Evidence of distinct water species in cellulosic environments from broad-line NMR

Broad-line NMR measurements were made on water in cellulosic samples. The spectra for oriented rayon at 65% relative humidity and room temperature consisted of a visually apparent doublet (S_D) and a narrow singlet (S_N) which was shifted upfield about 7 ppm from the center of the doublet. The doublet separation varied as A(3 cos²θ—1), where θ is the angle between the fiber axis and the magnetic field; the maximum doublet separation was 350 mG at both 15.1 and 56.4 MHz, indicating the doublet is dipolar in origin. The peak-to-peak linewidth of the narrow singlet was orientation and field dependent. The upfield shift of the narrow singlet from the doublet center was field dependent. Spectra for vacuum-treated rayon consisted of only the narrow singlet, which was orientation dependent. The doublet separation decreases with increasing moisture content and is essentially zero for oriented rayon samples at 100% relative humidity; the resulting spectra due to the collapsed doublet and S_N singlet was an asymmetric line. Temperature-dependent measurements were made on oriented rayon at 65% relative humidity with the fiber axis parallel to the magnetic field; when the temperature was increased from about 0° the peak-to-peak linewidth of the doublet halves and the doublet separation decreased. As the temperature was increased from about 30 to about 65°C, a previously unobserved singlet (S_E) became visible. The relative amplitudes of the three lines varied with temperature as follows: The S_E singlet increased, the S_D doublet decreased, and the amplitude of the S_N singlet remained constant. Measurements using oriented cotton samples and randomly packed rayon samples indicated that the NMR line shape of the water spectra depends upon the physical properties of the macromolecular substrate. The doublet component of the spectra is attributed to a water species (S_D) which is highly bonded to the macromolecular substrate. The S_E singlet is attributed to an energetic water species (S_E) which is rapidly tumbling in the macromolecular environment. The S_N singlet is not due to free water.     

Effect of ionizing radiation on the dynamic mechanical properties of an epoxy and a graphite fiber/epoxy composite

TGDDM/DDS epoxy and T300/NARMCO 5208 composite specimens were exposed to 0.5 MeV electrons to dose levels up to 10,000 Mrad, and the effects of radiation on the mechanical properties were characterized using dynamic mechanical analysis (DMA). In nominally cured specimens there remain unreacted epoxide groups because the epoxy system vitrifies during the cure, preventing additional reaction. DMA shows that ionizing radiation continues the reactions of epoxide groups. Also, the ultimate glass transition is shown to decrease monotonically with radiation dose. The room temperature elastic modulus of the epoxy increases slightly with radiation, but at temperatures exceeding 100°C there is a slight decrease with radiation. There is a dynamic loss phenomena associated with the composites, not seen in the epoxy, that is thought to be due to the interphase region between the fiber and the matrix.     

Electrophilic superdelocalizability and carcinogenesis by polycyclic aromatic hydrocarbons—Pullman theory

A correlation is shown between carcinogenic potency and K-region electrophilic superdelocalizability for a variety of aromatic compounds.     

Factors affecting H2O absorption of the epoxy tetraglycidyl-4,4′-diaminodiphenyl methane cured with diaminodiphenyl sulfone

It was found that the amount of water absorbed at room temperature in cured tetraglycidyl-4,4′-diaminodiphenyl methane/diaminodiphenyl sulfone epoxy resins increases as the curing time or temperature increases while the amount of tetrahydrofuran-soluble extractables and the room temperature density decreases. These data suggest that the free volume increases with the extent of cure and the resins become more accessible to water. While the driving force for water absorption is the electrostatic attraction between water and the functional groups in the epoxy, the results suggest that equilibrium H₂O absorption is determined primarily by unoccupied volume of the epoxy resin.     

Effects of ionizing radiation on epoxy,graphite fiber and epoxy/graphite fiber composites. Part I: Surface energy changes

Surface energy changes of an epoxy based on tetraglycidyl diaminodiphenyl methane (TGDDM)/diaminodiphenyl sulfone (DDS), T-300 graphite fiber, and T-300/5208 (graphite fiber/epoxy) composites have been investigated after irradiation with 0.5 MeV electrons. The surface energy of TGDDM-DDS epoxy increases monotonically with radiation doses up to 1,000 Mrad mainly due to increased concentration of polar groups. IR and ESCA spectral evidence indicates that carbonyl groups are formed, probably from the tertiary hydrogen at the carbon where the ? OH group is attached in the cured epoxy. The polarity of the graphite fiber and the graphite fiber/epoxy interface also increases with radiation dose. These results and the roles of oxygen are discussed in connection with mechanical properties of epoxy/graphite fiber composites exposed to ionizing radiation.     

Lipase-catalyzed Irreversible Transesterification of Secondary Alcohols Using Isopropenyl Acetate

Summary. Asymmetric acetylation of a set of secondary alcohols with the innocuous acyl donor isopropenyl acetate catalyzed by a lipase from Pseudomonas cepacia immobilized on ceramic particles (PSL-C) in toluene as organic medium afforded the chiral alcohols and the corresponding acetates in high enantiomeric excess (up to 99%). An effective baseline separation of the enantiomers of both substrate and product was performed in one analysis without derivatization using gas chromatography on a new chiral stationary phase (CSP) Chirasil--Dex containing an undecamethylene spacer (C11-Chirasil-Dex).Received November 27, 2002; accepted (revised) January 9, 2003 Published online June 2, 2003