Sustainable synthesis of a high performance inter-polymer anion exchange membrane employing concentrated solar radiation in a crucial functionalization step

Abstract

Preparation of an anion exchange membrane (AEM) from polymethylstyrene-co-divinylbenzene/polyethylene (Pp-MSt-co-DVB/PE) inter-polymer film (IPF) was reported recently. Functionalization of the above IPF was achieved through photo-thermochemical benzylic bromination with N-bromosuccinimide. The end result was the same as that achieved through chloromethylation of conventional styrene-DVB IPF, while avoiding use of carcinogenic chloromethyl ether. The present study reports the optimum process for preparation of the Pp-MSt-co-DVB/PE IPF and a new protocol for its efficient bromination employing concentrated solar radiation. No chemical initiator was necessary in the new process. Over the 4h period of peak solar insolation, the bromination yield of a 1.18m×0.12m strip of IPF (Pp-MS content, 31.88% w/w; film thickness, 80±11µm) was 87.1±3.5%. Cross-sectional analysis showed reasonable uniformity of bromination across the film thickness. The AEM obtained upon quaternization exhibited an anion exchange capacity of 1.60±0.04meqg−1, bulk resistivity of 4.52±0.47Ωm, and chloride transport numbers (EMF method) of 0.941±0.003 and 0.981±0.002 employing HCl and NaCl, respectively, as electrolytes. The performance of the synthesized AEM was compared with that of IONSEP-HC-A, a commercial AEM.