SYNTHESIS OF NOVEL BENZIMIDAZOLIUM PERFLUORO MODEL COMPOUNDS USING FREE RADICAL REACTIONS AND SYNTHESIS OF NOVEL LIGANDS SUBJECT TO BOTH FREE RADICAL AND ROMP POLYMERIZATION REACTIONS FOR FABRICATING ANION-EXCHANGE MEMBRANES
Date of Award
Master of Science
In the first part of this thesis, three different structures of perfluoro-benzimidazolium polymers were designed. Three benzimidazole model compounds were also designed to mimic the actual membranes. The three model compounds were synthesized via multiple steps and connected with fluorine tags via free radical based reactions. The first one is 1,3-dimethyl-2-phenyl benzimidazole with two methyl protecting groups on the phenyl ring; the second one is 1,3-dimethyl-2-phenyl benzimidazole with two phenyl protecting groups on the phenyl ring; and the third one is 2-phenyl benzimidazole with no protecting group on the phenyl ring as a reference. A new model reaction was developed to bond benzimidazolium ligands with perfluorohexyl iodine. The free radical substitution used Cp2Fe and H2O2 as a radical initiator under a mild condition. The stability of those model compounds under alkaline condition (3 M NaOD/MeOD/D2O at 80 °C) can be tested using NMR methods. In the second part of the thesis, a novel AIBN-norbornene structure was synthesized and used as a free radical initiator for polymerization of pentafluoroethyl trifluoro vinyl ether to yield a perfluoro chain with a norbornene structure at the end. The norbornene structure provides a position for further polymerization with Grubbs catalyst and cyclooctene-triphenyl-phosphonium salt. Under Grubbs second generation catalyst, both rings on norbornene side and cyclooctene side were undergone ring-opening metathesis polymerization to form a long hydrocarbon chain. The positively charged triphenyl-phosphonium group serves as an anion-exchange group for better conductivity. Then, all the double bonds on polymer were reduced by hydrogenation and form a half hydrocarbon half perfluoro polymer. This type of hybrid polymer can be combined with PTFE to provide better mechanical strength and water uptake. The bulky anion exchange group also expect to provide alkaline stability.
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