No abstract

New hybrid organic−inorganic materials which incorporate the bisimide functionality were synthesized by sol−gel condensation of bisimide monomers containing pendant triethoxysilyl groups. Monomers were prepared by transimidation of bis (2-aminopyridyl)imides with (3-aminopropyl)triethoxysilane. This synthesis was applicable to a variety of commercially available bisanhydrides and did not result in the evolution of water which causes premature hydrolysis and condensation of the trialkoxysilyl group. Solid-state NMR (29Si, 13C, and 15N) was utilized to characterize the polysilsesquioxane bis-imides. Nitrogen sorption porosimetry was used to determine the surface area. The thermal and mechanical characteristics of the resultant materials were measured and compared to linear polyimides.

In this study, we utilized the substitution geometry of triethoxysilyl groups about an organic bridging group to control the outcome of the sol-gel polymerization process. The substitution geometry of two triethoxysilyl groups about a carbon-carbon double bond was determined to have a profound effect on sol-gel polymerizations of the E (1) and Z (2) ethenylene-bridged monomers and vinylidene-bridged monomer (3) and on the porosity in the resulting xerogels. 29 Si NMR and chemical ionization mass spectrometry were used to elucidate the early sol-gel chemistry in the acid-catalyzed polymerizations of 1-3. Trans substitution about the ethenylene-bridging group in 1 led to acyclic and monocyclic dimers and trimers as condensation products under acidic conditions and only microporous gels under both acidic and basic conditions. In contrast, cyclization reactions dominated the sol-gel chemistry of 2 beginning with intramolecular cyclization to give the cyclic disilsesquioxane (4) and continued with the formation of cyclic oligomers, including a bicyclic dimer. The cyclization of 2 slowed the rate of gelation compared to 1 and afforded microporous xerogels under acidic conditions and mesoporous gels under basic conditions. The sol-gel chemistry of the vinylidene monomer (3) was strongly retarded by the formation of a cyclic dimer (5). Only mesoporous gels were formed under basic conditions after 9 months; no gels were obtained under acidic conditions.

We report γ-ray dosimeters using carbon nanotubes wrapped with metastable poly(olefin sulfone)s (POSs) that readily depolymerize when exposed to ionizing radiation. New POSs, designed for wrapping single-walled carbon nanotubes (SWCNTs), are synthesized and characterized. The resulting POS-SWCNT composites serve as the active transducer in a novel class of γ-ray dosimeters. In our devices, polymer degradation results in immediate changes in the electronic potential of the POS-SWCNT active layers by decreasing the electron tunneling barriers between individualized tubes and by creating enhanced cofacial π-π electron contacts. By incorporating the SWCNT-POS composites into small resistive device platforms, we establish a rare example of real-time detection and dosimetry of radioactive ionizing radiation using organic-based materials. We show that the sensitivity of our platform closely depends on the intrinsic stability of the polymer matrix, the opacity toward γ-rays, and the dispersion efficiency (i.e., the individualization and isolation of the individual SWCNT charge carriers). Resistance decreases up to 65% after irradiation with a 40 krad dose demonstrates the high sensitivity of this novel class of γ-ray sensors. In addition, the detection mechanism was evaluated using a commercial capacitive device platform. The ease of fabrication and low power consumption of these small and inexpensive sensor platforms combined with appealing sensitivity parameters establishes the potential of the poly(olefin sulfone)-SWCNT composites to serve as a new transduction material in γ-ray sensor applications.

Remote and automated detection of organic compounds in subsurface aquifers is crucial to superfund monitoring and environmental remediation. Current monitoring techniques use expensive laboratory instruments and trained personnel. The use of a filled tubular preconcentrator combined with a chemicapacitive detector array presents an attractive option for the unattended monitoring of these compounds. Five preconcentrator materials were exposed to common target compounds of subsurface remediation projects (1,1,2-trichloroethane, trichloroethylene, t-1,2-dichloroethylene, benzene, and perchloroethylene). Rapid heating of the tube caused the collected, concentrated effluent to pass over the surface of a chemicapacitive detector array coated with four different sorbent polymers. A system containing a porous ladder polymer and the sensor array was subsequently used to sample the analytes injected onto sand in a laboratory test, simulating a subsurface environment. With extended collection times, effective detection limits of 5 ± 3 ppbV for 1,1,2-trichloroethane and 145 ± 60 ppbV for benzene were achieved. Effects of the preconcentrator material structure, the collection time, and sensor material on the system performance were observed. The resultant system presents a solution for remote, periodic monitoring of chlorinated organic compounds and other volatile organic compounds in a soil matrix.