Spectroscopic and Molecular Weight Studies of Polytoluidines
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SPECTROSCOPIC AND MOLECULAR WEIGHT STUDIES OF POLYTOLUIDINES Y. Wei,* K. F. Hsueh and S. Nagy Department of Chemistry, Drexel University, Philadelphia, PA 19104 A. Ray, A. G. MacDiarmid and J. Dykins Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323 A. J. Epstein Departments of Chemistry and Physics, Ohio State University, Columbus, OH 43210 G. E. Wnek Department of Chemistry, Rensselaer Polytechnic Institute, Troy, NY 12180 ABSTRACT Poly(o-toluidine) and poly(m-toluidine) in base form have been characterized by infrared and lH NMR spectroscopy. Assignments of the proton NMR signals have been facilitated by the use of model compounds. The distinction between benzenoid and quinoid methyl resonances in the NMR permits a semi-quantitative estimation of the oxidation states of the polytoluidines. Infrared studies are consistent with a polyaniline-type backbone having pendant methyl groups. Field desorption mass spectrometry (FD-MS) was employed for estimation of the molecular weight of poly(o-toluidine). Gel-permeation chromatography of the same sample showed a bimodal elution pattern, suggesting that the FD-MS technique detects only the lower molecular weight fraction of the polymer. Despite this inherent limitation, FD-MS yields the interesting information that the polymer contains chains of both odd and even numbers of repeat units, necessitating the coexistence of different oxidation states in the base form of the polymer. INTRODUCTION Recently, there have been many reports on the synthesis, electrochemistry and electronic properties of alkyl ring-substituted polyanilines.[1-3] Like the unsubstituted polyaniline, these polyaniline derivatives also exhibit reasonably high electrical conductivities upon doping with protonic acids, well-behaved electrochemistry and good environmental stability. Furthermore, their solubilities in organic solvents were found to be generally higher than that of polyaniline.[1,21 However, very few studies have been reported on the structural characterization and the molecular weights of these polymers. It is proposed that the structures of these polymers in their base (undoped) form could be represented by the following general formula:
Rf
R
R
RHd N
where R is H for polyaniline, CH 3 for polytoluidines, and CH3 CH 2 for polyethylanilines, etc. The value of y represents the oxidation state of the polymers, which could be estimated by elemental analysis or by chemical titrations.[4] The polymers are in the "pernigraniline", "emeraldine" and "leucoemeraldine" oxidation states when y has values of 0, 0.5 and 1.0, respectively. In this communication, we report the spectroscopic and molecular weight studies of the base form of poly(o-toluidine), poly(m-toluidine) and poly(o-ethylaniline), by means of infrared, proton NMR, and field desorption mass spectroscopy (FD-MS), and by gelpermeation chromatography (GPC).
Mat. Res. Soc. Symp. Proc. Vol. 173. ©1990 Materials Research Society
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EXPERIMENTAL
The polymers were synthesized by oxidation of the appropri
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