Poly(acrylonitrile) ultrafiltration membranes. I. Polymer‐salt‐solvent interactions

Abstract

Abstract Fourier transform infrared spectroscopy was used to study the interactions among LiCl, ZnCl 2 , and AlCl 3 with N , N ‐dimethylformamide (DMF) and poly(acrylonitrile) (PAN). It was observed that all three salts complex with DMF as well as PAN. The strength of the cation interaction with the >CO oxygen of DMF was found to be higher than that with the CN group of PAN. The >CO stretching frequency of DMF with ZnCl 2 was red shifted, indicating stronger complex formation compared with other two cations. With the addition of salt, the salt–DMF pseudo solvent was found to become a θ solvent for PAN compared with neat DMF. This change in PAN solvation power was primarily the result of DMF–salt complexation. As a result of the complexation, Mark‐Houwink constant a , was found to reduce from 0.75 (for pure DMF) to ∼0.6 for DMF–salt solvents, indicating decreased PAN chain expansion. Comparison of intrinsic viscosity [η] values indicated that addition of salts to PAN–DMF solutions resulted in: (i) decrease in the DMF solvation power, which causes less expanded polymer coils, and (ii) increased interpolymer chain entanglements via salt‐promoted chain association. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2061–2073, 2005