Controlled Dehydrochlorination of Poly(vinyl chloride) for Fabrication of Membranes with Polyacetylene-Like Structure: XPS Analysis and Ion Exchange Membrane Discussion

Poly(vinyl chloride) (PVC) can be dehydrochlorinated by strong bases, e.g. tert-butoxide and hydroxide, to attain polyacetylene-like highly conjugated polymer chains. Dehydrochlorinated PVC (DHPVC) can be further functionalized by additional reactions to obtain ion exchange membranes, battery membranes, semiconductors, etc. However DHPVC resin is not available for membrane casting because of its low solubility. Therefore dehydrochlorination was performed directly on PVC membranes in this research. The extent of dehydrochlorination and the length of conjugation were controlled by adjusting conditions such as base/PVC ratio and solvent type. X-ray photoelectron spectrometry and elemental analysis were used to detect Cl, C, O, and H contents of the products. A calculation method that uses parameters of atomic approximations, was proposed to mathematically express trends of “degrees of dechlorination, dehydrochlorination, unsaturation, and substitution” with respect to the amount of base used. Up to 64.5% unsaturation and 96.6% dechlorination of PVC membranes were achieved. In addition, theoretical ion exchange capacity (IECtheo) was defined with a suggestion that charged functional groups can be attached to the polymer backbone by double bonds, allowing ion exchange membranes to be manufactured. By tailoring the degree of unsaturation in dehydrochlorinated species, theoretically up to 18 meq/g of IEC would be reached if all double bonds would be functionalized. Scanning electron microscopy analysis showed that tert-butoxide products had a porous structure. FTIR and UV-Visible spectroscopy results verified the formation of long polyene sequences. Dehydrochlorination may be a legitimate method for recycling PVC waste into functional membrane materials.