Synthesis, characterization, and gas permeation properties of the silyl derivatives of cellulose acetate

Silylation of cellulose acetate having different acetyl contents (1: DSAc = 1.80 and 2: DSAc = 2.46) was carried out by the reaction of various chlorosilanes [R = SiMe3 (a), SiEt3 (b), SiMe2C8H17 (c), SiMe2C18H37 (d), SiMe2Ph (e)] with remaining hydroxy groups of cellulose acetate, and complete substitution was confirmed by 1H NMR and FT-IR spectroscopy. All of the silylated derivatives (1a–e and 2a–e) were soluble in common organic solvents and displayed enhanced solubility in relatively non-polar solvents. The onset temperatures of weight loss of 1a–e and 2a–e were higher than 220 °C, indicating fair thermal stability. Silylation of 1 and 2 accompanied a decrease in glass transition temperature, and the decrease became more pronounced as the length of alkyl chain in the silyl group increased. Free standing membranes of 1a–e and 2a–e could be fabricated, and the silylated derivatives displayed remarkably improved gas permeability as compared to 1 and 2. Incorporation of longer silyl groups was more effective to enhance gas permeability, for instance, the P values of 1c were the highest, and its PCO2PCO2 (160 barrers) was 94 times higher than that of 1. The PCO2/PN2PCO2/PN2 of the silylated polymers (1a–e and 2a–e) was appreciably large (19–36), and the values for 1a–c, 2a, and 2c were located either on the upper bound or above it in the plot of permselectivity versus permeability for the CO2/N2 gas pair.