High Performance Polymers

New polysilane-metal complexes structures were obtained by the polycondensation reaction of α,ω-bis(chloromethyl)-polymethylphenylsilane with the Ni (II) complex of bis(salicylidene)ethylenedia-mine (salen). The chloro-functionalized polysilane was obtained by a modified Wurtz coupling procedure at low temperatures. To obtain the polymer-metal complex the resulted macroligand was complexed with metal cations. This structure is characterized by a highly localized electroactivitry in the redox moiety combined with a specific σ conjugative effect in the polysilane chain. Infrared, 1H NMR and UV-vis spectral analysis as well as gel permeation chromatography and thermogravimetric analysis were used to investigate the new chemical structures.

A new polysilane with pendant metal complex segments was synthesized and characterized. For this purpose a macroligand has been prepared starting from a iodopropyl-functionalized polysilane and a bis(salicylideneimine) derivative. Under mild reaction temperature this polymeric ligand was able to form crosslinked structures. The material was then doped with metal cations and was investigated to observe the system behavior near the gelation point. The UV-vis spectrum of the new material indicated that the electronic structures of the conjugate polysilane chain and metal complex remained unaffected by the condensation reaction process. Similar polymeric structures could be useful to build new organic electroconductive devices.

Aromatic side-chain oxadiazole polymer linked with 9,9'-dioctylfluorene was successfully synthesized via Suzuki coupling reaction. Hydroxyphenyl group was attached in the 2-position of the oxadiazole unit in the polymer side chain to control the optical properties of the polymer. We confirmed the presence of the t-butoxycarbonyl group on the hydroxyl group using thermogravimetric analysis, which was incorporated to avoid side reaction during polymerization. We also performed the simple and easy fabrication method for the dual fluorescence image using photochemical cleavage of the t-butoxycarbonyl group from the polymer to induce fluorescence color changes before and after UV irradiation.

A disiloxane dialdehyde was obtained from bis (chloromethyl)disiloxane and p-hydroxybenzal-dehyde and it was used in an equilibration (redistribution) reaction to synthesize an oligomeric dialdehyde. By solution polycondensation, starting from bis(formyl-p-phenoxymethyl)tetramethyldisiloxane and different organic diamines, poly(azomethine)s were obtained. In the case of aromatic diamines with high rigidity, which gave insoluble polymers, different approaches were tested in order to improve the solubility: the use of the dialdehyde having longer siloxane chain, or of a siloxane diamine in a copoly-condensation reaction. The polymers’ structures were confirmed by IR and 1H NMR spectroscopy and by elemental analysis. The structure-properties relationship was studied in terms of solubility, thermal and thermotropic behavior. Most of the obtained poly(azomethine)s has mesomorphic properties, which were studied by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction. The influence of aromatic diamines’ chemical structure on the processability of the siloxane-organic poly(azomethine)s was emphasized.

Physical and gas transport properties of end group-modified 6FDA-TAPOB hyperbranched polyimide (HBPI)-silica hybrid membranes were investigated. Hyperbranched polyamic acids as precursors were synthesized by polycondensation of triamine, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and the molecular end groups were subsequently allowed to react with 3-aminopropyltrimethoxysilane (APTrMOS) and fluorine compound, 3,5-bis(trifluoromethyl)aniline (6FMA) and 1H,1H-heptadecafluorononylamine (17FN). The HBPI-silica hybrids were prepared by sol-gel reaction using the polyamic acids, water, and tetram-ethoxysilane (TMOS). The 5% weight-loss and glass transition temperatures of the hybrids considerably increased with increasing silica content, indicating effective crosslinking at polymer-silica interface mediated by APTrMOS moiety. The CO2, O2, N2, and CH4 permeability coefficients of the hybrids increased with increasing silica content. In particular, 6FMA-modified and 17FN-modified 6FDA-TAPOB HBPI-silica hybrids showed high gas permeability, arising from their high fractional free volumes. The CO2/CH4 selectivity of the hybrids increased remarkably with increasing silica content, whereas their O2/N2 selectivity remained almost constant against silica content. It was concluded that the HBPI-silica hybrids have high thermal stability, high gas permeability, and excellent CO2/CH4 selectivity, and are expected to apply to high-performance gas separation membranes.

The goal of the work presented here was to develop nanocomposites consisting of layered silicates and poly(ethylene terephthalate) (PET). Two nanocomposite preparation methods were compared: first, the usual melt compounding technique, and second, in-situ synthesis of PET in presence of different types of layered silicates. Montmorillonite (MMT) without and with organophilic modification was employed as layered silicate. In most cases, PETs with acceptable properties (molecular weight and discoloration) were synthesized in presence of different MMTs although the molecular weights of the in-situ PETs were lower than the control sample. These materials were used as masterbatch for PET nanocom-posites with 5 wt.% inorganic content. The exfoliation in both types of nanocomposites was not complete, but they showed a good distribution of clay within the polymer matrix.

A new semi-fluorinated perfluorocyclobutyl (PFCB) aryl ether containing polymer was prepared in high yield via the condensation of a commercial 4,4'-((1,2,3,3,4,4-hexafluorocyclobutane-1,2-diyl)bis(oxy))bisphenol (bisphenol T) and bis(trifluorovinyloxyether)biphenyl producing transparent, flexible films. The polymer system was structurally characterized using 1H and 19F NMR and exhibited a high degree of thermal stability as determined by thermogravimetric analysis capacity. The sulfonated analogue showed the highest degree of sulfonation at 27% from ion-exchange chromatography, producing a conductivity of 0.011 S cm-1 at 100% relative humidity.

A series of aromatic polyamides were synthesized by activation of aromatic diamines through a newly improved synthetic method. The polymers described herein were prepared by direct polycon-densation of isophthaloyl chloride (IPC) with silylated aromatic diamines prepared in situ by addition of chloro(trimethyl)silane (CTMS). Moreover, the same polycondensation reaction was carried out in a medium containing pyridine, to investigate the effect of the base as a promoter. The reactions were studied for diamines of different reactivity to demonstrate the feasibility of this synthetic method in polycondensation reactions. An interesting behavior was observed for sterically hindered, and therefore less reactive diamine, 4,4'-methylene-bis(2,6-dimethylaniline). The two activation methods here employed afforded readily polyamides having an inherent viscosity of 2.54 dL g-1 for the most reactive diamine (1a), when CTMS was used as the activating agent, and polyamides having an inherent viscosity of 0.65 dL g-1 for the sterically hindered diamine (1e), using the pair CTMS/Py as the activating agent. The experimental work was supported by calculations of the electronic parameters of the aromatic diamines, using quantum mechanical methods (DFT). Overall, this highly efficient one-pot method provides advantages through an easy handling and simple procedure.

The polysaccharides are important materials in food, pharmaceutical, cosmetic and related biomedical applications. Xanthan gum is a microbial polysaccharide of great commercial significance. It is well known as one of the best thickening polymers due to its high intrinsic stiffness related to the helical conformation stabilized in the presence of excess salt. It is used in a wide variety of foods for a number of important reasons, including emulsion stabilization, temperature stability, compatibility with food ingredients, and its pseudoplastic rheological properties. Due to its properties in thickening aqueous solutions, as a dispersing agent, and stabilizer of emulsions and suspensions, xanthan gum is used in pharmaceutical formulations, cosmetics, and agricultural products, as well as in textile printing pastes, ceramic glazes, slurry explosive formulations, and rust removers. In this work the crosslinking of a mixture of xanthan and lignins in the presence of the epichlorohydrin, leading to superabsorbant hydrogels with high swelling rate in aqueous mediums, was studied. The swelling properties of these composite hydrogels were investigated. Three different types of lignin have been used namely: aspen wood lignin (L), annual fiber crop lignin (GL) and lignin epoxy-modified resin (LER). Semi-interpenetrating polymer network hydrogels in various ratios were prepared. The influence of gravimetric ratio between components of the semi-interpenetrating polymer networks, as well as the kinetics of water sorption will be discussed. The maximum swelling degree of the hydrogels and the swelling rate constant were determined as a function of the hydrogel's composition. It has been established that the nature of lignin significantly influences swelling process, the chemical modified lignin having a particular behavior.

Polyurethanes are known as a class of polymers with very high ‘hemocompatible‘ properties. In this study polyurethanes were prepared in various compositions and in medical purity without using any solvent, catalyst or additives. For the synthesis of polyurethanes, toluene diisocynate, diphenylmethane diisocynate or hexamethylene diisocynate were used as diisocyanate compounds and polypropylene-ethylene glycol or polypropylene glycol were used as polyol compounds. The surfaces were modified with plasma glow-discharge by using various gas atmospheres and by applying different powers. Some samples were also modified by heparin immobilization to increase the blood compatibility. Chemical structure, mechanical strength, thermal behavior, oxygen permeability, water contact angle values, as well as protein and cell attachment capabilities of the prepared and modified polyurethanes were examined as possible candidates for biomedical applications. Plasma altered the chemistry of the surface, increased hydrophilic character, and caused a decrease in protein adsorption as the applied power was increased. On the other hand, an optimum power value which caused maximum attachment for Vero cells was observed. In-vitro experiments carried out with blood cells, plasma modification caused an increase on cell adhesion while further heparin immobilization resulted with a significant decrease.

A novel series of linear, high molecular weight high performance and functional polymers were synthesized by a one-pot, superacid-catalyzed polyhydroxylakylation reaction of carbonyl compounds containing electron-withdrawing substituents, adjacent or relatively close to a carbocation center with non-activated aromatic hydrocarbons. The reactions were performed at room temperature in the Brønsted superacid CF3SO3H (trifluoromethanesulfonic acid, TFSA) and in a mixture of TFSA with methylene chloride, which was used as both solvent and a medium for generation of electrophilic species from the carbonyl component. Polycondensations of 1,1,1-trifluoroacetone, 2,2,2-trifluoroacetohenone, 2,7-dinitrofluorenone, acenaphthenequinone and isatin with aromatic hydrocarbons proceed readily in the presence of superacid at room temperature. The polymers obtained were found to be soluble in the common organic solvents, and flexible transparent films could be cast from the solutions. 1H and 13C NMR analyses of the polymers synthesized revealed their linear, highly regular structure. The polymers also possess high thermostability.

Pentablock poly(L-lactide-co-∊-caprolactone) (PLLA/PCL), with a central fluorinated segment and four PLLA/PCL side chains was synthesized by sequential ring-opening polymerization (ROP) with stannous octoate catalyst in an environmentally benign and clean medium, scCO2. Copolymers of PLLA and PCL are extensively researched for biomedical applications. Fluorinated hydrocarbons are similarly promising for biomedicine, and especially for oxygen-carrying substitute applications. Initially, a fluorinated reactive triblock stabilizer (prepolymer, PCL-FLKT-PCL) with inner fluorinated segment and PCL side chains was synthesized in bulk from a tetraol fluorinated alcohol (FLKT) with a 99% conversion. The prepolymer was then utilized for the synthesis of copolymers in scCO2, where PLLA segments were successively incorporated to the ends of the prepolymer, forming a pentablock structure with four polyester side chains. Reactions were carried out at 75°C and 4000-4500 psi. Solubility studies of the prepolymer and the pentablock copolymer in scCO2 showed effective solubilization at the reaction temperature and pressure. The molecular weights of the products were measured with the aid of gel permeation chromatography; the prepolymer and the copolymer possessed average number molecular weights (Mn) in the range of 13 000 and 24 000 (for 96% conversion of LLA), respectively. Low poly-dispersity indexes were obtained: 1.34 for the prepolymer and 1.08-1.34 for the pentablock copolymer. Material characterization was carried out by 1H NMR, 13C NMR, 19F NMR, differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and scanning electron microscopy (SEM).

Radiation curable polymers are needed for use in space rigidizable inflatable structures (antenna supports, habitats, rovers) for future NASA missions. One approach developed at NASA Glenn utilizes the Diels-Alder trapping of bisdienes (o-xylylenols) generated by the photolysis of o-methylphenyl ketones with bisdienophiles (bismaleimides and bisacrylates). A variety of polyimides and polyesters have been prepared with this chemistry and their properties evaluated. The glass transition temperatures of these resins varied from –27 to over 300°C depending upon monomer structures. Onsets of decomposition, measured by thermogravimetric analysis in air, were in the neighborhood of 300°C and did not vary much with monomer structure. Some monomer systems are liquids at room temperature and have the potential for use in solvent-free UV-cured coatings.

Chain-growth condensation polymerization of 2-bromo-5-chloromagnesio-3-[2-(2-metho-xyethoxy)ethoxy]methylthiophene (2) with Ni catalysts was studied, and the block copolymer of poly2 and poly(3-hexylthiophene) was synthesized by this polymerization method. The polymerization of 2 depended on the ligands of the Ni catalyst, and poly2 with the lowest polydispersity was obtained when 1,2-bis(diphenylphosphino)ethane (dppe) was used as the ligand. The linear relationships between the conversion of 2 and Mn of the polymer and between the feed ratio of 2 to the Ni catalyst and Mn of the polymer indicate that this polymerization proceeds in a chain-growth polymerization manner via a catalyst-transfer condensation polymerization mechanism. The block copolymerization of 2 and 2-bromo-5-chloromagnesio-3-hexylthiophene (1) was then carried out in four ways by changing the order of polymerization of the two monomers and the catalysts. It turned out that the block copolymer was obtained without the formation of the homopolymers by the polymerization of 1 with Ni(dppe)Cl2 or Ni(dppp)Cl2 (dppp = 1,2-bis(diphenylphosphino)propane), followed by the postpolymerization of 2. Of the two catalysts, Ni(dppe)Cl2 resulted in narrower polydispersity of the block copolymer.

Triethoxysilyl functionalized hyperbranched polsiloxysilanes at the focal (FT-HBPSs) and terminal (TT-HBPSs) positions were synthesized to investigate adsorption behavior onto a silicon wafer surface. The surface of the silicon wafer adsorbed with the HBPSs was characterized by X-ray photoelectron spectroscopy, atomic force microscopy (AFM), static and dynamic water contact angle measurements. The AFM images indicated the formation size of dot-like structures were approximately 200 nm. The presence of vinyl terminal groups of FT-HBPSs permitted conversion of the surface from a non-polar hydrocarbon to a polar hydroxylated or carboxylated structures. After the polarity was changed, the surface properties were also studied using the above surface analysis techniques. The dynamic contact angle measurement indicated that the silicon wafer surface modified by FT-HBPSs was more hydrophilic in water than TT-HBPS. This behavior can be explained by the difference of connecting points between HBPS and the silicon wafer surface.

The kinetics associated with the reaction of aromatic and aliphatic diamines with phthalic anhydride in glacial acetic acid was studied. This model system was intended to simulate the synthesis of polyimides from diamines and dianhydrides in molten benzoic acid. The reaction proceeds in two discrete steps, the first acylation occurs by the reaction of the diamine with phthalic anhydride followed by cy-clodehydration of the corresponding bis-(o-carboxyamides). The focus of the work was on the influence of chemical composition and basicity of the diamines on the kinetics. Kinetic and thermodynamic characteristics of model reactions were determined. It was established that acylation of aromatic and aliphatic diamines in acid medium proceeds as a reversible second-order reaction catalyzed by acid medium. On the basis of kinetic data obtained, an explanation is given for the observed phenomenon of reactivity leveling of diamines regardless of the basicity.