Synthesis and Catalytic Properties of Polysiloxane Bearing 3-Sulfopropyl Groups

Abstract

Poly[(3-sulfopropyl)siloxane]s [4] were synthesized by sulfonating in aqueous solution of Na₂S0₃ the corresponding poly[(3-bromopropyl)siloxan14]s [3], which were obtained b y copolymerizing (C₂H₅0)₃Si(CH₂)₃Br [1 ] and (C₂H₅SO)₄Si [2] with molar ratio, n(=[1]/[1]+[2]), of 0.1-0.5. Among the polysiloxanes [4 ], those with n=0.2 and 0.3 were solids with acidity of 1.0 and 1.3 mmol. g-1, respectively. The catalytic activities of the two polysiloxanes [4] for an acid-catalyzed reaction and their thermal stabilities were examined.
In the vapor-phase conversion of ethanol, dehydration reaction proceeded to yie ld mainly diethyl ether at 453 K; the ethanol conversion was 87% (n=0.2) or 70% (n=0.3), and the activities were stable for 1-4 h of on-stream time. Thermal treatment of the polysiloxanes 4] at 543 K for 12 h under a nitrogen stream had little effect on the catalytic [acitivity for the dehydration of C2H5OH; the thermal stability of [4] is higher than an anion-exchange resin, Amberlyst-15. The p olysiloxanes [4] showed a catalytic activity also for the liquid-phase esterification of acetic acid with isobutyl alcohol. During the esterification, catalytically active components of [4] were little eliminated from the polysiloxane linkage.