Probing the Polarity of Various Cellulose Derivatives with Genuine Solvatochromic Indicators

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‐dichloroethane (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. Formulas of the probe molecules used. magnified image Formulas of the probe molecules used.