Ryan C. Nieuwendaal
We outline the details of acquiring quantitative 13C cross-polarization magic angle spinning (CPMAS) NMR spectra on the most ubiquitous polymer for organic electronics (OE) applications, poly(3-hexylthiophene) (P3HT), despite other groups’ claims that CPMAS of P3HT is strictly non-quantitative. We lay out the optimal experimental conditions for measuring crystallinity in P3HT, which is a parameter that has proven to be critical in the electrical performance of P3HT-containing OPVs, but remains difficult to measure by scattering\/diffraction and optical methods despite considerable efforts. Herein, we overview the spectral acquisition conditions of the two P3HT films with different crystallinities from our previous study (R. C. Nieuwendaal, C. R. Snyder, D. M. DeLongchamp, ACS Macro. Lett., 2014, 3, 130-135). We point out that that due to the chemical similarity of P3HT to other alkyl side chain, highly conjugated main chain polymers, our protocol could straightforwardly be extended to other OE materials. Variable temperature 1H NMR results are shown as well, which (1) yield insight into the molecular dynamics of P3HT, (2) add context for spectral editing techniques as applied to quantifying crystallinity, and (3) show why T1H is a more optimal relaxation filter for distinguishing between crystalline and non-crystalline phases of highly-conjugated, alkyl side chain polymers than other relaxation times such as T2H and T1xzH.