Characterization of ethylcellulose with different degrees of substitution (DS): A diffuse-reflectance infrared study

The structural features of ethylcellulose polymers were studied by FTIR spectroscopy in the diffuse reflectance mode. Attempts to develop a correlation between structural parameters, such as the degree of substitution (DS, the average number of hydroxyls substituted by the etherifying agent) and the OH stretching band profile, were made. Infrared spectroscopy of ethylcellulose polymers showed a sharp band at 2900 cm(-1), associated with a CH stretching vibration, and a broader band at higher wavenumber, which corresponds to OH stretching modes. The OH band is in turn comprised of two components centred at 3500 (band I) and 3300 cm(-1) (band II). The intensity of band I was insensitive to the DS and was attributed to the stretching vibration of hydroxyl groups bonded to C1 and C4 positions of terminal anhydroglucose rings. The intensity of band H increases greatly with decreasing DS and corresponds to the vibration of non-substituted OH groups at C2, C3 and C6 ring positions. The effect of DP on the OH stretching band is negligible, where DP equals the number of anhydroglucose units in the chain, at least in the range of DP values studied in this work.