Melt‐processable thermosetting polyimide: Synthesis,characterization, fusibility,and property

To obtain a melt‐processable thermosetting polyimide having a high glass‐transition temperature (T_g) and good solvent resistance, the effect of introducing a crosslinkable agent into the polymer chain ends of the melt‐processable polyimide on its physical properties was studied. The polyimide (calculated number‐average molecular weight (M_n) = 11,600 g/mol) capped with the crosslinkable agent exhibited poor melt flowability because its crosslinkable agent reacted at the processing temperature of 360 °C. To reduce the rate of crosslink reaction, two methods were investigated. One was lowering the processing temperature, and the other was decreasing the amount of crosslinkable agent. The low‐molecular‐weight oligomer (calculated M_n = 6300 g/mol) capped with the crosslinkable agent exhibited good melt flowability at the lower processing temperature of 340 °C where the crosslinkable agent did not react. However, the obtained molded part of this oligomer was too brittle to maintain its shape. However, the polyimide (calculated M_n = 11,600 g/mol) partially capped with the crosslinkable agent demonstrated good melt flowability at the processing temperature of 360 °C. Furthermore, the molded part of this resin was strong and tough. In addition, the cured part exhibited high T_g and good solvent resistance. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2395–2404, 2004     

Flow characteristics and spinnability of sols prepared from silicon alkoxide solution

Structural evolution of the solution of tetraethoxysilane hydrolyzed with [H₂O]/[Si(OC₂H₅)₄] = 2 under acidic condition has been investigated by rheological measurements. It was found that the solution behaves as a Newtonian liquid up to a highly viscous state and shows spinnability before gelation when the evaporation of the solvent is allowed during gelation reaction. On the other hand, the solution behaved as a non-Newtonian liquid in the viscous state, showing no spinnability when the evaporation of the solvent was not allowed during the reaction. It was indicated from the Casson plots that the spinnable solution prepared in the open system has no yield stress up to highly viscous states, whereas the non-spinnable solution prepared in the closed system has a yield stress at viscous states. It was proposed that the increase in viscosity of the open system solution is attributable to the concentration of the sol particles whereas that of the closed system solution is attributable to the formation of the three dimensional network in the solution.     

One-pot synthetic method of unsymmetrical diorganyl selenides: reaction of diphenyl diselenide with alkyl halides in the presence of lanthanum metal

A convenient synthetic method of unsymmetrical selenides has been developed. When diphenyl diselenide was allowed to react with two equimolar amounts of primary alkyl iodides and bromides in the presence of an equimolar amount of lanthanum metal, alkyl phenyl selenides were formed in moderate to good yields. For the reaction of primary alkyl chlorides and secondary alkyl iodides, the yields of the selenides were low; however, the yields were dramatically improved by the addition of TMEDA or HMPA. A reaction pathway involving the generation of a lanthanum phenylselenolate intermediate was suggested.     

Phenalenones. IV. Heterocycles from 3-hydroxyphenalenone (I)

3-Hydroxyphenalenone reacts with o-disubstituted benzenes (substituents: NH₂, OH, CH₂OH and SH), aliphatic and aromatic aldehydes to give the various heterocyclic compounds which are fused with phenalene ring. These reactions resemble those of 1,3-cyclohexanediones in many respects.     

Binding of methyl orange and its homologs by powdered nylon 66

Powdered Nylon 66 was prepared as a model of amorphous polymers. The resultant powder polyamide was composed of only amorphous regions. The extent of uptake of the acid azo dyes, a homologous series of methyl orange derivatives, by the polymer was measured in an aqueous solution. The first binding constants and the thermodynamic parameters in the course of the binding were evaluated. The thermodynamic behaviors obtained are very similar to those of crosslinked polyvinylpyrrolidone. The favorable free energy of the binding is accompanied by an entropy gain and an exothermic enthalpy change. The shorter the alkyl chain of the dyes, the more negative is the enthalpy change and, hence, the smaller is the entropy change. The thermodynamic data for butyl orange showed that the binding process is athermal and is wholly an entropic effect. The binding of the dyes to the matrix is entropically favorable as a result of the operation of the hydrophobic effect. In addition, an electrostatic force is operative between the sulfonate group on the dyes and the terminal amino groups on the polyamide.     

Studies on the thermal decomposition of phthalate esters: IX. Thermal decomposition of bis(2-ethylhexyl) phthalate

A flow apparatus equipped with a spray nozzle was developed for investigating the thermal decomposition of esters with high boiling points and viscosities. The thermal decomposition of bis(2-ethylhexyl) phthalate (BEHP), which is a typical plasticizer for poly(vinyl chloride) with a high boiling point and viscosity, was carried out by the use of the flow apparatus. The thermal decomposition products were analysed by gas chromatography and the kinetic parameters were calculated. The kinetic parameter of bis(2-ethylhexyl) phthalate was k_BEHP (s^?1)=4.59·10¹¹ exp(?40600/RT). From a comparison with the values for phthalic esters, it is proposed that a cis-elimination reaction takes place with a two-step mechanism in which the rate-determining step is α-carbon cleavage.     

Structural and dynamic study of chemically modified polyHIPE by solid‐state 13C NMR spectroscopy

The structure of laboratory‐made polyHIPEs was successfully characterized by cross‐polarity/magic‐angle spinning, solid‐state ¹³C NMR experiments. The signals of vinyl groups appeared in the spectrum of the polyHIPE precursor PH? CH?CH₂, which was prepared by the polymerization of the divinylbenzene continuous phase from a highly concentrated reverse emulsion. This material was chemically modified by the regioselective free‐radical addition of thiols to the pendant vinyl groups. Spectra of materials modified by the grafting of C₈ and C₁₂ alkyl chains, PH? SC₈ and PH? SC₁₂, respectively, were produced. The signals of the vinyl groups disappeared in favor of methylene groups. This experiment clearly established that the alkyl chains were covalently bound to the polymer. To elucidate the dynamic aspect of long chains in polyHIPE, we measured the ¹³C spin–lattice relaxation times (T₁) of PH? SC₁₂ from 25 to 100 °C with variable‐temperature, solid‐state, high‐resolution ¹³C NMR spectroscopy, revealing a strong variation in T₁ along the alkyl side chain. Furthermore, the crystallinity of a wide range of chemically modified polyHIPEs, including PH? SC₁₂, was studied with pulse ¹H NMR. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 956–963, 2001     

Complex projective towers and their cohomological rigidity up to dimension six

A complex projective tower, or simply a ?P-tower, is an iterated complex projective fibration starting from a point. In this paper we classify all six-dimensional ?P-towers up to diffeomorphism, and as a consequence we show that all such manifolds are cohomologically rigid, i.e., they are completely determined up to diffeomorphism by their cohomology rings.