Chad Snyder - Quantifying Crystallinity in High Molar Mass Poly(3-hexylthiophene)

Document created by Chad Snyder on Aug 28, 2014Last modified by Chad Snyder on Aug 28, 2014
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  Publication Details (including relevant citation   information):

  C.R. Snyder, R.C. Nieuwendaal, D.M. DeLongchamp, C.K. Luscombe,   P. Sista and S.D. Boyd, Macromolecules  47, 3942-3950 (2014).


  We demonstrate a method to determine absolute crystallinity in   high molar mass poly(3-hexylthiophene) (P3HT), as used in   commercially relevant organic photovoltaic devices, using   enthalpy of fusion and melting temperature values derived from   differential scanning calorimetry (DSC) and 13C CPMAS   NMR. By studying P3HT with molar masses ranging from 3.6 to 49   kg/mol and using recent work on oligomeric 3-hexylthiophene, we   demonstrate several critical items. First, that proper   extrapolation to infinite chain lengths, i.e., crystal size,   yields values for the equilibrium melting temperature   Tm0 of 272 ± 6 °C and the enthalpy of   fusion per crystalline repeat unit ΔHu of 49 ± 2 J/g   for Form I crystals of P3HT. Second, that a simple correction for   crystal size using Tm0 is critical for   determining an accurate degree of crystallinity from enthalpy   measurements because of finite crystal size effects. Furthermore,   our results demonstrate that the ordered fraction of P3HT   measured from 13C NMR is indistinguishable from the   DSC-determined crystalline fraction, once crystal size   corrections are properly implemented. The connection between   crystal size and melting temperature is affirmed by successive   self-nucleation and annealing (SSA) measurements, which, when   performed as a function of molar mass, allowed us to identify the   molar mass at which chain folding occurs in P3HT in the melt,   ≈11.5 kg/mol.


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