Mass Spectrometry Research Group, Centre Interdisciplinaire de Spectrométrie de Masse (CISMa), University of Mons-Umons, 20 Place du Parc, 7000 Mons, Belgium.
J Mass Spectrom. 2011 Mar;46(3):237-46. doi: 10.1002/jms.1886.
Nowadays, numerous experimental and theoretical studies are devoted to the research field of polythiophenes and other electroconjugated polymers due to the huge potentialities of those conducting polymers. Synthetic procedures are now developed to reach the highest control over both polymerization and analytical methodologies allowing an in-depth and straightforward characterization of the polymer samples without any required doubt. Mass spectrometry methodologies and in particular MALDI-ToF measurements are definitively suitable to meet the characterization requirements. In the present study, trans-2-[3-(4-t-butyl-phenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) was shown to afford better results than the reported terthiophene and dithranol matrices as far as sensitivity and signal-to-noise ratio are concerned. We tentatively proposed that the ionization of the P3HT molecules is performed by charge exchange in the condensed phase (clusters) with matrix molecule radical cations and subsequent neutral matrix molecule evaporation from the clusters. The putative key parameters to account for the really high efficiency of DCTB for the MALDI analysis of P3HT are (1) the highest ionization energy of DCTB amongst the three matrices, (2) the really high absorptivity of the matrix molecule at the laser wavelength and (3) the presence of the tertiobutyl group on the matrix molecule. The presence of this substituent is likely to decrease the intermolecular interactions in the condensed phase rendering the evaporation of the neutral matrix molecules less energy demanding. We also demonstrated for polymer samples presenting an average number molecular weight (M(n) ) below 10 000 g mol(-1) that the systematic overestimation of the low mass oligomers upon MALDI measurements ends up with wrong M(n) and polydispersity index (PDI) values. A systematic Soxhlet extraction against heptane was shown to allow the recording of absolute M(n) and PDI.
如今，由于这些导电聚合物具有巨大的潜力，大量的实验和理论研究都致力于聚噻吩和其他电共轭聚合物的研究领域。现在已经开发出合成程序来实现对聚合和分析方法的最高控制，从而可以在无需任何疑问的情况下对聚合物样品进行深入和直接的表征。质谱方法，特别是 MALDI-TOF 测量，绝对适合满足表征要求。在本研究中，与报道的噻吩和二萘酚基质相比，反式-2-[3-(4-叔丁基-苯基)-2-甲基-2-丙烯基]丙二腈（DCTB）在灵敏度和信噪比方面显示出更好的结果。我们推测，P3HT 分子的电离是通过在凝聚相中（团簇）与基质分子自由基阳离子进行电荷交换，并随后从团簇中蒸发中性基质分子来进行的。DCTB 对于 P3HT 的 MALDI 分析具有非常高的效率，其可能的关键参数为：（1）三种基质中 DCTB 的电离能最高；（2）基质分子在激光波长处的高吸收率；（3）基质分子上存在叔丁基。该取代基的存在可能会降低凝聚相中分子间的相互作用，从而使中性基质分子的蒸发所需能量降低。我们还证明，对于平均分子量（M(n)）低于 10000g/mol 的聚合物样品，MALDI 测量中低质量低聚物的系统高估最终会导致错误的 M(n)和多分散指数（PDI）值。系统的索氏萃取（Soxhlet extraction）对庚烷的萃取证明可以记录绝对 M(n)和 PDI 值。
