Vapor-phase synthesis of poly( p -xylylene) membranes for gas separations

Abstract We report a vapor-phase deposition of poly( p -xylylene) (parylene) membranes for gas separations. Three parylene membranes, poly[(2-chloro- p -xylylene)] (parylene C), poly[(4-amino- p -xylylene)- co -( p -xylylene)] (parylene A), and poly[(2-carboxylic acid N-hydroxysuccinimide ester)- co -( p -xylylene)] (parylene NHS ester), were evaluated. These membranes were deposited on a support of porous poly(vinylidene fluoride) with a dense layer of poly(vinyl alcohol) cast on its top surface. The as-synthesized parylene membranes were characterized by scanning electron microscopy, FT-IR spectroscopy, and the measurements of water contact angle. Single-gas permeation with hydrogen, nitrogen, methane, and carbon dioxide was performed on the parylene membranes for assessing their molecular transport properties. These parylene membranes showed gas permeability of up to hundreds of barrer. To further enhance the gas separation performance of the parylene membranes, polyethylenimine (PEI) was used for modifying the surface of the membranes composed of parylene NHS ester.