High Performance Polymers

β-Cyclodextrin (1 -CD) and 2 -cyclodextrin (2 -CD) (hosts) formed inclusion complexes with 4,4¹-bipyridinium dication derivatives with long chains (guests), in which the substituents on the bipyridinium nitrogen atoms are 1,3-bis(chloromethylphenethyl)-1,1,3,3-tetramethyldisiloxane. The number of 2 -CD molecules threaded onto the polymer chain increases with the length of the guest chain. In contrast, the number of β-CD molecules threaded onto the polymer is approximately 4 corresponding to each molecular chain, due to the repulsive interaction between β-CD and the quaternary bipyridinium units. The complexes were isolated in high yield and characterized by ¹H NMR, ¹³C NMR, X-ray diffraction, thermal and scanning electron micrographs studies. As proven by X-ray analysis, the synthesized polyrotaxanes are crystalline materials with crystalline patterns significantly different from that of native cyclic oligosaccharide. The thermal stabilities of polyrotaxanes are higher than that of the physical mixture between cyclodextrin and the alternating copolymer, denoting the formation of the inclusion complexes. Scanning electron micrographs of polyrotaxanes reveal cubic and linear shapes without a well formed shape. Shape regularity and geometrical regularities in the agglomerating forms can be observed.

Low color, flexible, space-durable polyimide films with inherent and robust electrical conductivity to dissipate electrostatic charge (ESC) have been under investigation as part of a materials development activity for future NASA space missions. The use of single-walled carbon nanotubes (SWCNTs) is one means of achieving this goal. Even though the concentration of SWCNTs needed to achieve ESC dissipation is typically low, it is dependent upon purity, size, dispersion and functionalization. In this study, SWCNTs prepared by the electric arc discharge method were used to synthesize nanocomposites using the LaRC^TM CP2 backbone as the matrix. Pristine and functionalized SWCNTs were mixed with an alkoxysilane terminated amide acid of LaRC ^TM CP2 and the soluble imide form of the polymer and the resultant nanocomposites evaluated for mechanical, thermal and electrical properties. Due to the preparative conditions for the pristine and functionalized SWCNTs, the average aspect ratio for both was comparable. This permitted the assessment of SWCNT functionalization with respect to various interactions (e.g. van der Waals, hydrogen bonding, covalent bond formation, etc.) with the matrix and the macroscopic effects upon nanocomposite properties. The results of the study are described.

A new phosphorus-containing monomer, bis(N-hydroxyethyl-phthalimidyl)-bis(9,10-dihydro-9-oxa-10-oxide-10-phosphaphenanthrene-10-yl)methane, that contains preformed imide rings and flexible linking groups was synthesized. This compound was used to synthesize new phosphorus-containing polyesterimides by solution polycondensation with various aromatic diacide chlorides such as terephthaloyl chloride, terephthaloyl-bis-(4-oxybenzoylchloride), 4-chloroformyl- N(p-chloroformylphenyl)-phthalimide and 2,2-bis(4-chloroformyl- N-phthalimidyl)-diphenylmethane. The rates of the polycondensation reactions were calculated from kinetic investigations. The polymers were readily soluble in polar organic solvents, such as N-methylpyrrolidone, N, N-dimethylacetamide and N,N-dimethylformamide. The polymers were analytically, spectrally and thermally characterized.

As a method of compatibilization of immiscible polyether ether ketone (PEEK)/polysulfone (PSU) blends, the addition of segmented PEEK/PSU block copolymers based on amorphous bisphenol A-containing PEEK was studied. This approach was evaluated for blends consisting of PEEK and PSU homopolymers with different molecular weights and different amounts of compatibilizers (segmented PEEK/PSU block copolymers and reactive end-functionalized PEEK and PSU oligomers). The compatibilizers were added under varying melt-processing conditions and effectively allowed the homopolymers to interact with the segmented block copolymers in the blend. The influence of the compatibilizers on the phase behavior was examined in both binary and ternary blends. Interactions in the amorphous phase, which effectively induce an enhancement of the toughness properties of the final product, could be detected.

In this study, a new synthesis of polybenzoxazoles was studied by reacting 3,3¹-dihydroxy-4,4¹diaminobiphenyl with various p-aromatic dihydroxamoyl chlorides in N,N-dimethylformamide under a nitrogen atmosphere at both room temperature and 150 ³C. The polymers were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, liquid chromatography/mass spectrometry, thermogravimetric analysis and the elemental analysis. Direct current conductivity of HCl acid-doped polybenzimidazole pellets was measured by applying a constant voltage of 5 V. The results of this study are discussed herein.

Poly(phenylquinoxaline)s.(PPQs) are a family of aromatic condensation polymers known for their outstanding thermal and chemical stability. The pendant phenyl groups and chains isomerism improve the solubility and processing characteristics of these polymers. PPQs have also been shown to possess excellent thermo-oxidative stability and thermohydrolytic stability. This stability makes these polymers candidates for development as proton exchange membranes (PEMs) to be used in fuel cells. In addition to thermohydrolytic stability, PEMs require high protonic conductivity and, in order to achieve this they also require high water uptake. Aromatic condensation polymers do not possess these properties, but ionomers derived from them may. The usual method to derivatiziting these polymers is through sulfonation. In the frames of the present investigation we have carried out sulfonation of two PPQs using an H₂SO ₄—oleum mixture (4 : 1) as sulfonating agent at 125 ³C. As a quinoxaline ring is readily formed in acidic medium synthesis of sulfonated PPQs (SPPQs) was also carried out directly from monomers using an H ₂SO₄—oleum mixture as solvent, catalyst and as sulfonating agent. Depending on the conditions of the reaction (temperature, duration, and the ratio of components in a sulfonating mixture) the polymers containing 0.2—6.7% S were prepared. SPPQs are soluble in polar organic solvents1 from the solutions of SPPQs high strength films (3 = 80—100 MPa) were cast. On the basis of sulfonated PPQs new cation-exchange membranes were prepared and investigated. Among the cation-exchange membranes developed those of the greatest interest are proton-exchanging membranes for fuel cells. Proton conductivity of the membranes prepared strongly depends on relative humidity and comparable with the conductivity of Nafion 117.