Stephen T. Wellinghoff

Thermal degradation of urethanes based on 4,4′-diphenylmethane diisocyanate and 1,4-butanediol (MDI/BDO)

Abstract Differential scanning calorimetry (d.s.c.) and gel permeation chromatography (g.p.c.) were used to study the thermal degradation of 4,4′-diphenylmethane/1,4-butanediol based monodisperse urethane model compounds. It was found that the urethane bond was unstable above 170°C in the crystalline state as well as in the molten liquid state. Significant degradation occurred above 200°C. The annealing time was found to be as important as the annealing temperature. The degradation species present were identified by g.p.c. using an absolute molecular weight-retention volume calibration curve. Polymerization as well as depolymerization occurred during the degradation process, so that the molecular weight distribution tended to broaden. The degradation mechanism was found to be thermal dissociation of the urethanes into free isocyanates and alcohols as confirmed by infra-red spectroscopy and gas liquid chromatography. The degradation rate fits well with first order kinetics with respect to the urethane. The triblocks and oligomeric multiblocks of MDI/BDO/poly(propylene oxide) polyol/polyurethanes were also found to be unstable at elevated temperature.

Phase separation studies in RIM polyurethanes catalyst and hard segment crystallinity effects

Polyurethanes were prepared from pure 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BDO) or 1,2-ethane diol (EDO) and α,ω-hydroxyl poly(propylene oxide) (PPO) by reaction injection moulding (RIM). Hard segment (MDI + BDO or EDO) level was 45–50 wt%. The PPO had about 20% ethylene oxide copolymerized in at the chain ends to provide 80% primary OH end groups. Mn was varied from 2000 to 4000. Dibutyl tin dilaurate catalyst and mould temperature were varied. Dynamic mechanical, wide-angle X-ray, differential scanning calorimeter, molecular weight and tensile elongation measurements were made on the RIM polyurethanes. At low reaction rates (low catalyst or temperature) highly crystalline, well phase separated but low molecular weight polymers were produced. At high catalyst or temperature levels more poorly phase separated but high molecular weight, tough polymers resulted. Higher Mn PPO gave better phase separation and EDO gave higher melting temperatures. Preventing hard segment crystallinity by substituting asymmetric MDI or glycols resulted in phase compatibility.

Synthesis of Highly Conducting Heterocyclic F'olycarbazoles by Simultaneous Polymerization and Doping In Liquid Iodine

Abstract Electrically conducting iodine complexes of homopolymers and copolymers of poly(N-akyl-3,3 ‘carbazolyl) are prepared by simultaneous polymerization and doping of N-akyl- and dihalo-derivatives of carbazole in liquid iodine. This represents a direct one-step chemical method of preparing doped conducting polymers from the monomers and dopants analogous to the electrochemical synthetic technique. The amorphous black polymer complexes are stable in air and can be melt cast into films with conductivity in the range 10−-3 to 1 ohm−1cm−1. Preliminary results of Thermal Analysis, FTIR Spectroscopy, and Gel Permeation Chromatography have provided insights into the mechanism and kinetics of polymerization and polymer structures. X-ray Photoelectron Spectroscopy (XPS) data has provided evidence of transfer of charge from the carbazole unit in the polymer complexes.

Synthesis and studies of poly(3,9-carbazolyl), a new conductive polymer displaying high optical transmittance in the visible

Abstract A polycarbazole consisting mostly of 3,9 linkages has been synthesized in a DMF solution by coupling 3,6-diiodocarbazole with an activated copper catalyst. Although this polymer cannot be oxidized by I2, other acceptors such as iodine monochloride or NO+ will convert it to a p-type semiconductor with a conductivity as high as 1 ohm−1 cm−1. A unique property of the oxidized polymer complex is that it displays a maximum transmittance in the visible at 600 nm and a broad near-i.r. band at 2300 nm. In a rigorously oxygen- and water-free environment, coupling between radical cations on adjacent chains produced by NO+ oxidation takes place at the remaining iodine-substituted 6,6′ positions. The 2300 nm band disappears in favor of a band at 900 nm in the crosslinked material. The decomposition pathway for bromine or ICl-oxidized material, however, involves halogenation of the ring. The large shift of the long-wavelength absorbance of the radical cation on the 3,9-linked polymer versus that found on the carbazole monomer suggests that a significant number of adjacent carbazole units are close to planarity. This must provide a significant pathway for electronic transport.

Electrically conducting complexes of poly(3,6-N-methylcarbazolyl methylene

Abstract Poly(3,6- N -methylcarbazoly methylene) prepared by acid-catalysed condensation polymerization of N -methylcarbazole with formaldehyde exhibits p-type semiconducting properties when doped with electron acceptors such as iodine, bromine, nitrosyl tetrafluoroborate and nitrosyl hexafluoroantimonate. The polymer samples have T g in the range 100 – 148 °C, chain length in the range 13 – 25, and a molecular weight distribution of 1.17 –1.51. The polymer complexes with dopant anion (I 3 − , Br 3 − , BF 4 − ) to polymer repeating unit ratio of 0.67 – 0.95 have a d.c. conductivity of 10 −3 to 10 −1 ohm −1 cm −1 and a positive thermoelectric voltage at 23 °C. An important new feature of the methylene-bridged polycarbazole conducting polymers is doping-induced polymer backbone conjugation of the form CH 2 →=CH. Evidence for this oxidation mechanism, converting methylene linkage to methine linkages, includes elemental analysis, infrared spectra, proton NMR and electron spin resonance results.

A transmission electron microscopy study of hexagonal ice

The morphologies of fast-frozen, thin-film samples of pure and dilute solutions of salts and surfactants in hexagonal ice are investigated with transmission electron microscopy. The cold-stage microscopy technique is described briefly and limitations imposed by the equipment and the sample itself are discussed. Ice grains, grain boundaries, dislocations, and stacking faults are imaged before radiolysis from the electron beam can alter their structures. The technique shows that screw dislocations in the ice basal plane are common, in accord with observations from X-ray topography and etch-replication microscopy. It also makes visible nonbasal dislocations in hexagonal ice, including dislocations in first prismatic planes, nonprismatic dislocation loops, and stacking faults on first pyramidal planes; heretofore, these defects have not been confirmed experimentally. Implications of the work for cold-stage microscopy of microstructured fluids are mentioned.

The Role of Polymer Cations in The Polymerization and Electrical Conductivity of Polycarbazole

Abstract The high electrical conductivities (lohm−1cm−1) in 3,3’ polycarbazole charge transfer complexes originate from hopping of radical cations delocalized over only two carbazole units. Although some intramolecular transport must occur a significant intermolecular hopping component must be present. In fact there is significant evidence from model compound studies that distinct bound states exist between radical cations on adjacent chains. The radical cations in the N-methyl substituted polymers are so stable that the conductivity remains unchanged for months in air. These same radical cations can propagate a polymerization reaction through exposed chain ends in molten iodine or bromine solvents. Polymerizations, charge transfer doping, solvent casting thus can be carried out by simply dissolving monomer in the molten halogen. The polymerizing liquid iodine solutions can be reduced by S2O4,= to produce neutral polymer.

Protective group synthesis of poly-N-hydro-(3,6-carbazolyl)☆

Abstract Poly-N-trityl-(3,6-carbazolyl), PNTPMCZ, has been synthesized in pyridine solution using an activated nickel catalyst. 9-Trityl-3,6-diiodocarbazole was polymerized and the triphenylmethyl group subsequently removed by acid hydrolysis. The N-protected monomer was made by a phase-transfer reaction employing 3,6-diiodocarbazole, a benzotriethylammonium chloride catalyst, basic solution and triphenylmethyl chloride. A wide variety of N-substituents can be obtained in this way, allowing the molecular design of polycarbazolyls to be controlled. In addition, weakly-bound N-substituents can be employed for solubility enhancement during reaction and subsequently partially or fully cleaved from the polymer by acid hydrolysis. Poly-N-hydro-(3,6-carbazolyl), PNHCZ, obtained from PNTPMCZ, forms iodine complexes with conductivities of 10−1 ohm−1 cm−1 at room temperature. The visible-near-i.r. spectra suggest that the same radical cations responsible for conductivity in poly-N-methyl-(3,6-carbazolyl) are present. Direct comparisons of the structure and physical properties of PTPMCICZ (a predominantly poly-N-hydro-(3,6-carbazolyl) synthesized in liquid iodine) are made.

Inherent ductility in amorphous Ta2O5 films

Thin films (30 to 80 nm) of refractory tantalum metal were successfully sputter-deposited on uniformly deformable fluoropolymer and polyimide substrates in stress free form. These films were later anodized into amorphous Ta2O5 which is a non-porous (barriertype) oxide with excellent corrosion resistant properties. X-ray photo-emission spectroscopy studies were carried out on tantalum and Ta2O5 to determine the chemical composition and oxidation states of elements. Thin tantalum and Ta2O5 films on fluoropolymer substrates contained fluorine as an impurity while similar films on polyimide substrate contained no fluorine and, in general, fewer impurities. Both thin tantalum films and the corresponding anodic oxides, when deformed in tension to 10% strain, exhibited the expected ductile behaviour of metals where slip bands were observed in the electron microscope. In some cases, minor cracks were observed in the deformed anodic films due to suspected local detachment of the film from the substrate.