Cette thèse s'inscrit dans le cadre d'un projet de l'Agence National de Recherche (ANR) dans lequel participent deux sociétés et deux laboratoires universitaires. L'objectif de ce projet consiste à améliorer les propriétés mécaniques (résistance à l'abrasion) et thermiques (température de dégradation) de revêtements fluorés antiadhésifs en y intégrant des nanoparticules de silice. Or, la silice est une charge hydrophile qui se disperse difficilement dans une matrice fluorée. C'est pourquoi nous avons envisagé de modifier sa surface avec des réactifs fluorés, et la nature des divers précurseurs a une influence sur l'amélioration de la dispersion des nanoparticules. Ainsi, nous avons, dans un premier chapitre, étudié la miscibilité et la compatibilité des polymères fluorés entre eux. Les polymères fluorés sont réputés pour leur inertie chimique, hydrophobie et leurs propriétés thermiques très avantageuses. Mais les très bonnes propriétés des polymères fluorés entraînant parfois des difficultés de mise en œuvre, nous avons choisi de travailler avec deux copolymères fluorés, le poly(TFE-co-HFP), un copolymère statistique à base de tétrafluoroéthylène (TFE, -CF2-CF2-) et d'hexafluoropropène (HFP, -CF(CF3)-CF2-) voisin du PTFE utilisé pour les revêtements, et le poly(VDF-co-HFP), un copolymère composé de fluorure de vinylidène (VDF, -CH2-CF2) et d'hexafluoropropène. Ils présentent de bonnes propriétés et sont faciles à employer à l'état fondu de par leurs faibles températures de fusion (respectivement de 140 et 275°C pour le poly(VDF-co-HFP) et le poly(TFE-co-HFP)). Des mélanges binaires à l'état fondu ont été réalisés puis caractérisés entre ces deux copolymères semi-cristallins mais également avec un polyéther fluoré, composé de plusieurs unités d'oxyde d'hexafluoropropène (HFPO, -CF(CF3)CF2O-) totalement amorphe. Les résultats obtenus suite à ces mélanges ont indiqué les trois types de précurseurs fluorés à employer lors des modifications de surface et ce en fonction de la matrice fluorée : composés à base de TFE (-CF2-CF2-), de VDF (-CH2-CF2-) et de l'HFPO (-CF(CF3)CF2O-). Ainsi, le second chapitre est consacré aux stratégies de synthèse de ces précurseurs fluorés contenant des motifs VDF et HFPO. Deux méthodes de polymérisation ont été réalisées : 1) La polymérisation radicalaire par transfert d'iode (ITP) du VDF conduisant à CnF2n+1-[CH2-CF2]m-I ; 2) La polymérisation anionique par ouverture de cycle de l'HFPO permettant la synthèse C3F7O-[CF(CF3)CF2O]-CF(CF3)-COX avec X : groupements fonctionnels. Ces produits ont été caractérisés par spectroscopies RMN du 19F et du 1H, IR, GPC, DRX, ATG et DSC. Les oligomères du TFE (CnF2n+1-I ou CnF2n+1-C2H4-SH avec n= 4 ou 6) n'ont pas été préparés du fait des risques encourus lors de la manipulation du TFE (gaz explosif). Après leurs synthèses, fonctionnalisations et caractérisations, nous les avons greffés à la surface de silices submicroniques. La principale méthode de greffage employé est le « grafting onto » qui permet de modifier la surface des particules inorganiques avec des macromolécules (oligomères ou polymères) et le troisième chapitre présente trois méthodes de greffage : 1) L'addition radicalaire de RFI ou RFC2H4SH sur une double liaison (vinylique ou allylique) ; 2) La condensation d'un oligomère à base d'HFPO fonctionnalisé ester méthylique sur une silice possédant des fonctions amine ; 3) La méthode la plus communément, utilisée l'hydrolyse-condensation, à partir d'oligo(HFPO) fonctionnalisés alkoxysilane. Les méthodes d'analyses employées afin de caractériser ces nanohybrides fluorés sont les spectroscopies RMN 1H et 29Si à l'état solide, IR, les analyses élémentaires et thermogravimétriques. Nous avons utilisé ces différentes stratégie de modifications de surface afin d'obtenir une large gamme de silices modifiées avec des groupements fluorés tout en tenant compte de la miscibilité des chaînes fluorées entre elles (Chapitre 1). / This thesis is part of a project of the National Research Agency (ANR) which involved two companies and two university laboratories. The objective of this project is to improve the mechanical properties (abrasion resistance) and thermal (degradation temperature) nonstick fluorinated coatings by incorporating silica nanoparticles. However, silica is a hydrophilic filler which is hardly dispersed in a fluoridated matrix. Therefore, we planned to modify its surface with fluorinated reagents, and the nature of various precursors has an influence on improving the nanoparticles dispersion. Thus, we, as a first chapter, studied the miscibility and compatibility of the fluoropolymers. Fluoropolymers are known for their very attractive properties like chemical inertness, hydrophobicity and thermal. But these very good properties of fluoropolymers sometimes cause difficulties application, we chose to work with two fluorinated copolymers, poly (TFE-co-HFP), a copolymer based on tetrafluoroethylene (TFE,-CF2-CF2-) and hexafluoropropylene (HFP,-CF(CF3)-CF2-) neighbor of PTFE used for coatings, and poly (VDF-co-HFP), a copolymer composed of vinylidene fluoride (VDF, -CH2-CF2) and hexafluoropropylene. They have good properties and are easy to use in blend due to their low melting temperatures (140 and 275° C for poly (VDF-co-HFP) and poly (TFE-co-HFP), respectively). Blends have been realized and characterized between two semi-crystalline copolymers but also with a fluorinated polyether composed of several units of hexafluoropropylene oxide (HFPO,-CF(CF3)CF2O-) which is completely amorphous. The results obtained from these blends indicated that the three types of precursors can be used for fluorinated surface modifications and in function of the fluoropolymer : compounds are based on TFE (-CF2-CF2-), VDF (-CH2-CF2-) and HFPO (-CF(CF3)CF2O-). Thus, in the second chapter, the synthesis of these fluorinated precursors containing VDF and HFPO units are shown for this, two polymerization methods were carried out : 1) The iodine transfer polymerization (ITP) of VDF ; 2) The anionic polymerization by ring opening of HFPO. These products were characterized by 19F and 1H NMR spectroscopy, FTIR, GPC, XRD, TGA and DSC. Oligomers of the TFE (CnF2n+1-I or CnF2n+1-C2H4-SH with n = 4 or 6) have not been prepared because of the risks incurred during the handling of TFE (explosive gas). After their synthesis, functionalization and characterization, we have grafted them on the surface of silica nanoparticles. The main method used is the "grafting onto" which allows to modify the surface of inorganic particles with macromolecules (oligomers or polymers) and the third chapter presents three methods of grafting : 1) The radical addition of RFI and/or RFC2H4SH on a double bond (vinyl or allyl) ; 2) The condensation of an oligomer based HFPO functionalized methyl ester on a silica with amine functions ; 3) The most commonly used hydrolysis-condensation, using oligo (HFPO) functionalized alkoxysilane. The analysis methods used to characterize these fluorinated nanohybrids are the 1H and 29Si solid state NMR, FTIR, elemental and thermogravimetric analysis. We used these different surface modification to obtain a wide range of modified silica with fluorinated groups. After their characterization, these fluorinated silica are introduced by blend into two fluorinated matrices poly (VDF-co-HFP) and poly (TFE-co-HFP). The fourth is dedicated to the study of nanocomposite poly (VDF-co-HFP) / silica. Initially, a state of the art is presented as this type of composite has been widely discussed in the literature contrary to nanocomposites poly (VDF-co-HFP) or poly (TFE-co-HFP) with fluorinated nanoparticles.

Master thesis deals with the influence of polyvinylacetate, polycaprolactone, poly(butylene-adipate-co-terephtalate) and talc, ethylenevinylacetate, polyethylene glycol and monosodium citrate on the flow properties, mechanical properties and crystallization ability of PLA. The flow properties were studied using the melt flow index and mechanical properties were studied using a tensile test. The crystallinity was studied by differential scanning calorimetry and on a polarization optical microscope equipped with hot stage. Isothermal crystallization was performed at 95 and 105 °C for 3 h and non-isothermal crystallization was performed with a calorimeter at two cooling rates (1 and 10 °C/min). Upon the isothermal crystallization at 95 °C, the formation of denser crystalline structure was observed and the content of crystalline phase increased in most of the samples. The formation of spherulitic structure was observed at 105 °C in samples with 30 % PVAc, 30 % EVA and PEG. Reducing the cooling rate to 1 °C/min at non-isothermal crystallization had nearly no effect on the crystallization process of the most samples; the content of crystalline phase increased in the samples containing PBAT and PEG, which revealed double melting peak during subsequent heating. The crystalline fraction was the most significantly affected by the addition of PEG. All added polymers except PVAc affected the mechanical properties; PBAT, PCL, EVA and PEG increased the strain and decreased the strength and modulus of elasticity. The samples containing monosodium citrate showed unsatisfactory mechanical properties and could not be measured. The samples containing higher concentration of EVA copolymer showed the phase separation.

In the last two decades, hyperbranched (hb) polymers have drawn much attention and obtained intensive research activities both from industry and academia. They are known to have unique and interesting properties which derive from their three dimensional structure and the large number of functional groups. These structural characteristics provide high possibilities for controlling functional group interactions and modifications of other polymers in blends and therefore, they are expected to result in novel materials with desired properties. Furthermore, the easy synthetic accessibility of hb polymers by one-pot synthesis is advantageous as well and allows easy scale-up of laboratory reactions. Having the characteristics as mentioned above, hb polymers are considered good candidates for blend components or melt processing modifiers. In fact, hb polymers have already been used as blend components or additives aiming for different effects. In many cases, reduced viscosity and formation of miscible blends were observed by modification of a linear matrix polymer with hb polymers. More information will be introduced in the following theoretical section. In this work two hb polyester systems based on AB2 and A2+B3 approaches were synthesized and studied. Their possible applications as additives in the blends of linear polyamides were investigated.

L'objectif de notre travail de développer des multi-matériaux de type sandwich acier/polymère/acier destinés au secteur automobile en vue de l'allègement des structures. Ce nouveau matériau doit satisfaire plusieurs critères, à savoir: i) grande déformabilité à froid en vue de l'emboutissage, ii) tenue au fluage à haute température (T=200°C, étape de cataphorèse), iii) tenue en milieu agressif (chaud, humide, brouillard salin). De plus, l'adhésion polymère-métal doit être maîtrisée en vue d'éliminer les phénomènes de délamination lors de l'emboutissage des tôles. Ce sandwich doit être réalisable sur une ligne industrielle dont la température maximale de complexage est limitée à 200°C. Si une solution à chacun de ces points particuliers peut être facilement apportée, la réponse à l'ensemble de ces critères par une formulation unique est beaucoup plus complexe. Nous nous sommes focalisés sur une formulation permettant de répondre au critère de tenue au fluage pour des températures supérieures à 200°C mais dont l'adhésion à chaud sur le métal (étape de complexage sur la ligne industrielle) doit être à inférieure à cette même température de 200°C. Pour cela nous avons développé une formulation à base de polymères immiscibles polyamide 11/polyoléfine fonctionnalisée anhydride maléique compatibilisés in-situ. Nos travaux ont donc porté sur l'optimisation de cette formulation, via le contrôle de la morphologie en vue de l'élaboration d'un film ayant les caractéristiques d'un fluide polymère à contrainte seuil d'écoulement tout en ayant les propriétés d'adhésion adéquate / The aim of this work is to develop multimaterials such as steel/polymer/steel composites for weight savings in automotive industry. To fully take advantage of properties of both steel and polymer materials, adhesion steel-polymer must be well controlled. Moreover, the composite must be compatible with processing on the industrial line and last not least, the structure must be flow resistant during the cataphoresis step (Painting process at 200°C for 30 minutes). This last condition is essential and our work will focuse on the development of compatibilized polymers blend made of polyamide 11 and polyolefin grafted maleic anhydride with yield stress properties. We successfully optimize the formulation via morphological control in order to develop a yield stress fluid with good adhesive properties

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Morphological development during crystallization of thin films of poly(ethylene oxide) (PEO) / poly(methyl methacrylate) (PMMA) blends has been reported. Studies have focused on the effects of the blend composition, PMMA molecular weight, film thickness, and crystallization temperature on the observed crystal morphology. As the blend composition was varied from 90 to 30 wt% PEO, the crystal morphology varied from spherulites to needles and dendrites. Variation of the crystallization temperature and PMMA molecular weight resulted in similar changes in morphology. A morphological map demonstrating the roles of the experimental controls on the observed crystal morphology has been developed. This map was used as a tool for more detailed studies of the observed morphologies and morphological transitions. The dendritic region of the map (~ 30 = 40 wt% PEO) was studied in detail. Changes in the diffusion length were achieved through variation of the PMMA molecular weight, and were shown to influence the secondary sidebranch spacing. Sidebranch spacing measurements revealed that coarsening of the dendritic microstructure occurred well after the competition between diffusion fields of neighboring dendrite arms vanished, indicating the existence of another coarsening mechanism. These studies of dendritic sidebranching indicate that polymer dendrites develop by mechanisms similar to those in small molecules and metals. A number of in-situ observations of morphological transitions have also been reported, including a dense-branched morphology (DBM)/dendrite transition, a DBM/stacked-needle/needle transition, and a transition from dendrites with 90o sidebranching to dendrites with 45o branching or a dense-branched morphology, both of which grow at 45o to the original dendrite trunk. The DBM/dendrite transition occurred over a range of crystallization temperatures, indicating that the transition is not sharp. Crystal growth rate measurements verified this result. The DBM/stacked-needle/needle transitions demonstrated distinct jumps in the crystal growth rate, indicating a change in the growth mechanism or direction. For the transition involving a change in the growth direction, the effective level of noise (fluctuation) was found to be important in morphological selection. The results of this work have helped to define new directions for the study of crystal morphologies, especially in the areas of spherulite formation and dendritic growth. / Ph. D.

This dissertation focuses on the synthesis and characterization of high performance polymers, specifically polybenzimidazoles (PBIs) for gas separation applications and polyimides (PI) for water purification and as interfacial agents for thermoplastic carbon fiber composites. Two methods for improving the gas transport properties (for H2/CO2 separation) of a tetraaminodiphenylsulfone (TADPS)-based polybenzimidazole were investigated. Low molecular weight poly(propylene carbonate) (PPC) and poly(ethylene oxide) (PEO) were incorporated as sacrificial additives that could be removed via a controlled heat treatment protocol. PBI films containing 7 and 11 wt% PPC (blend) and 13 wt% PEO (graft) were fabricated and the gas transport properties and mechanical properties after heat treatment were measured and compared to the PBI homopolymer. After heat treatment, the 7 wt% PPC blend exhibited the highest performance while retaining the toughness exhibited by the PBI homopolymer. Novel sulfonated polyimides and their monomers were synthesized for use as interfacial agents and water purification membranes. Polyimides are high performance polymers that have high thermal, mechanical, and chemical stability. The objective was to assess structure-property relationships of novel sulfonated polyimides prepared by direct polymerization of the diamine monomers. A series of sulfonated polyimides was synthesized using an ester-acid polymerization method with varying degrees of sulfonation (20%, 30%, and 50% disulfonated and 50% and 100% monosulfonated polyimides). The results showed that the toughness of the polyimides in the fully hydrated state was much better than current commercial cation exchange membranes. A 100% disulfonated polyimide (sPI) and poly(amic acid) salt (PAAS) using the same monomers used for the synthesis of Ultem® were utilized as suspending agents for the fabrication of coated sub-micron polyetherimide (PEI) particles. Sub-micron particles were obtained using 1 wt% PAAS and 4 wt% sPI to coat the PEI. The PEI particles were coupled onto ozone treated carbon fibers using a silane coupling agent. SEM images showed a significant amount of particle coating on the treated carbon fibers compared to the non-silane treated carbon fibers. / PHD / This dissertation describes synthetic and processing techniques used to fabricate materials for applications such as, water purification and gas separation. The polymers included in this dissertation include polybenzimidazoles and polyimides, which are materials that have exceptional mechanical and thermal properties. The polybenzimidazoles were specifically used for gas separation, while the polyimides were synthesized for use as water purification membranes and surfactants for coating polyimides and carbon fibers. Gas separation membranes are effective tools for purifying gas mixtures (e.g. H₂/N₂, O₂/N₂, CO₂/CH₄). Additionally, they offer the advantage of being economical and environmentally-friendly compared to other methods of separation (e.g. cryogenic distillation). Many synthetic membranes made from polymers are used commercially, however, very few polymers can be used for elevated temperature separations. Because polybenzimidazoles exhibit high thermal stability, they are excellent candidates for high temperature gas separations (specifically H₂/CO₂ gas mixture). However, polybenzimidazoles have inherently low gas permeabilities. Thus, the focus of this research was to develop a simple method to introduce “pores” into the polymer membrane to improve gas permeability. Water purification is a very important process as the demand for clean water increases with the growing global population. Currently, one-third of the global population experience water scarcity, and by 2025, two-thirds of the world’s population may face water shortages. Multi-stage flash distillation is the most widely used method for water desalination from sea water but it is also the most energy intensive process. Water desalination using polymer membranes (e.g. reverse osmosis, nanofiltration, electrodialysis) has been developed as low energy and environmentally-friendly alternatives for producing clean water. The current state-of-the-art membranes used for water purification lack mechanical integrity and chemical resistance, which complicate and reduce the overall efficiency of the separation process. Thus, the focus of the research was to synthesize polyimide membranes with improved toughness and chemical stability.

No / Small-angle neutron scattering measurements on a series of monodisperse linear entangled polystyrene melts in nonlinear flow through an abrupt 4:1 contraction have been made. Clear signatures of melt deformation and subsequent relaxation can be observed in the scattering patterns, which were taken along the centerline. These data are compared with the predictions of a recently derived molecular theory. Two levels of molecular theory are used: a detailed equation describing the evolution of molecular structure over all length scales relevant to the scattering data and a simplified version of the model, which is suitable for finite element computations. The velocity field for the complex melt flow is computed using the simplified model and scattering predictions are made by feeding these flow histories into the detailed model. The modeling quantitatively captures the full scattering intensity patterns over a broad range of data with independent variation of position within the contraction geometry, bulk flow rate and melt molecular weight. The study provides a strong, quantitative validation of current theoretical ideas concerning the microscopic dynamics of entangled polymers which builds upon existing comparisons with nonlinear mechanical stress data. Furthermore, we are able to confirm the appreciable length scale dependence of relaxation in polymer melts and highlight some wider implications of this phenomenon.