A glutamic acid-based polymer keeping intact the integrity of all the three original functionalities of the amino acid

Abstract

Dimethyl glutamate, on treatment with allyl bromide, afforded dimethyl N,N-diallylglutamate which upon alkaline ester hydrolysis followed by acidification with aqueous HCl gave N,N-diallylglutamic acid hydrochloride [(CH2=CH–CH2)2NH+CH(CO2H)(CH2)2CO2H Cl−] I. Using Butler’s cyclopolymerization protocol, new monomer I underwent ammonium persulfate-initiated polymerization to give pyrrolidine ring-embedded linear cyclopolymer II i.e. −[−CH2(C4H6)NH+{CH(CO2H)(CH2)2CO2H Cl−}CH2−]−n retaining the integrity of all the three functionalities of glutamic acid. Under the influence of pH, the repeating units of triprotic acid (+) in II were equilibrated to those of water-insoluble diprotic polyzwitterionic acid (±) III, water-soluble monoprotic poly(zwitterion-anion) (±−) IV, and its conjugate base polydianion (=) V. The critical salt concentration required to promote water solubility of (±) III has been determined to be 0.548 M NaCl, 0.271 M NaBr, 0.133 M NaI. The basicity constants of the carboxyl groups and trivalent nitrogen in (=) V have been determined. A 5 ppm and 20 ppm concentrations of III are effective in inhibiting the precipitation of CaSO4 from its supersaturated solution with a ≈100% scale inhibition efficiency at 40 °C for a duration of over 3 and 16 h, respectively.