t-Butylcarbamates of ethyl cellulose (1: DSEt, 2.69; 2: DSEt, 2.50) and cellulose acetate (3: DSAc, 2.46; 4: DSAc, 1.80) were synthesized by the reaction of residual hydroxy groups of cellulose derivatives with t-butylisocyanate. The H-1 NMR spectra and elemental analysis were employed to determine the degree of incorporation of carbamoyl moiety (DSCarb) and almost complete Substitution of the residual hydroxy protons was observed. The presence of the peaks characteristic of the carbamate linkage in the FTIR spectra furnished further evidence for the successful carbamoylation of ethyl cellulose and cellulose acetate. The resulting polymers (1a-4a) were soluble in common organic solvents. The onset temperatures of weight loss of 1a-4a were 177-204 degrees C, indicating fair thermal stability. The free-standing membranes of 1-4 and 1a-4a were fabricated, and derivatized polymers exhibited enhanced gas permeability, especially the gas permeability of cellulose acetate (3: DSAc, 2.46; 4: DSAc, 1.80) underwent a significant increment. 4a exhibited a remarkable increase in CO2 permeability, i.e., 22 times higher than that of 4 (P-CO2 38 barters; cf. P-CO2 of 4, 1.7 barrers). Quite interestingly, a more or less retainment of CO2/N-2 permselectivity was revealed. (C) 2008 Elsevier B.V. All rights reserved.