The NMR Spectrum of Poly(3-alkylthiophene)s and Polymer Chain Configuration

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Abstract
The α-methylene 400 MHz NMR spectra of poly(3-alkylthiophene)s for n=5, 8 and 10, where n is the number of carbon atoms of the alkyl chain, are used to obtain information on the relative configurations of thiophene rings. The triplet α-CH2 peak of the monomer results in two peaks in the polymer. Highly sterically hindered α-CH2 yields a downfield NMR shift for coplanar rings. This steric hinderance results in markedly torsioned thiophene rings which yield an upfield-shifted α-CH2 peak. The relative peak intensity ratios indicate ∼25% highly torsioned rings for n=5 and 8, and about ∼50% torsioned rings for n=10.