not been addressed in prior literature. Furthermore, the present model systems provide a bridge to the flow-induced crystallization phenomena that occur in commercial resins, making it very likely that these well-defined polymers will reveal the underlying physics that governs the effects of flow on morphology and final properties of polymers, and providing a rational basis for molecular design of polyolefins to expand the envelope of accessible properties. The phenomenological effects of flow on polymer crystallization have been known for decades, manifested dramatically in most processing techniques due to the high stresses imposed onto the polymer melt. Processing flows can accelerate the kinetics of crystallization by orders of magnitude, and can induce the formation of highly oriented crystallites that, in turn, impact the final material properties in the solid state. The formation of oriented thread-like precursors is at the heart of these effects of flow on polymer crystallization; however, the fundamental mechanisms underlying their development remain elusive. This lack of understanding frustrates the formulation of a predictive model that relates the polymer molecular characteristics and the imposed processing conditions to the ensuing crystallization kinetics, the final morphology, and hence, the ultimate material properties. Here, we develop experimental approaches that provide insight into the physics of formation of the oriented precursors, which identify the essential elements required in a truly predictive model of flow-induced crystallization. In this work, we build on experimental capabilities of imposing well-defined flow and thermal histories onto a polymer melt, and of utilizing small quantities of material so that model polymers can be investigated, which allows us to isolate the effect of specific molecular characteristics and flow conditions. Our apparatus provides us with real-time measurements that probe a range of shear stresses throughout a slit flow channel; thus, we develop a "depth sectioning method" as a strategy to isolate the contribution to the real-time signal that arises from a specific level of shear stress. This method is of utmost importance since the formation of thread-like precursors depends strongly on stress. To separate the development of oriented precursors during flow from the growth of oriented crystallites on them, we develop an experimental approach, the "temperature-jump," inspired by classical nucleation studies. We use a small concentration of ultra-high molecular weight isotactic polypropylene in a matrix of shorter chains to examine the role of long chains in the creation of thread-like precursors. The use of such high molecular weight chains has revealed a richer behavior than could be observed in earlier studies, indicating that there are two stages in thread formation, kick-off and propagation, and that the stress requirement for the first step is more stringent than for the second. The data are consistent with the hypothesis that the interaction of long chains with the tip of a shish creates a local orientation that is not found elsewhere in the flowing melt. Finally, we combine the two experimental approaches to perform measurements that capture the development of the threads during flow. For intermediate shearing times, our results are well described by the most promising model currently available, the "recoverable strain model," and lay the groundwork for determining the velocity of propagation of threads at different shearing stresses. Also, it suggests that some modifications to the recoverable strain model should be included to correctly capture kick-off and saturation of the formation of threads. The experimental tools described here can be extended to other model materials, for example, to expose the effects of long chain length > 3500 kg/mol and of the stereo-regularity of the long chains. A larger parameter space can be surveyed in the future to provide additional data to test predictive models that connect molecular characteristics of a resin to structure formation under processing conditions.

Process-induced Long-term Deformation Behavior of Injection Molded Semicrystalline Thermoplastics Injection molding is a very complex process because the polymer experiences a complex thermorheological history during molding that influences the molecular orientation, residual stresses, frozen-in free volume and crystallinity inside the part. These generally govern the final part properties. Therefore it is highly desirable to anticipate the effect of process parameters on the resulting microstructure and mechanical properties of the finished part in the long run. In the case of a semicrystalline thermoplastic part, the problem in understanding the deformation behavior arises from its two-phase structure and a tendency exists to concentrate primarily on the effect of the crystalline phase on the deformation behavior, while the contribution of the amorphous phase is less investigated. In this work, the influence of the processing parameters on the deformation behavior of injection molded semicrystalline thermoplastic parts, viz., syndiotactic Polystyrene (sPS) and Polybutylene terepthalate (PBT), has been monitored through creep. The resulting internal structures due to processing have been determined and the deformation behavior has been analyzed. It has been observed that only the rate of cooling shows a remarkable effect on the long-term viscoelastic behavior of an injection molded semicrystalline thermoplastic part as it influences not only the crystalline, but also the free volume fraction, whereas the different states of frozen-in orientations and pressure-induced densification have only a negligible effect. Besides, physical aging also plays an important role in the deformation behavior of the injection moldings which was manifested with the decrease in the tendency to creep. Therefore, it was suggested that the cooling rate during injection molding and the aging time can significantly affect the long-term deformation behavior of the injection molded semicrystalline thermoplastics. The results also showed that when no significant effect is observed in terms of short-term mechanical properties by changing the processing conditions, but while considering the long-term behavior they show a significant effect.

Polyolefins, semicrystalline polymers also known as thermoplastics, are highly desirable because of their material properties, low cost, and ease in processing. The flow and thermal history experienced during processing are known to affect dramatic changes in crystalline kinetics and morphology, dictating the final material properties of solidified products. However, the underlying physics that control crystalline orientation and kinetics is not well understood. To optimize processing conditions and maximize material performance, it is desirable to understand how the interplay of molecular character and flow conditions shape crystalline microstructure. In the last decade, advances in catalyst technology have produced well defined materials enabling the systematic study of molecular influences on flow-induced crystallization. We investigate bimodal blends of polypropylenes (PP) in which we vary the molecular character (concentration, molecular weight, regularity) of the high molecular weight mode. We apply a number of in situ characterization tools (rheo-optics, rheo-WAXD) to the development of transient structure and interpret our findings in light of ex situ examination (polarized light microscopy, TEM) of the final morphology. Blending a well-characterized high molecular weight isotactic polypropylene into a "base iPP" at various concentrations (c), we determined that blends with less than 1% of chains with Mw five times larger than the Mw of the base resin profoundly affected the crystallization kinetics and crystalline morphology of a sheared melt. Beyond unambiguously demonstrating the important role of long chains in the formation of anisotropic crystallization under flow, this approach allowed us to be specific about the length that is meant by "long chains" and the concentration of these chains in the melt. Varying the concentration from below to above c* revealed that the effect of the long chains involves cooperative interactions, evident in the non-linear relationship of the long chain concentration, particularly as c approaches the long chain-long chain overlap concentration. The long chains greatly enhance the formation of threadlike precursors but only mildly enhance the formation of pointlike precursors. In studying a series of blends in which the Mw of the long chain mode was varied, we found that increasing the Mw of the long chain portion of a bimodal blend increased the tendency to form threadlike precursors to oriented crystallization. This was highlighted by a marked decrease in the threshold stress necessary to induce oriented crystalline growth and is related to the separation in time scales between the slowest relaxing chains and the average. Thus, the propagation of shish varies strongly with the separation in time scales between the slowest relaxing chains and the average. Below a threshold ratio of relaxation times (tau_L/tau_S ~ 100) addition of long chains did not change the behavior from that of Base-PP itself. Our analysis of real-time rheo-optical and rheo-WAXD experiments combined with depth dependent information from a novel "depth sectioning" analysis technique uncovers several keys to understanding how anisotropic crystallization is induced by flow. Threads first form near the channel wall, where stress is highest, and grow in length with prolonged flow. After sufficient time, thread length per unit volume saturates, perhaps due to collisions with other threads or crystalline overgrowth from those threads. Prior to saturation, when crystalline overgrowth is negligible, the thread propagation appears to be linear with shearing time. The propagation of threads varies in a nonlinear manner with stress. Finally, we identify a promising set of conditions that can be used to measure the thread propagation velocity for this material if the appropriate length scale can be assigned by microscopy. We examined the effects of long chain regularity on the formation of threadlike precursors, showing that addition of molecular level defects to the high end of the molecular weight distribution effectively raises the threshold stress and mitigates the formation of oriented precursors induced by flow. Our study included a model bimodal blend of isotactic and atactic polypropylene as well as large scale bimodal blends of isotactic polypropylene and a propylene-ethylene copolymer fit for pilot-scale production of nonwoven fabrics. It is noteworthy that the qualitative behavior observed in the melt-spinning process accords well with the trends evident in isothermal shear-induced crystallization. This has value in two respects. Scientifically, it is significant that idealized flow and thermal conditions may well reveal the physics relevant to polymer processing, which involves mixed shear and extension under non-isothermal conditions. Technologically, the ability to screen different resin compositions on a small scale can be used to optimize flow-induced crystallization characteristics prior to scale up.

An investigation was carried out on a three stage method (extrusion/annealing/uniaxial-stretching) (MEAUS) utilized to produce semicrystalline polymeric microporous membranes. The two semicrystalline polymers studied were selected based on a set-of-prerequisites proposed for the formation of highly porous membranes via the method in question. The prerequisites included "fast" crystallization kinetics, presence of an ac relaxation, ability to form a planar stacked lamellar morphology with a "good" crystalline orientation upon melt-extrusion, and rapid heat transfer of the film during extrusion. The first polymer was isotactic poly(4-methyl-1-pentene) (PMP), and the second was polyoxymethylene (POM). Three PMP resins were studied, which differed in weight average molecular weight. Three POM resins were also investigated where two of resins were characterized by relatively narrow molecular weight distributions (MWD) ca 2 while the third POM resin possessed a MWD ca 5.9. The melt-extruded film morphologies and orientation values were a consequence of the melt-relaxation times as a result of the resin characteristics and/or the melt-extrusion conditions. Following the extrusion stage, the effect of annealing (second stage) on film properties was investigated. The annealing variables investigated included the temperature, time, and level of extension applied during annealing. The annealed films were then subjected to the uniaxially stretching stage (third stage) consisting of a cold and hot step, respectively, where deformation was along the extrusion direction. The variables of interest included the cold and hot stretch temperature and extension level. It was found that starting precursor morphology and orientation, annealing conditions, and stretching variables impact the final film microporous morphology and permeability. Additionally, the proposed prerequisites were verified in both the PMP and POM film series. In addition to the MEAUS study, a comprehensive investigation was conducted of the optical properties of blown and cast films made from conventional Ziegler-Natta catalyzed linear low density polyethylene (LLDPE) as well as metallocene-catalyzed LLDPE resins. From this work, it was determined that in PE blown and cast films made using conventional processing conditions, the optical haze properties are adversely affected due to enhanced surface roughness caused by the formation of spherulitic-like superstructures in polymer melts that possess fast relaxing and low melt elasticity rheological characteristics. This optical property study was also published in J. Appl. Polym. Sci., 77(13), 2845, (2000). Ph. D.

Changes in the segmental order and local segmental dynamics of a lamellar microdomain of polystyrene-polydimthylsiloxane (PS-PDMS), induced by low temperature crystallisation of the soft block, were investigated by deuterium NMR spectroscopy.

Solution-processable semiconducting polymers have been explored over the last decades for their potential applications in inexpensively fabricated transistors, diodes and photovoltaic cells. However, a remaining challenge in the field is to control the solid-state self-assembly of polymer chains in thin films devices, as the aspects of (semi)crystallinity, grain boundaries, and chain entanglement can drastically affect intra-and inter-molecular charge transport/transfer and thus device performance. In this short review we examine how the aspects of molecular weight and chain rigidity affect solid-state self-assembly and highlight molecular engineering strategies to tune thin film morphology. Side chain engineering, flexibly linking conjugation segments, and block co-polymer strategies are specifically discussed with respect to their effect on field effect charge carrier mobility in transistors and power conversion efficiency in solar cells. Example systems are taken from recent literature including work from our laboratories to illustrate the potential of molecular engineering semiconducting polymers.

Supramolecular interactions play an important role in defining the structure and the resulting mechanical properties of materials. For instance, interchain hydrogen-bonding in PAs gives them superior strength and stiffness in engineering materials, while the predominance of van der Waals interactions in PE materials is one of the factors responsible for their ductility. In the present thesis, we have strived to achieve novel materials with a useful combination of mechanical properties by incorporating both types of supramolecular interactions into the same material in the form of micro- or nanophase-segregated domains. The first section addresses the challenge of increasing the ductility of a semiaromatic polyamide without compromising strength or stiffness. To this end, we have synthesized amino-telechelic PE and subjected it to high-temperature melt compounding with the polyamide PA6TI. We show that, under these conditions, rapid transamidation reactions between the two materials result in the formation of PA-PE block copolymers, which stabilized the interfaces of the PE particles and resulted in reduced PE domain sizes in the approximate regime where particulate toughening is most efficient (0.1-1 µm). Furthermore, because the PE domains were shown to remain semicrystalline, their presence only induced minimal losses of stiffness and strength. This translated to improved toughness and ductility over blends with non-functional PE at an optimized concentration of 20 wt% modified PE, which was also observed in corresponding glass fiber-reinforced composites. The second section started from the same amino-telechelic PE, aiming to create novel materials comprising hydrogen-bonded supramolecular networks. To this end, we synthesized PE end-modified with ligands capable of forming extended one-dimensional nanostructures by ditopic, multivalent hydrogen bonding, such as oligopeptides or benzene-1,3,5-tricarboxamide (BTA) derivatives. These polymer end groups were designed to form well-defined nanofibrils by co-assembly with low molecular weight oligopeptide or BTA additives. We studied additives and end groups with different core structures and solubilizing substituents and compared the resulting materials to reference systems based on non-modified PE at various additive concentrations, in order to analyze the role of these different molecular parameters on the formation of well-defined one-dimensional nanostructures versus phase separation into crystalline additive precipitates. The presence of the nanofibrils served as reversible physical crosslinks above the PE melting temperature, giving rise to increased melt strength and elasticity, tailorability of rheological properties, and a drastically increased extensibility in the polymer melt, which is relevant for polymer processing procedures that require large degrees of deformation.