Probing the polarity of various cellulose derivatives with genuine solvatochromic indicators

Abstract

Kamlet-Taft's α(hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity) and π*(dipolarity/polarizability) values of carboxymethyl celluloses (CMCs) and cellulose tosylates (CTs) with different degrees of substitution are reported. Fe(phen)2(CN)2[cis-dicyanobis(1,10-phenanthroline) iron(II)] (1), Michler's ketone [4,4′-bis(N,N-dimethylamino)benzophenone] (2), and 4-aminobenzophenone (3) have been used as solvatochromic surface polarity indicators. The three probes 1, 2, and 3, respectively, have been adsorbed onto polymer samples from 1,2-dichloro-ethane (1) and cyclohexane (2, 3) solution for the UV/Vis measurements. The probe-loaded samples have been measured by means of a special reflectance technique. Apparent ET(30) values are calculated by applying linear solvation energy relationships (LSER) using the independently determined α and π*values of the samples according to ET(30) = [ET(30)]0 + aα + sπ*, because ET(30) values are not directly available for these materials. α values of CMCs and CTs significantly decrease with increasing degree of substitution due to the decrease of the number of cellulosic OH groups (Cell-OH). The dipolarity/polarizability π*values of the CMCs show no linear dependence on the degree of substitution. A slight increase of π* with DS is observed for CTs. The β term using 3 as the probe for CTs is not determinable, because 3 also interacts, via the carbonyl oxygen, with acidic sites of the cellulose OH groups.