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Titolo:
Solid-state C-13 NMR and H-1 CRAMPS investigations of the hydration process and hydrogen bonding for poly(vinyl alcohol) films
Autore:
Masuda, K; Kaji, H; Horii, F;
Indirizzi:
Kyoto Univ, Chem Res Inst, Kyoto 6110011, Japan Kyoto Univ Kyoto Japan 6110011 Univ, Chem Res Inst, Kyoto 6110011, Japan
Titolo Testata:
POLYMER JOURNAL
fascicolo: 4, volume: 33, anno: 2001,
pagine: 356 - 363
SICI:
0032-3896(2001)33:4<356:SCNAHC>2.0.ZU;2-D
Fonte:
ISI
Lingua:
ENG
Soggetto:
CHAIN CONFORMATION; POLYVINYL-ALCOHOL); FIBERS; WATER;
Keywords:
poly(vinyl alcohol); crystal structure; hydration; hydrogen bonding; conformation; CP/MAS C-13 NMR; H-1 CRAMPS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
35
Recensione:
Indirizzi per estratti:
Indirizzo: Horii, F Kyoto Univ, Chem Res Inst, Kyoto 6110011, Japan Kyoto Univ Kyoto Japan 6110011 m Res Inst, Kyoto 6110011, Japan
Citazione:
K. Masuda et al., "Solid-state C-13 NMR and H-1 CRAMPS investigations of the hydration process and hydrogen bonding for poly(vinyl alcohol) films", POLYM J, 33(4), 2001, pp. 356-363

Abstract

The hydration process and resulting hydrogen bonding for atactic poly(vinyl alcohol) (A-PVA) films have been investigated by high-resolution solid-state NMR spectroscopy. In H-1 CRAMPS spectra for the A-PVA films which are dried after soaked in deuterated water for different periods, the prominent decrease in intensity is observed within 5 min for the resonance line assigned to the intermolecular hydrogen-bonded OH (OHinter) groups while such anintensity reduction occurs over about 30 min for the line ascribed to the intramolecular hydrogen bonded-OH (OBintra) groups. This fact indicates that the exchange between the OH protons and deuteriums of deuterated water ismore preferably induced for the OHinter groups compared to the case of theOHintra groups in the noncrystalline region. In contrast, all OH protons in the crystalline region, including OH protons free from hydrogen bonding that are selectively allowed to exist in this region, are found to undergo the exchange with deuteriums at a much slower rate. It is also found by the C-13 spin-lattice relaxation analysis that there exist three components with different T-IC values assigned to the crystalline, less mobile, and mobile components in the A-PVA films with the water content of 0.82 g-water/g-PVA. The line shape analysis of the CH resonance line for the crystalline component reveals that the probability of the formation of intramolecular hydrogen bond in the meso sequence significantly increases by the addition of water. In the less mobile component the intra- and intermolecular hydrogen bonds are still kept irrespective of the enhanced molecular motion induced by the hydration but the gauche conformation markedly increases in mole fraction probably as a result of partial breaking of hydrogen bonding. In contrast, the mobile component is subjected to rapid exchanges among different conformations and hydrogen bonds, resulting in the appearance of the sharp triplet assignable to the CH carbons in the mm, mr, and rr sequences like the spectrum in solution. Finally the size of the crystallites is estimated to be about 26 nm by the analysis of the H-1 spin diffusion process from thewater-swollen noncrystalline region to the crystalline region.

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Documento generato il 05/12/20 alle ore 19:58:27