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

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 4 h period of peak solar insolation, the bromination yield of a 1.18 m×0.12 m strip of IPF (Pp-MS content, 31.88% w/w; film thickness, 80±11 µm) 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±0.04 meqg−1, bulk resistivity of 4.52±0.47 Ω m, 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.