Amino-functionalized graphene quantum dots (af-GQDs) with discrete molecular weights and specific edges were self-limitedly extracted from oxidized graphene sheet. Their optical properties can be precisely controlled only by the selective and quantitative functionalization at the edge sites. The af-GQDS exhibit bright colorful fluorescence under a single-wavelength excitation.
SynopsisHigh-resolution 13C-NMR spectra were studied for two different crystalline structures of nylon 6 in the solid state by the crass polarization/magic angle spinning (CP/MAS) method. Two crystalline structures, a-form and y-form, gave different chemical shifts for methylene carbons. The results showed that the hydrogen bonds between intermolecular chains are stronger in the y-form than in the a-form. This strongly supports the results of the X-ray study of nylon 6 by Malta et al. Our results also showed that intramolecular delocalization of positive charges occurs in the y-form through hyperconjugation in which the dihedral angle between the I bond and neighboring a bonds is 3 0 ' while no such effect can be expected in the a-form in which the angle is 0".
A plasma‐polymerized material was produced from hexamethyldisiloxane vapor by a glow discharge polymerization technique. Spectroscopic interpretation of the chemical structure of the polymerized hexamethyldisiloxane was studied by spectroscopic means such as IR, XPS, and NMR. The plasma polymer was barely soluble in the usual organic solvents, although it contained a small amount of the monomer and its oligomers. The IR spectrum indicated that the polymer consisted of SiCH3, SiO, SiCH2, and SiH groups. The surface of the polymer was found to retain structural units similar to the monomer from the XPS measurement. On the other hand, the 13C and 29Si high‐resolution, solid‐state NMR measurements revealed that the plasma polymer was highly crosslinked with a variety of conformations and a number of O atoms surrounding a Si atom. Results from the XPS and NMR spectra suggested that the bulk of the polymer was more oxidized than the surface layer; Si atom was preferentially oxidized. A hypothetical chemical structure was proposed for the polymerized hexamethyl‐disiloxane.
SynopsisThe products in inductively coupled plasma excited in organosilicic compounds were studied on chemical structures by spectroscopic methods. Plasma-polymerized tetrar,dhylsilane (PA) contains not only Si-CH, groups but also Si-H groups on IR and ?%NMR analyses. 13C-NMR spectrum of PA reveals that the crosslinked structure of PA is mainly constructed of CH, and CH groups. Plasma-polymerized octamethylcyclotetrasiloxane (PD, ) is composed of Si-CH, andSi-0 groups. 13C-and ?Si-NMR spectra of PD, point out the highly preservation of the structural units similar to the monomer. These data of PD, suggest that PD, is formed from the ring-opening polymerization by cleavages of Si-0 bonds. 13C-NMR spectrum of poly[methyltrimethoxysilane] (PT) indicates the existence of CH,-0 groups, meanwhile its 29Si-NMR analysis concludes that F'T is chiefly c o m p a d of the structural units similar to the monomer. The surface analyses by XPS of PA, PD,, and F'T suggest that these organosilicic plasma polymers resemble their starting materials.have proven valuable to the study of the chemical structures of the plasma polymers.6-8 We have studied the chemical structures of the plasma-polymerized organosilicic compounds (tetramethylsilane, octamethylcyclotetrasiloxane, and methyltrimethoxysilane) by IR, XPS, and high-resolution solid-state NMR.
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