Amino acid‐functionalized ethyl cellulose: Synthesis, characterization, and gas permeation properties

Amino acid esters of ethyl cellulose [R′ = H (1), CH3 (2), CH2CH(CH3)2 (3), CH2CONH2 (4), CH2OCH2C6H5 (5, 5′), CH2CH2CH2CH2NHOCOC(CH3)3 (6)] were synthesized in moderate to quantitative yields (30–99%) by the reaction of t‐butoxycarbonyl (t‐Boc)‐protected amino acids or an activated ester derivative with hydroxy groups of ethyl cellulose [EC; degree of substitution (DSEt), 2.69]. The amino acid functionalities displaying varied chemical nature, shape, and bulk were used, and bulk of the substituent on the α‐carbon of amino acids was elucidated to be of vital significance for the observed degree of incorporation (DSEst). 1H NMR spectra were used to determine the degree of incorporation of amino acid moiety (DSEst), and almost complete substitution of the hydroxy protons was revealed in 1, 2, and 5′. The onset temperatures of weight loss of 1–6 were 198–218 °C, indicating fair thermal stability. The glass transition temperatures of the derivatized polymers were 30–40 °C lower than that of EC (Tg 131 °C; cf. Tg of 1–6, 93.5–103 °C). Free‐standing membranes of EC and its amino acid esters (1, 2, 5, 5′, and 6) were fabricated, and enhanced permselectivity for CO2/N2 and CO2/CH4 gas pairs was discerned, when compared with EC.