Chemical modification of poly(substituted-acetylene): II. Pervaporation of ethanol / water mixture through poly(1-trimethylsilyl-1-propyne) / poly(dimethylsiloxane) graft copolymer membrane

Poly(1-trimethylsilyl-1-propyne)/poly(dimethylsiloxane) (PTMSP/PDMS) graft copolymer was prepared to evaluate the permeation characteristic at pervaporation of aqueous ethanol solution through the graft copolymer membrane. For the preparation of PTMSP/PDMS graft copolymer, an improved synthetic procedure was released in this paper, which comprised a one-pot reaction of PTMSP in lithium bis(trimethylsilyl)amide followed by treatment with hexamethylcyclotrisiloxane and trimethylchlorosilane. PDMS content of the graft copolymer was controlled in the range 5–74 mol%. Very tough and thin membranes could be prepared from these copolymers having various PDMS content by the solvent casting method. The permselectivity of the membranes was investigated by pervaporation of ethanol/water mixture at 30°C. Preferential permeation of ethanol was observed for the membranes. It was also found that the selectivity of every copolymer membrane was higher than that of the PTMSP membrane. Moreover, the selectivity depended on the PDMS content of the graft copolymer. The separation factor and permeation rate assumed the maximum values at 12 mol% PDMS content. At the maximum point, 7 wt% aqueous ethanol solution was concentrated to about 70 wt% ethanol solution, and the separation factor and permeation rate were 28.3 and 2.45 × 10−3g · m/m2 · h, respectively. Such a high permselectivity for ethanol might be due to a delicate alteration of membrane structure, which was induced by the introduction of a short PDMS side chain into a PTMSP backbone.