Nearly one-third of all pharmaceutical substances on the market are able to sorb water into their crystal lattices to form hydrates, which can often compromise stability during processing and/or storage[1]. The tendency of a hydrate to lose its water of crystallization during the manufacturing process of tablet compression is of particular concern to formulation scientists. The amount of water freed as a function of increasing compaction pressure can be explained by the mobility of water within the compact. The mobility of water is determined by the size and shape of the crystal lattice, the numbers and strengths of the hydrogen bonds, and the presence of high-energy sites of disorder[2]. Due to their differing crystal structures, theophylline monohydrate (THM), citric acid monohydrate (CAM), theophylline-water-citric acid cocrystal hydrate (CATHP hydrate), and dicalcium phosphate dihydrate (DCPD) make for interesting model systems to examine the dehydration under mechanical load. The thermal dehydration of both powders and tablets was carried out via thermal gravimetric analysis (TGA). By comparing the temperatures required to start removal of water loss from the powder to that of the tablet, the average amount of water of crystallization that is freed by the compaction process may be quantified. The average amount of water freed by the compaction process results from a competition between the mechanically-induced disorder of the crystal structure that increases the molecular mobility of water within the tablets, and the trapping of water within the interparticulate void spaces at high compaction pressures. The compressibilities, compactabilities, and tabletabilities of the materials were calculated as a function of increasing compaction pressure. The consolidation of the powder bed under pressure was modeled by out-of-die Heckel Analysis which demonstrated the ease of deformation of the model compounds. XRD was utilized to show the decrease in overall order of the crystal lattice as a result of compression as well as anisotropy within the tablets. Crystallographic approaches were utilized to demonstrate the compactness of the crystal structure, and how it affects water mobility. Relaxation pulse experiments (T1, T2) utilizing solid-state NMR were used to directly probe the mobilities of the water molecules within the crystal lattice of THM. The results from T1 and T2 relaxation experiments directly measure the change in molecular mobility of water within the tablets as a function of compaction pressure. This provided independent verification of the trends in molecular mobility and average water freed as a function of compaction pressure observed during TGA dehydration. Raman spectroscopy was used to indirectly measure the polarizability and vibrational motions of THM, and these results corroborate those obtained from ssNMR and TGA dehydration experiments. Overall, this work highlights the potential impact that tablet compression can have on API hydrate stability. 1. Hilfiker R (editor). 2006. Polymorphism in the Pharmaceutical Industry. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co, KGaA. 2. Byrn SR, Pfeiffer RR, Stowell JG. 1999. Solid-state chemistry of drugs. SSCI, Inc.

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As propriedades dielétricas dos materiais têm ganhado importância na aplicação industrial nas últimas décadas, estas propriedades fornecem informações úteis para melhorar o controle de processamento e qualidade dos produtos alimentícios e outros materiais. A espectroscopia dielétrica é amplamente utilizada para estudar a dinâmica molecular em diversos sistemas, nos quais é comum observar o fenômeno de relaxação dielétrica que tem sido associado por vários pesquisadores ao fenômeno de transição vítrea, importante na estabilidade e propriedades dos materiais. O objetivo da tese foi analisar as propriedades dielétricas de produtos alimentícios e filmes biopoliméricos, dando ênfase ao estudo da mobilidade molecular nos filmes; e ao estudo da dinâmica estrutural de alimentos e sua correlação com fatores de qualidade. O estudo foi dividido em várias etapas com objetivos específicos: A primeira consistiu na montagem e startup do equipamento adquirido para medida das propriedades dielétricas (E4980A com 16451B; E5061B com 85070E, Keysight Technologies); A segunda etapa foi dedicada à análise das propriedades dielétricas de goiabada em pasta e suco de laranja na faixa de frequência de 500-3000 MHz, em função do teor de sólidos solúveis e da temperatura visando a geração de correlações que permitiriam fazer um monitoramento durante o processo de produção; Na última etapa foi estudada a mobilidade molecular de filmes de gelatina e nanocompósitos através da análise dielétrica em função da umidade, temperatura, e teor de plastificante ou nanopartícula, na faixa de frequência de 20 Hz - 2 MHz. Análises de calorimetria diferencial de varredura (DSC) e dinâmica mecânica (DMA) foram realizadas para determinar a temperatura de transição vítrea e de relaxação mecânica nos filmes produzidos. A constante dielétrica e o fator de perda dielétrica de suco de laranja e de goiabada em pasta foram dependentes da temperatura e concentração de sólidos solúveis. A temperatura de transição vítrea (Tg) e os tempos de relaxação dielétrica de filmes de gelatina diminuíram com o aumento da concentração de glicerol e com o aumento da umidade relativa de condicionamento. A temperatura de transição vítrea nos filmes nanocompósitos diminuiu com o aumento da umidade relativa de condicionamento. Filmes com 6% de laponita e sem adição de glicerol apresentaram os maiores valores de Tg. Os tempos de relaxação aumentaram ligeiramente com o aumento na concentração de laponita. Foram gerados dados úteis para estimar as propriedades dielétricas de suco de laranja e goiabada em pasta nas principais frequências de uso comercial, 915 e 2450 MHz, através de equações matemáticas em função da temperatura e concentração de sólidos solúveis. O glicerol e especialmente a água afetaram as propriedades dielétricas dos filmes de gelatina refletidas em menores tempos de relaxação, enquanto que as interações da laponita com a gelatina reduziram ligeiramente a mobilidade molecular nos filmes nanocompósitos proporcionando tempos de relaxação maiores. Este tema fez parte do Pilar 4 do projeto CEPID (2013/07914-8) \"Food Research Center\" (FoRC). / The dielectric properties of materials have gained importance in industrial application over the last decades; these properties provide useful information to improve processing and quality control of food products and related materials. The dielectric spectroscopy is widely used to study molecular dynamics in several systems, where it is common to observe the dielectric relaxation phenomenon that has been associated by many researchers to the glass transition phenomenon, important in stability and material properties. The objective of the thesis was to analyze the dielectric properties of food products and biopolymer films, emphasizing the study of molecular mobility in films; and the study of the structural dynamics of food and its correlation with quality factors. The study was divided into several stages with specific goals: The first was the installation and startup of the equipment for measurement of dielectric properties (E4980A with 16451B; E5061B with 85070E, Keysight Technologies); The subsequent step was dedicated to the analysis of the dielectric properties of guava paste and orange juice in frequencies between 500-3000 MHz, as a function of soluble solids content and temperature in order to generate correlations which allow to make a monitoring during the production process; In the last stage, the molecular mobility of gelatin biodegradable films and nanocomposites was studied through dielectric analysis as a function of moisture content, plasticizer or nanoparticle concentration and as a function of temperature, in frequencies between 20 Hz - 2 MHz. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were performed to determine the glass transition and mechanical relaxation temperatures of the films. The dielectric constant and the dielectric loss factor of orange juice and paste guava were dependent on the temperature and soluble solids concentration. The glass transition temperature (Tg) and the dielectric relaxation times of gelatin films decreased with increasing glycerol concentration and with increasing relative humidity of conditioning. The glass transition temperature of the nanocomposite films decreased with the increase of the relative humidity of conditioning. Films with 6% of laponite and without addition of glycerol had the highest values of Tg. Relaxation times increased slightly with increasing laponite concentration. Useful data were generated to estimate the dielectric properties of orange juice and guava paste in the main commercial frequencies, 915 e 2450 MHz, through mathematical equations as a function of temperature and soluble solids content. Glycerol and especially water affected the dielectric properties of gelatin films reflected in lower relaxation times, whereas laponite and gelatin interactions reduced slightly the molecular mobility of the nanocomposite films by providing longer relaxation times. This topic was part of the Pillar 4 of CEPID project (2013 / 07914-8) \"Food Research Center\" (FoRC).

As propriedades dielétricas dos materiais têm ganhado importância na aplicação industrial nas últimas décadas, estas propriedades fornecem informações úteis para melhorar o controle de processamento e qualidade dos produtos alimentícios e outros materiais. A espectroscopia dielétrica é amplamente utilizada para estudar a dinâmica molecular em diversos sistemas, nos quais é comum observar o fenômeno de relaxação dielétrica que tem sido associado por vários pesquisadores ao fenômeno de transição vítrea, importante na estabilidade e propriedades dos materiais. O objetivo da tese foi analisar as propriedades dielétricas de produtos alimentícios e filmes biopoliméricos, dando ênfase ao estudo da mobilidade molecular nos filmes; e ao estudo da dinâmica estrutural de alimentos e sua correlação com fatores de qualidade. O estudo foi dividido em várias etapas com objetivos específicos: A primeira consistiu na montagem e startup do equipamento adquirido para medida das propriedades dielétricas (E4980A com 16451B; E5061B com 85070E, Keysight Technologies); A segunda etapa foi dedicada à análise das propriedades dielétricas de goiabada em pasta e suco de laranja na faixa de frequência de 500-3000 MHz, em função do teor de sólidos solúveis e da temperatura visando a geração de correlações que permitiriam fazer um monitoramento durante o processo de produção; Na última etapa foi estudada a mobilidade molecular de filmes de gelatina e nanocompósitos através da análise dielétrica em função da umidade, temperatura, e teor de plastificante ou nanopartícula, na faixa de frequência de 20 Hz - 2 MHz. Análises de calorimetria diferencial de varredura (DSC) e dinâmica mecânica (DMA) foram realizadas para determinar a temperatura de transição vítrea e de relaxação mecânica nos filmes produzidos. A constante dielétrica e o fator de perda dielétrica de suco de laranja e de goiabada em pasta foram dependentes da temperatura e concentração de sólidos solúveis. A temperatura de transição vítrea (Tg) e os tempos de relaxação dielétrica de filmes de gelatina diminuíram com o aumento da concentração de glicerol e com o aumento da umidade relativa de condicionamento. A temperatura de transição vítrea nos filmes nanocompósitos diminuiu com o aumento da umidade relativa de condicionamento. Filmes com 6% de laponita e sem adição de glicerol apresentaram os maiores valores de Tg. Os tempos de relaxação aumentaram ligeiramente com o aumento na concentração de laponita. Foram gerados dados úteis para estimar as propriedades dielétricas de suco de laranja e goiabada em pasta nas principais frequências de uso comercial, 915 e 2450 MHz, através de equações matemáticas em função da temperatura e concentração de sólidos solúveis. O glicerol e especialmente a água afetaram as propriedades dielétricas dos filmes de gelatina refletidas em menores tempos de relaxação, enquanto que as interações da laponita com a gelatina reduziram ligeiramente a mobilidade molecular nos filmes nanocompósitos proporcionando tempos de relaxação maiores. Este tema fez parte do Pilar 4 do projeto CEPID (2013/07914-8) \"Food Research Center\" (FoRC). / The dielectric properties of materials have gained importance in industrial application over the last decades; these properties provide useful information to improve processing and quality control of food products and related materials. The dielectric spectroscopy is widely used to study molecular dynamics in several systems, where it is common to observe the dielectric relaxation phenomenon that has been associated by many researchers to the glass transition phenomenon, important in stability and material properties. The objective of the thesis was to analyze the dielectric properties of food products and biopolymer films, emphasizing the study of molecular mobility in films; and the study of the structural dynamics of food and its correlation with quality factors. The study was divided into several stages with specific goals: The first was the installation and startup of the equipment for measurement of dielectric properties (E4980A with 16451B; E5061B with 85070E, Keysight Technologies); The subsequent step was dedicated to the analysis of the dielectric properties of guava paste and orange juice in frequencies between 500-3000 MHz, as a function of soluble solids content and temperature in order to generate correlations which allow to make a monitoring during the production process; In the last stage, the molecular mobility of gelatin biodegradable films and nanocomposites was studied through dielectric analysis as a function of moisture content, plasticizer or nanoparticle concentration and as a function of temperature, in frequencies between 20 Hz - 2 MHz. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were performed to determine the glass transition and mechanical relaxation temperatures of the films. The dielectric constant and the dielectric loss factor of orange juice and paste guava were dependent on the temperature and soluble solids concentration. The glass transition temperature (Tg) and the dielectric relaxation times of gelatin films decreased with increasing glycerol concentration and with increasing relative humidity of conditioning. The glass transition temperature of the nanocomposite films decreased with the increase of the relative humidity of conditioning. Films with 6% of laponite and without addition of glycerol had the highest values of Tg. Relaxation times increased slightly with increasing laponite concentration. Useful data were generated to estimate the dielectric properties of orange juice and guava paste in the main commercial frequencies, 915 e 2450 MHz, through mathematical equations as a function of temperature and soluble solids content. Glycerol and especially water affected the dielectric properties of gelatin films reflected in lower relaxation times, whereas laponite and gelatin interactions reduced slightly the molecular mobility of the nanocomposite films by providing longer relaxation times. This topic was part of the Pillar 4 of CEPID project (2013 / 07914-8) \"Food Research Center\" (FoRC).

Ces dernières années, une attention particulière a été portée aux polymères biodégradables et biocompatibles, notamment du point de vue écologique. Le développement de biopolymères pour des applications d'emballage alimentaire implique des exigences industrielles spécifiques telles qu’un bas prix ainsi que de bonnes propriétés mécaniques, thermiques et barrières. Le Polylactide (PLA) a attiré beaucoup d’attention car il est produit à partir de ressources naturelles renouvelables, et en raison de sa capacité de mise en œuvre et de ses bonnes propriétés mécaniques. Pour que le PLA puisse être développé à grande échelle pour des applications industrielles dans le domaine de l’emballage, ses propriétés barrières doivent être améliorées. La cristallisation est une méthode très utilisée pour améliorer les propriétés barrières mais n'est pas suffisante dans le cas du PLA. De nouvelles stratégies sont étudiées pour obtenir des effets plus importants. L'une d'entre elles consiste à confiner géométriquement le polymère jusqu’à l’échelle nano en utilisant le procédé de co-extrusion multicouche combiné éventuellement avec un recuit. Cette technologie respecte l'environnement et a déjà prouvé son efficacité pour améliorer les propriétés barrières aux gaz dans le cas d'autres polymères.Cette étude propose d'abord le développement de films PLA avec des structures cristallines différentes dans le but d'optimiser les conditions de cristallisation pour obtenir de meilleures propriétés barrières à l'oxygène. Parmi les différentes structures cristallines obtenues, la perméabilité est la meilleure lorsque le PLA a été cristallisé rapidement à partir de l’état vitreux pour atteindre un degré de cristallinité élevé et un bon découplage de la phase amorphe et cristalline. Ensuite, le PLLA a été confiné par deux polymères amorphes, le Polystyrène et le Polycarbonate. Nous avons montré que le polymère confineur peut influencer la structure cristalline et la mobilité de la phase amorphe du PLLA, influençant ainsi sa perméabilité. / In recent years, much attention has been focused on biodegradable and biocompatible polymers, particularly from an ecological viewpoint. The development of biopolymers for food-packaging applications implies ecofriendly character to specific industrial requirements as low-cost and good mechanical, thermal and barrier properties. Polylactide (PLA) has been attracting great attention, because it can be obtained from renewable sources, and due to its good process ability and mechanical properties. As one of the major challenges for high performance PLA packaging at a large scale is the improvement of its gas barrier properties, the tailoring of the PLA microstructure. Crystallization is a method used to improve barrier properties but is not sufficient in the case of PLA. New strategies are actually studied to obtained stronger effects. One of them consists in the geometrical confinement of the polymer at the molecular scale using the layer-multiplying co-extrusion process combined eventually with annealing processes to create nanometric thickness layers.This technology is environmentally friendly and has already proved its efficiency to improve the gas barrier properties in case of other polymers. This study first proposes the development of PLA films with different structures crystalline with the aim of optimize the crystallization conditions to get better oxygen barrier properties. Among the different crystalline structures obtained, permeability was better when PLA was rapidly crystallized from glass to reach a high crystallinity degree and decoupling of the amorphous and crystalline phase. Then, PLLA was confined by two amorphous polymers, polystyrene and polycarbonate, and its crystals structure and amorphous mobility was changed. We showed that the confiner polymer could influence PLLA confinement, both in the crystalline phase and in the amorphous phase, thus influencing its permeability.

No / Molecular mobility and physical form of co-spray-dried sugar:lysozyme formulations were evaluated. Co-spray-dried trehalose:lysozyme and sucrose:lysozyme formulations in 1:9, 1:1 and 9:1 ratios (w:w) were stored at 0% RH and 75% RH for 5-6 days. Molecular mobility and physical form of the co-spray-dried formulations after storage were determined by using 13C and 1H solid-state NMR as well as X-ray powder diffractometry. The results showed that increasing sugar content in co-spray-dried formulations stored at 0% RH decreased molecular mobility of the amorphous formulations indicating a close association of the protein and sugar. Exposure of sugar:lysozyme 1:1 and 9:1 formulations to 75% RH led to separation of sugar and protein phases, where the sugar phase was crystalline. The intimate sugar:lysozyme interaction of the formulations stored at 0% RH and the phase separation of the sugar-rich formulations stored at 75% RH were also confirmed by using 13C solid-state NMR spin-lattice relaxation time-filter (T1-filter) measurements. The propensity of sucrose and trehalose to crystallise was similar; however, the results suggest that part of the sugar in the phase-separated formulations remained amorphous and in close association with lysozyme.

Amorphous materials are found in pharmaceutical formulations both as excipients and active ingredients. Indeed, these formulations are becoming an essential strategy for incorporating drugs into well-performing solid dosage forms. However, there is an unmet need of better understanding of the microstructure and component interactions in amorphous formulations to be able to design materials with improved functionalities. The aim of this thesis is to give deepened knowledge about structure-mobility-functionality relationships in amorphous for-mulations by studying composites produced from sugars and filler particles. The structure, the mobility, and physical stability of the composite materials were studied using calorimetry, X-ray diffraction, microscopy, spectroscopy, and molecular dynamics simulations. Further, the moisture sorption of the composites was determined with dynamic vapor sorption. The compression mechanics of the composites was evaluated with compression analysis. It was demonstrated that fillers change the overall properties of the amorphous material. Specifically, the physical stability of the composite was by far improved compared to the amorphous sugar alone. This effect was pronounced for formulations with 60 wt% filler content or more. Amorphous lactose that normally recrystallizes within a few minutes upon humidity exposure, could withstand recrystallization for several months at 60% RH in composites with 80 wt% cellulose nanocrystals (CNC) or sodium montmorillonite (Na-MMT). The increased physical stability of the amorphous sugars was related to intra-particle confinement in extra-particle voids formed by the fillers and to immobilization of the amorphous phase at the surface of the fillers. Also, the composite formation led to increased particle hardness for the lactose/CNC and the lactose/Na-MMT nanocomposites. The largest effect on particle hardness was seen with 40-60 wt% nanofiller and could be related to skeleton formation of the nanofillers within the composite particles. The hygroscopicity for the lactose/Na-MMT nanocomposites decreased as much as 47% compared to ideal simple mixtures of the neat components. The nanofillers did not influence the water sorption capacity in the amorphous domains; however, lactose (intercalated into Na-MMT) interacted with the sodium ions in the interlayer space which led to the lowered hygroscopicity of this phase. The thesis advanced the knowledge of the microstructure of amorphous pharmaceutical com-posites and its relationship with pharmaceutical functionalities. It also presented new approaches for stabilizing the amorphous state by using fillers. The concept illustrated here might be used to understand similar phenomena of stabilization of amorphous formulations.

This work forms part of a project aimed to develop Polyamide 6,6(PA6,6)-based automotive fuel tanks. PA6,6 is a good candidate for technical applications since it possesses good thermo-mechanical properties compared to its weight. These formulations must exhibit good impermeable properties to classic gasoline, to biofuels (gasoline containing ethanol), and to water which is found in the atmosphere, while keeping good impact behavior.The scientific issues are the better understanding of PA6,6-solvent interactions in the case of a series of solvents having different sizes and polarities and also for a set of ternary mixtures composed of ethanol, toluene, and isooctane at various concentrations that model biofuels. The effect of these solvents on the glass transition temperature Tg (molecular mobility signature) was assessed. The effect of additivating or chemically-modifying PA6,6 on the impact and barrier properties of the polymer was studied.In this work, it was described how the nature of a solvent conditions its sorption and its plasticizing effect on PA6,6. It was also observed that the PA6,6 inter-chain interactions also condition the solvent sorption. Moreover, a thermodynamic approach describing the sorption and plasticizing effects of ternary mixtures in PA6,6 was considered and developed. It was also observed that PA6,6 mechanical properties depend or are related to the amorphous phase molecular mobility state.

Les résines composites à base de polymères diméthacrylates sont des biomatériaux fréquemment employés en dentisterie où la matrice est synthétisée in vivo par photopolymérisation en chaîne radicalaire. En Odontologie Conservatrice, la contraction volumique dont cette matrice est le siège au cours de sa synthèse est un inconvénient majeur. Elle est, en effet, à l’origine de contraintes physiques souvent néfastes et mal contrôlées dès lors que le matériau, collé aux murs cavitaires, est élaboré en milieu confiné. Aucune étude n'a permis à ce jour d’analyser de manière approfondie ce phénomène de contraintes de contraction au regard des conditions opératoires de la synthèse de la matrice. Le but de ce travail est donc d'isoler la problématique des contraintes internes en orientant exclusivement l’étude vers l'analyse de la matrice. En élaborant des prototypes à base de Bis-GMA et d’UEDMA et après caractérisation de certaines propriétés physico-chimiques, rhéologiques et thermodynamiques des mélanges de ces comonomères et des copolymères résultants, ce travail a permis de contribuer à une meilleure compréhension de la phénoménologie de la relaxation viscoélastique qui gouverne la dissipation des contraintes de contraction / Composite materials containing polymers are biomaterials frequently employed in dentistry where the matrix is synthesized in vivo by photocured radical chain. In Operative Dentistry, the resulting shrinkage strain produced during the synthesis of this matrix is a major disadvantage. It is, indeed, at the origin of often harmful and badly controlled physical stresses since the material, stuck to the cavity walls, is elaborated in confined surroundings. No study to date allowed analyzing thoroughly this phenomenon of contraction taking into consideration the operating conditions of the synthesis of the matrix. The goal of this work is thus to exclusively isolate the set of problems of the internal stresses by directing the study towards the matrix analysis. By elaborating prototypes based on Bis-GMA and UEDMA and after characterization of certain physicochemical, rheological and thermodynamic properties of mixtures of these comonomers and of the resulting copolymers, this work made it possible to contribute to a better understanding of the phenomenology of the viscoelastic relaxation which governs the dissipation of the shrinkage stress

Ce travail porte sur les mouvements moléculaires dans les caoutchoucs composants les pneumatiques : les polybutadiènes (PB) et les copolymères de polystyrène et polybutadiène (SBR). L’intérêt de cette étude est double : Nous souhaitons à partir de résultat de spectroscopies mécanique et diélectrique, comprendre l’origine moléculaire des relaxations dans ces élastomères, mais aussi voir le rôle de la microstructure chimique dans la mobilité moléculaire. Nous travaillons donc sur des matériaux différents par leur microstructure chimique à travers leurs taux respectifs de butadiène 1,2 vinyle, de butadiène 1,4 cis/trans ou encore de styrène pour les SBR. L’étude de la modification de la microstructure passe aussi par l’ajout de diluants qui servent de perturbateurs à la mobilité. La gamme de température balayée est comprise entre 90K et 350K et permet ainsi l’étude systématique de toutes les relaxations présentent dans les polymères de l’étude : La relaxation β, à plus basse température, la relaxation α pour des températures proches de Tg mais aussi, à plus haute température, les relaxations de bouts de chaine et enfin les phénomènes de reptation de chaines libres pour des températures 90K supérieures à Tg. Les techniques de spectroscopie mécanique (1.10-4/1 Hz) et diélectrique (0,1/1.106Hz) permettent d’obtenir des résultats sur un large domaine fréquence /température. Par ailleurs, les couplages mécanique d'une part et électrique d'autre part étant de nature différente, les informations obtenues par les deux techniques sont complémentaires. Le développement d’un modèle nous permet de démontrer que les mouvements des groupements butadiène 1,2 (vinyle) sont responsables de la contribution haute température de la relaxation β alors que ceux des groupements butadiène 1,4 cis et trans sont responsables de la partie basse température. L’étude approfondie de la relaxation α à l’aide du modèle de Perez amène à penser que ces mêmes groupements butadiène 1,2 vinyles jouent aussi un rôle non négligeable dans cette relaxation α. La dilution par une huile polaire provoque la suppression de la partie haute température de la relaxation β et amène ainsi à une modification de sa mobilité basse température. Diminuer la réticulation dans un polymère entraine revient à augmenter la longueur des bouts de chaine. Ces bouts de chaines peuvent alors relaxer selon les lois de rétraction de bouts de chaine développées par Curro à partir des modèles de Pearson et Helfand. Enfin, les chaines libres introduites dans un polymère réticulé suivent la théorie de la reptation de De Gennes-Doi-Edwards. / This work deals with the study of the molecular mobility in rubbers used for pneumatic applications, namely, polybutadiene (PB) and styrene butadiene rubber (SBR). They exhibit relaxation processes, which are in fact responsible for their main behaviors (adhesion, energy consumption, etc.). From mechanical and dielectric spectroscopy data, we tried to understand the molecular origins of these elastomers relaxation, but, also the role of their chemical microstructure on molecular mobility. We studied materials with different chemicals microstructures, i.e., with different butadiene 1,2 vinyl, butadiene 1,4 cis and 1,4 trans and styrene (for SBR only) ratio. The impact of microstructure modification was also studied with addition of diluents, which modifies the molecular mobility. Experimental temperature range was between 90 and 350K, so all relaxations present in polymer can be studied: the β relaxation at low temperature, the α relaxation for temperature near Tg, the chain-end relaxation at higher temperature and free chain reptation phenomenon at Tg+90K. Mechanical (10-4 Hz to 1 Hz) and dielectric spectroscopy (0,1 Hz to 106 Hz) allow obtaining large frequency range. Besides that, mechanical and dielectric induced stresses are different so both methods are complementary. The β relaxation exhibits two main contributions, so-called here high and low temperature contributions. The use of modeling permits to show that movements responsible for the high temperature contribution are those of butadiene 1,2 vinyl, whereas butadiene 1,4 cis and trans are responsible from low temperature contribution. Perez model used for studying the α relaxation shows that 1,2 vinyl also impact it. High temperature contribution of the β relaxation disappears after dilution by polar oil. Decreasing the crosslinking density in polymers results in the increase of average chain-end length. These chain-ends relax, and it has been found that their relaxation processes follow the chain-end retraction model developed by Curro from Pearson and Helfand works. On the contrary, free chains motions, when introduced in the already cross-linked polymer network follow De Gennes-Doi-Edwards reptation theory.