Synthesis and characterization of main-chain bile acid-based degradable polymers

Les acides biliaires sont des composés naturels existants dans le corps humain. Leur biocompatibilité, leur caractère amphiphile et la rigidité de leur noyau stéroïdien, ainsi que l’excellent contrôle de leurs modifications chimiques, en font de remarquables candidats pour la préparation de matériaux biodégradables pour le relargage de médicaments et l'ingénierie tissulaire. Nous avons préparé une variété de polymères à base d’acides biliaires ayant de hautes masses molaires. Des monomères macrocycliques ont été synthétisés à partir de diènes composés de chaînes alkyles flexibles attachées à un noyau d'acide biliaire via des liens esters ou amides. Ces synthèses ont été réalisées par la fermeture de cycle par métathèse, utilisant le catalyseur de Grubbs de première génération. Les macrocycles obtenus ont ensuite été polymérisés par ouverture de cycle, entropiquement induite le catalyseur de Grubbs de seconde génération. Des copolymères ont également été préparés à partir de monolactones d'acide ricinoléique et de monomères cycliques de triester d’acide cholique via la même méthode. Les propriétés thermiques et mécaniques et la dégradabilité de ces polymères ont été étudiées. Elles peuvent être modulées en modifiant les différents groupes fonctionnels décorant l’acide biliaire et en ayant recours à la copolymérisation. La variation des caractéristiques physiques de ces polymères biocompatibles permet de moduler d’autres propriétés utiles, tel que l’effet de mémoire de forme qui est important pour des applications biomédicales.

Synthesis of polyelectrolyte brushes on silica-based substrates through surface-initiated polymerization : brush characterization and responsiveness to variation in pH and ionic strength

Les brosses de polyélectrolytes font l’objet d’une attention particulière pour de nombreuses applications car elles présentent la capacité de changer de conformation et, par conséquent, de propriétés de surface en réponse aux conditions environnementales appliquées. Le contrôle des principaux paramètres de ces brosses telles que l'épaisseur, la composition et l'architecture macromoléculaire, est essentiel pour obtenir des polymères greffés bien définis. Ceci est possible avec la Polymérisation Radicalaire par Transfert d’Atomes - Initiée à partir de la Surface (PRTA-IS), qui permet la synthèse de brosses polymériques de manière contrôlée à partir d’une couche d'amorceurs immobilisés de manière covalente sur une surface. Le premier exemple d’une synthèse directe de brosses de poly(acide acrylique) (PAA) par polymérisation radicalaire dans l’eau a été démontré. Par greffage d’un marqueur fluorescent aux brosses de PAA et via l’utilisation de la microscopie de fluorescence par réflexion totale interne, le dégreffage du PAA en temps réel a pu être investigué. Des conditions environnementales de pH ≥ 9,5 en présence de sel, se sont avérées critiques pour la stabilité de la liaison substrat-amorceur, conduisant au dégreffage du polymère. Afin de protéger de l’hydrolyse cette liaison substrat-amorceur sensible et prévenir le dégreffage non souhaité du polymère, un espaceur hydrophobique de polystyrène (PS) a été inséré entre l'amorceur et le bloc de PAA stimuli-répondant. Les brosses de PS-PAA obtenues étaient stables pour des conditions extrêmes de pH et de force ionique. La réponse de ces brosses de copolymère bloc a été étudiée in situ par ellipsométrie, et le changement réversible de conformation collapsée à étirée, induit par les variations de pH a été démontré. De plus, des différences de conformation provenant des interactions du bloc de PAA avec des ions métalliques de valence variable ont été obtenues. Le copolymère bloc étudié semble donc prometteur pour la conception de matériaux répondant rapidement a divers stimuli. Par la suite, il a été démontré qu’un acide phosphonique pouvait être employé en tant qu’ amorceur PRTA-IS comme alternative aux organosilanes. Cet amorceur phosphonate a été greffé pour la première fois avec succès sur des substrats de silice et une PRTA-IS en milieux aqueux a permis la synthèse de brosses de PAA et de poly(sulfopropyl méthacrylate). La résistance accrue à l’hydrolyse de la liaison Sisubstrat-O- Pamorceur a été confirmée pour une large gamme de pH 7,5 à 10,5 et a permis l’étude des propriétés de friction des brosses de PAA sous différentes conditions expérimentales par mesure de forces de surface. Malgré la stabilité des brosses de PAA à haute charge appliquée, les études des propriétés de friction ne révèlent pas de changement significatif du coefficient de friction en fonction du pH et de la force ionique.

Supramolecular polymers azo-containing : photo-responsive block copolymer elastomers and homopolymers

Beaucoup d'efforts dans le domaine des matériaux polymères sont déployés pour développer de nouveaux matériaux fonctionnels pour des applications spécifiques, souvent très sophistiquées, en employant des méthodes simplifiées de synthèse et de préparation. Cette thèse porte sur les polymères photosensibles – i.e. des matériaux fonctionnels qui répondent de diverses manières à la lumière – qui sont préparés à l'aide de la chimie supramoléculaire – i.e. une méthode de préparation qui repose sur l'auto-assemblage spontané de motifs moléculaires plus simples via des interactions non covalentes pour former le matériau final désiré. Deux types de matériaux photosensibles ont été ciblés, à savoir les élastomères thermoplastiques à base de copolymères à blocs (TPE) et les complexes d'homopolymères photosensibles. Les TPEs sont des matériaux bien connus, et même commercialisés, qui sont généralement composés d’un copolymère tribloc, avec un bloc central très flexible et des blocs terminaux rigides qui présentent une séparation de phase menant à des domaines durs isolés, composés des blocs terminaux rigides, dans une matrice molle formée du bloc central flexible, et ils ont l'avantage d'être recyclable. Pour la première fois, au meilleur de notre connaissance, nous avons préparé ces matériaux avec des propriétés photosensibles, basé sur la complexation supramoléculaire entre un copolymère tribloc simple parent et une petite molécule possédant une fonctionnalité photosensible via un groupe azobenzène. Plus précisément, il s’agit de la complexation ionique entre la forme quaternisée d'un copolymère à blocs, le poly(méthacrylate de diméthylaminoéthyle)-poly(acrylate de n-butyle)-poly(méthacrylate de diméthylaminoéthyle) (PDM-PnBA-PDM), synthétisé par polymérisation radicalaire par transfert d’atomes (ATRP), et l'orange de méthyle (MO), un composé azo disponible commercialement comportant un groupement SO3 -. Le PnBA possède une température de transition vitreuse en dessous de la température ambiante (-46 °C) et les blocs terminaux de PDM complexés avec le MO ont une température de transition vitreuse élevée (140-180 °C, en fonction de la masse molaire). Des tests simples d'élasticité montrent que les copolymères à blocs complexés avec des fractions massiques allant de 20 à 30% présentent un caractère élastomère. Des mesures d’AFM et de TEM (microscopie à force atomique et électronique à ii transmission) de films préparés à l’aide de la méthode de la tournette, montrent une corrélation entre le caractère élastomère et les morphologies où les blocs rigides forment une phase minoritaire dispersée (domaines sphériques ou cylindriques courts). Une phase dure continue (morphologie inversée) est observée pour une fraction massique en blocs rigides d'environ 37%, ce qui est beaucoup plus faible que celle observée pour les copolymères à blocs neutres, dû aux interactions ioniques. La réversibilité de la photoisomérisation a été démontrée pour ces matériaux, à la fois en solution et sous forme de film. La synthèse du copolymère à blocs PDM-PnBA-PDM a ensuite été optimisée en utilisant la technique d'échange d'halogène en ATRP, ainsi qu’en apportant d'autres modifications à la recette de polymérisation. Des produits monodisperses ont été obtenus à la fois pour la macroamorceur et le copolymère à blocs. À partir d'un seul copolymère à blocs parent, une série de copolymères à blocs partiellement/complètement quaternisés et complexés ont été préparés. Des tests préliminaires de traction sur les copolymères à blocs complexés avec le MO ont montré que leur élasticité est corrélée avec la fraction massique du bloc dur, qui peut être ajustée par le degré de quaternisation et de complexation. Finalement, une série de complexes d'homopolymères auto-assemblés à partir du PDM et de trois dérivés azobenzènes portant des groupes (OH, COOH et SO3) capables d'interactions directionnelles avec le groupement amino du PDM ont été préparés, où les dérivés azo sont associés avec le PDM, respectivement, via des interactions hydrogène, des liaisons ioniques combinées à une liaison hydrogène à travers un transfert de proton (acidebase), et des interactions purement ioniques. L'influence de la teneur en azo et du type de liaison sur la facilité d’inscription des réseaux de diffraction (SRG) a été étudiée. L’efficacité de diffraction des SRGs et la profondeur des réseaux inscrits à partir de films préparés à la méthode de la tournette montrent que la liaison ionique et une teneur élevée en azo conduit à une formation plus efficace des SRGs.

Lactide polymerization with iron alkoxide complexes

Les essais préliminaires pour préparer des alcoolates de fer à partir du bichlorure ou bibromure de fer (II), en les combinant avec des ligands de type diimino pyridine, ont engendré la formation de complexes homoleptiques et hétéroleptiques, dépendant des substituants sur les branches imines du ligand. Ces complexes homoleptiques octaédriques et paramagnétiques ont été étudiés par rapport à leurs propriétés spectroscopiques et cristallographiques. De plus, la synthèse des complexes de fer hétéroleptique a engendré de bons précurseurs penta-coordonnés pour les réactions de substitution de ligands avec des alcoolates de métaux alcalins, de manière à produire les dialcoolates de fer (II) désirés. Des techniques d’analyse telles que la spectroscopie UV-vis, l’analyse élémentaire, la spectrométrie de masse à haute résolution et la cristallographie aux rayons X ont été utilisées pour caractériser ces complexes de fer. L’activité catalytique de ces complexes de fer (II) a aussi été étudiée par rapport à la polymérisation du lactide; les dialcoolates convoités ont été générés in-situ en raison de la difficulté à produire et à isoler les dérivés alcoolates des complexes diimino pyridine de fer. Une étude approfondie a aussi été faite sur les réactions de polymérisation, surtout par rapport aux valeurs de conversion à l’échelle du temps, ainsi qu’à la tacticité des chaines de polymères obtenues. Ces analyses ont été effectuées par l’entremise de la spectroscopie de résonance magnétique nucléaire, de la chromatographie d’exclusion stérique, et de la spectrométrie de masse MALDI (désorption-ionisation laser assistée par matrice).

Polymer Nanocomposites: Crystallization, Reinforcement and Conductivity through SWNTs

The current research investigates the possibility of using single walled carbon nanotubes (SWNTs) as filler in polymers to impart several properties to the matrix polymer. SWNTs in a polymer matrix like poly(ethylene terephthalate) induce nucleation in its melt crystallization, provide effective reinforcement and impart electrical conductivity. We adopt a simple melt compounding technique for incorporating the nanotubes into the polymer matrix. For attaining a better dispersion of the filler, an ultrasound assisted dissolution-evaporation method has also been tried. The resulting enhancement in the materials properties indicates an improved disentanglement of the nanotube ropes, which in turn provides effective matrix-filler interaction. PET-SWNT nanocomposite fibers prepared through melt spinning followed by subsequent drawing are also found to have significantly higher mechanical propertiesas compared to pristine PET fiber.SWNTs also find applications in composites based on elastomers such as natural rubber as they can impart electrical conductivity with simultaneous improvement in the mechanical properties.

Photothermal and photoacoustic investigations on certain polymers and semi conducting materials

Material synthesizing and characterization has been one of the major areas of scientific research for the past few decades. Various techniques have been suggested for the preparation and characterization of thin films and bulk samples according to the industrial and scientific applications. Material characterization implies the determination of the electrical, magnetic, optical or thermal properties of the material under study. Though it is possible to study all these properties of a material, we concentrate on the thermal and optical properties of certain polymers. The thermal properties are detennined using photothermal beam deflection technique and the optical properties are obtained from various spectroscopic analyses. In addition, thermal properties of a class of semiconducting compounds, copper delafossites, arc determined by photoacoustic technique.Photothermal technique is one of the most powerful tools for non-destructive characterization of materials. This forms a broad class of technique, which includes laser calorimetry, pyroelectric technique, photoacollstics, photothermal radiometric technique, photothermal beam deflection technique etc. However, the choice of a suitable technique depends upon the nature of sample and its environment, purpose of measurement, nature of light source used etc. The polynler samples under the present investigation are thermally thin and optically transparent at the excitation (pump beam) wavelength. Photothermal beam deflection technique is advantageous in that it can be used for the detennination of thermal diffusivity of samples irrespective of them being thermally thick or thennally thin and optically opaque or optically transparent. Hence of all the abovementioned techniques, photothemlal beam deflection technique is employed for the successful determination of thermal diffusivity of these polymer samples. However, the semi conducting samples studied are themlally thick and optically opaque and therefore, a much simpler photoacoustic technique is used for the thermal characterization.The production of polymer thin film samples has gained considerable attention for the past few years. Different techniques like plasma polymerization, electron bombardment, ultra violet irradiation and thermal evaporation can be used for the preparation of polymer thin films from their respective monomers. Among these, plasma polymerization or glow discharge polymerization has been widely lIsed for polymer thin fi Im preparation. At the earlier stages of the discovery, the plasma polymerization technique was not treated as a standard method for preparation of polymers. This method gained importance only when they were used to make special coatings on metals and began to be recognized as a technique for synthesizing polymers. Thc well-recognized concept of conventional polymerization is based on molecular processcs by which thc size of the molecule increases and rearrangemcnt of atoms within a molecule seldom occurs. However, polymer formation in plasma is recognized as an atomic process in contrast to the above molecular process. These films are pinhole free, highly branched and cross linked, heat resistant, exceptionally dielectric etc. The optical properties like the direct and indirect bandgaps, refractive indices etc of certain plasma polymerized thin films prepared are determined from the UV -VIS-NIR absorption and transmission spectra. The possible linkage in the formation of the polymers is suggested by comparing the FTIR spectra of the monomer and the polymer. The thermal diffusivity has been measured using the photothermal beam deflection technique as stated earlier. This technique measures the refractive index gradient established in the sample surface and in the adjacent coupling medium, by passing another optical beam (probe beam) through this region and hence the name probe beam deflection. The deflection is detected using a position sensitive detector and its output is fed to a lock-in-amplifIer from which the amplitude and phase of the deflection can be directly obtained. The amplitude and phase of the deflection signal is suitably analyzed for determining the thermal diffusivity.Another class of compounds under the present investigation is copper delafossites. These samples in the form of pellets are thermally thick and optically opaque. Thermal diffusivity of such semiconductors is investigated using the photoacoustic technique, which measures the pressure change using an elcctret microphone. The output of the microphone is fed to a lock-in-amplificr to obtain the amplitude and phase from which the thermal properties are obtained. The variation in thermal diffusivity with composition is studied.

Studies on Some Aspects of Light Beam Propagation Through Certain Nonlinear Media

This thesis deals with the study of light beam propagation through different nonlinear media. Analytical and numerical methods are used to show the formation of solitonS in these media. Basic experiments have also been performed to show the formation of a self-written waveguide in a photopolymer. The variational method is used for the analytical analysis throughout the thesis. Numerical method based on the finite-difference forms of the original partial differential equation is used for the numerical analysis.In Chapter 2, we have studied two kinds of solitons, the (2 + 1) D spatial solitons and the (3 + l)D spatio-temporal solitons in a cubic-quintic medium in the presence of multiphoton ionization.In Chapter 3, we have studied the evolution of light beam through a different kind of nonlinear media, the photorcfractive polymer. We study modulational instability and beam propagation through a photorefractive polymer in the presence of absorption losses. The one dimensional beam propagation through the nonlinear medium is studied using variational and numerical methods. Stable soliton propagation is observed both analytically and numerically.Chapter 4 deals with the study of modulational instability in a photorefractive crystal in the presence of wave mixing effects. Modulational instability in a photorefractive medium is studied in the presence of two wave mixing. We then propose and derive a model for forward four wave mixing in the photorefractive medium and investigate the modulational instability induced by four wave mixing effects. By using the standard linear stability analysis the instability gain is obtained.Chapter 5 deals with the study of self-written waveguides. Besides the usual analytical analysis, basic experiments were done showing the formation of self-written waveguide in a photopolymer system. The formation of a directional coupler in a photopolymer system is studied theoretically in Chapter 6. We propose and study, using the variational approximation as well as numerical simulation, the evolution of a probe beam through a directional coupler formed in a photopolymer system.

Linear nucleation of polymers

The use of high-melting fibres as linear nuclei for quiescent polymeric melts is instrumental in providing the superior mechanical properties of polymeric self-composites. It also has inherent advantages in the elucidation of fundamental aspects of polymeric crystallization and self-organization, not least in allowing systematic microscopic studies of polymeric crystallization from nucleation through to the growth interface. This has demonstrated explicitly that lamellae develop in two distinct ways, for slower and faster growth, depending on whether fold packing has or has not time to order before the next molecular layer is added with only the former leading to banded growth in linear polyethylene. Other gains in understanding concern cellulation and morphological instability, internuclear interference, isothermal lamellar thickening and banded growth being a consequence of the partial relief of initial surface stress. (c) 2006 Elsevier Ltd. All rights reserved.

Syntheses and crystal structures of two new coordination polymers of Cd(II) using organic spacer and inorganic-bridging ligands

Two new cadmium (II) complexes [Cd(hmt)(dca)(2)] (n) (1) and [Cd-3(hmt)(2)(SeCN)(6)(H2O)(2)] (n) (2) (hmt=hexamethylenetetramine, dca=dicyanamide) have been synthesized and characterized by X-ray single-crystal analysis. The complex 1 is a 2D rectangular grid of octahedral cadmium (II) with CdN6 chromophore where cadmium centers are doubly bridged by dicyanamide and hmt along a-axis, which are interlinked by dicyanamide running along c-axis. Whereas, complex 2 is a 1D chain of octahedral cadmium (II) with a three-leg ladder topology running along a-axis. The Cd(II) centers are doubly bridged through SeCN (infinite rail) along a-axis and singly bridged by hmt (two-step rung) along c-axis, having cadmium centers with CdSe2N3O and CdSe2N4 chromophores. The adjacent chains through H-bonding between coordinated water and hmt, and (SeSe)-Se-... interaction are extended to 2D supramolecular architecture.

Synthesis, structural analysis, and magnetic behaviour of three fumarate bridged coordination polymers: five-fold interpenetrated diamond-like net of Ni-II, sheets of Ni-II and Co-II

The hydrothermal reactions of Ni(NO3)(2).6H(2)O, disodium fumarate (fum) and 1,2-bis(4-pyridyl)ethane (bpe)/1,3-bis(4-pyridyl) propane (bpp) in aqueous-methanol medium yield one 3-D and one 2-D metal-organic hybrid material, [Ni(fum)(bpe)] (1) and [Ni(fum)(bpp)(H2O)] (2), respectively. Complex 1 possesses a novel unprecedented structure, the first example of an "unusual mode" of a five-fold distorted interpenetrated network with metal-ligand linkages where the four six-membered windows in each adamantane-type cage are different. The structural characterization of complex 2 evidences a buckled sheet where nickel ions are in a distorted octahedral geometry, with two carboxylic groups, one acting as a bis-chelate, the other as a bis-monodentate ligand. The metal ion completes the coordination sphere through one water molecule and two bpp nitrogens in cis position. Variable-temperature magnetic measurements of complexes 1 and 2 reveal the existence of very weak antiferromagnetic intramolecular interactions and/or the presence of single-ion zero field splitting (D) of isolated Ni-II ions in both the compounds. Experimentally, both the J parameters are close, comparable and very small. Considering zero-field splitting of Ni-II, the calculated D values are in agreement with values reported in the literature for Ni-II ions. Complex 3, [{Co(phen)}(2)(fum)(2)] (phen=1,10-phenanthroline) is obtained by diffusing methanolic solution of 1,10-phenanthroline on an aqueous layer of disodium fumarate and Co(NO3)(2).6H(2)O. It consists of dimeric Co-II(phen) units, doubly bridged by carboxylate groups in a distorted syn-syn fashion. These fumarate anions act as bis-chelates to form corrugated sheets. The 2D layer has a (4,4) topology, with the nodes represented by the centres of the dimers. The magnetic data were fitted ignoring the very weak coupling through the fumarate pathway and using a dimer model.

Two new mu-(1,3-azido)-bridged polymers: alternating single and double bridges in a 1D nickel(II) complex and uniform bridge in a 2D copper(II) complex: Syntheses, single-crystal structures and magnetic studies

Two polymeric azido bridged complexes [Ni2L2(N-3)(3)](n)(ClO4). (1) and [Cu(bpdS)(2)(N-3)],(ClO4),(H2O)(2.5n) (2) [L = Schiff base, obtained from the condensation of pyridine-2-aldehyde with N,N,2,2-tetramethyl-1,3-propanediamine; bpds = 4,4'-bipyridyl disulfide] have been synthesized and their crystal structures have been determined. Complex 1, C26H42ClN15Ni2O4, crystallizes in a triclinic system, space group P1 with a 8.089(13), b = 9.392(14), c = 12.267(18) angstrom, a = 107.28(l), b 95.95(1), gamma = 96.92(1)degrees and Z = 2; complex 2, C20H21ClCuN7O6.5S4, crystallizes in an orthorhombic system, space group Pnna with a = 10.839(14), b = 13.208(17), c = 19.75(2) angstrom and Z = 4. The crystal structure of I consists of 1D polymers of nickel(L) units, alternatively connected by single and double bridging mu-(1,3-N-3) ligand with isolated perchlorate anions. Variable temperature magnetic susceptibility data of the complex have been measured and the fitting,of magnetic data was carried out applying the Borris-Almenar formula for such types of alternating one-dimensional S = 1 systems, based on the Hamiltonian H = -J Sigma(S2iS2i-1 + aS(2i)S(2i+1)). The best-fit parameters obtained are J = -106.7 +/- 2 cm(-1); a = 0.82 +/- 0.02; g = 2.21 +/- 0.02. Complex 2 is a 2D network of 4,4 topology with the nodes occupied by the Cu-II ions, and the edges formed by single azide and double bpds connectors. The perchlorate anions are located between pairs of bpds. The magnetic data have been fitted considering the complex as a pseudo-one-dimensional system, with all copper((II)) atoms linked by [mu(1,3-azido) bridging ligands at axial positions (long Cu...N-3 distances) since the coupling through long bpds is almost nil. The best-fit parameters obtained with this model are J = -1.21 +/- 0.2 cm(-1), g 2.14 +/- 0.02. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).

Self-assembled healable materials through a combination of pi-pi stacking and hydrogen bonding

The discovery of polymers with stimuli responsive physical properties is a rapidly expanding area of research. At the forefront of the field are self-healing polymers, which, when fractured can regain the mechanical properties of the material either autonomically, or in response to a stimulus. It has long been known that it is possible to promote healing in conventional thermoplastics by heating the fracture zone above the Tg of the polymer under pressure. This process requires reptation and subsequent re-entanglement of macromolecules across the fracture void, which serves to bridge, and ‘heal’ the crack. The timescale for this mechanism is highly dependent on the molecular weight of the polymer being studied. This process is in contrast to that required to affect healing in supramolecular polymers such as the plasticised, hydrogen bonded elastomer reported by Leibler et al. The disparity in bond energies between the non-covalent and covalent bonds within supramolecular polymers results in fractures propagating through scission of the comparatively weak supramolecular interactions, rather than through breaking the stronger, covalent bonds. Thus, during the healing process the macromolecules surrounding the fracture site only need sufficient energy to re-engage their supramolecular interactions in order to regenerate the strength of the pristine material. Herein we describe the design, synthesis and optimization of a new class of supramolecular polymer blends that harness the reversible nature of pi-pi stacking and hydrogen bonding interactions to produce self-supporting films with facile healable characteristics.

Coupling between mesogenic units and polymer backbone in side-chain liquid crystal polymers and elastomers

The levels of alignment of the mesogenic units and of the polymer backbone trajectory for polyacrylate based nematic side-chain liquid crystal polymers and elastomers were evaluated by using wide angle X-ray and small angle neutron scattering procedures. The X-ray scattering measurements show that substantial levels of preferred orientation of the mesogenic units may be introduced through magnetic fields for uncrosslinked polymers and through mechanical extension for liquid crystal elastomers. Small angle neutron scattering measurements show that for highly aligned samples an anisotropic polymer backbone trajectory is observed in which the envelope is slightly extended by ∼ 10% in the direction parallel to the axis of alignment of the mesogenic units. The sense of this coupling differs from that recorded for other uncrosslinked side-chain liquid crystal polymers. Possible mechanisms to account for this anisotropy and its relationship to the properties of liquid crystal elastomers are discussed. The observed deformation behaviour of the liquid crystal elastomer is non-affine and this appears to confirm the dominating influence of the liquid crystal order of the side chains on the mechanical properties of these novel networks.

Modelling the structure of a polymer glass poly(methylmethacrylate) through neutron scattering experiments

Determination of the local structure of a polymer glass by scattering methods is complex due to the number of spatial and orientational correlations, both from within the polymer chain (intrachain) and between neighbouring chains (interchain), from which the scattering arises. Recently considerable advances have been made in the structural analysis of relatively simple polymers such as poly(ethylene) through the use of broad Q neutron scattering data tightly coupled to atomistic modelling procedures. This paper presents the results of an investigation into the use of these procedures for the analysis of the local structure of a-PMMA which is chemically more complex with a much greater number of intrachain structural parameters. We have utilised high quality neutron scattering data obtained using SANDALS at ISIS coupled with computer models representing both the single chain and bulk polymer system. Several different modelling approaches have been explored which encompass such techniques as Reverse Monte Carlo refinement and energy minimisation and their relative merits and successes are discussed. These different approaches highlight structural parameters which any realistic model of glassy atactic PMMA must replicate.

Cinnamate ester containing liquid crystalline side chain polymers

The synthesis of methacrylate esters of 4-cyanophenyl-(4-(ω-hydroxyalkyloxy)) cinnamates, with spacer lengths of 2 and 6 methylene units and the synthesis of the corresponding acrylate ester with a spacer of 2 methylene units are described. The methacrylate monomers were polymerized by free radical polymerization, both as homopolymers and as copolymers with the analogous benzoate monomer of spacer length 6. The acrylate ester could not be polymerized successfully under the same reaction conditions. Polymers were characterized by NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermo-optic observations. Of the monomers prepared, only the cinnamate with a hexamethylene spacer shows a mesophase, seen on supercooling of the melt. All of the polymers prepared were liquid crystalline, with smectic behavior predominating in the polymethacrylates with the longer spacer group. A narrow nematic region is seen just below the clearing temperature with a range of 3–9°C, nematic character is increased in the copolymer series with the degree of incorporation of the cinnamate monomer with the spacer group of length 2.