DETERMINATION OF DEGREE OF SUBSTITUTION (DS) AND MOLAR SUBSTITUTION (MS) OF CELLULOSE ETHERS BY SOLID-STATE 13C NMR SPECTROSCOPY
Abstract
The work is devoted to determining the substitution parameters of some commercial cellulose ethers by solid-state 13C NMR spectroscopy. The substitution parameters are the degree of substitution (DS) and molar substitution (MS). The objects of study are commercial additives based on hydroxyethyl cellulose (HEC), hydroxypropyl methyl cellulose (HPMC) and hydroxyethyl methyl cellulose (HEMC). In this paper, the degree of substitution (DS) and molar substitution (MS) were determined, and the distribution of the substituents at positions C-2, C-3 and C-6 of the glucopyranose link was established. The calculation of the degree of substitution (DS) and molar substitution (MS) is based on an analysis of relative intensity values of the spectral regions in the solid-state NMR spectra of cellulose ethers and microcrystalline cellulose. Thus the degree of substitution and molar substitution was determined: MSHEC = 1,41 иDSHEC = 1,08; MSHPMC = 0,69 и DSHPMC = 1,78; MSHEMC = 0,74иDSHEMC = 2,19. Comparison of the results with the literature data shows the effectiveness of the method. The proposed method differs from other existing methods in that it is a simple and informative.
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