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ABSTRACT
4-Maleimidobenzoic acid (MBA) was explored as a comonomer in polyacrylonitrile (PAN) precursors for carbon fiber. The copolymerization of acrylonitrile (AN) with MBA was carried out in DMF. The reactivity of MBA was considerably less than that of AN, which was manifested as a negative reactivity ratio for the former. The r MBA- values from −0.24 to −0.33 and r AN values of 1.07 were obtained by Kelen-Tudos and extended Kelen-Tudos methods. The penultimate reactivity ratios were determined by both linear and non-linear methods. The values were r 1=0.0093, r 1′=0.0132, r 2=1.063 and r 2′=1.625. The relative MBA concentration in the copolymer decreased drastically on enhancing its content in the monomer mixture. The penultimate model could satisfactorily explain the feed-copolymer composition profile for the whole composition range. MBA caused a decrease in the apparent copolymerization rate and molecular weight in agreement with the observed trends in the reactivity ratios. A statistical prediction of monomer sequences based on reactivity ratios implied that MBA existed as a lone monomer unit between the long sequences of AN units. This sequence distribution is suited for the efficiency of MBA in cyclisation reaction, which stabilizes PAN during its pyrolysis. Optimum thermal stabilization effect and char yield were observed for copolymers with around 3 mol% MBA in the chain.
ACKNOWLEDGMENTS
The permission granted by Director, VSSC to publish the paper is gratefully acknowledged. Mr. V. P. Balagangadharan is thanked for his help in performing the GPC analysis and Mrs. B. K. Catherine for the thermal analysis. One of the authors (RD) thanks the University of Kerala for awarding a fellowship.