Effect of halogen substituents on polymer membrane hydrophobicity, swelling and transport mechanism: chlorine versus fluorine

Abstract

While the role of fluorine on mass transport in polymers has been the subject of extensive research efforts, less attention has been paid to the role played by other halogens, such as chlorine. These efforts favored the synthesis of a plethora of perfluoropolymers which, although exhibiting enhanced physical aging resistance relative to conventional hydrocarbon-based polymers, suffer from swelling and plasticization in the presence of hydrocarbons.In this study, we show that the presence of chlorine in perfluoropolymers alters their hydrophobicity while enhancing swelling resistance and size-sieving ability. Model polar vapors, such as methanol and water, and non-polar hydrocarbon vapors were selected for a fundamental transport study in a series of co-polymers of perfluoro(2-methylene-4-methyl-1,3-dioxolane (PFMMD) and chlorotrifluoroethylene (CTFE), namely poly(PFMMD-co-CTFE), exhibiting systematically varied molar amount of CTFE (i.e., chlorine). Fundamental structure-property correlations were developed and possible applications in the field of membrane separations were outlined. Finally, a series of solubility data of chlorinated fluids in polar liquids was discussed to support our conclusions.