Wong Michael, Hollinger Jon, Kozycz Lisa M, McCormick Theresa M, Lu Yijie, Burns Darcy C, Seferos Dwight S
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada.
ACS Macro Lett. 2012 Nov 20;1(11):1266-1269. doi: 10.1021/mz300333f. Epub 2012 Oct 12.
We report the linear and nonlinear regions of the relationship between number average molecular weight determined by gel permeation chromatography (GPC) and H NMR end-group analysis for a series of -tolyl-initiated poly(3-hexylthiophene)s (P3HTs). For conjugated polymers with chains that are 39-138 repeat units in length (6.5-23 kDa), GPC systematically overestimates the number average molecular weight () by a factor of 1.3 ± 0.1 (standard error), and GPC and H NMR end-group analysis correlate in a linear manner. For chains 138-1130 (23-188 kDa) repeat units in length, we observe a nonlinear relationship between GPC and end-group analysis. Static light-scattering experiments confirm that at high molecular weight (>70 kDa) decreasing the catalyst loading does not appreciably increase the polymer chain length. Thus, we conclude that there is a molecular weight limit in the synthesis of externally initiated polythiophenes and a propensity for the growth of nonexternally initiated chains which increases as a function of . This is significant as external initiation has been reported to result in nearly 100% externally initiated chains as well as reduce the possibility of chain-chain coupling in a typical synthesis. Our data show that 100% external initiation only holds true for polymers that are less than 40 kDa and encourages caution when determining by NMR using this synthetic methodology at high molecular weights.
我们报告了一系列由对甲苯基引发的聚（3-己基噻吩）（P3HT）通过凝胶渗透色谱法（GPC）测定的数均分子量与¹H NMR端基分析之间关系的线性和非线性区域。对于链长为39 - 138个重复单元（6.5 - 23 kDa）的共轭聚合物，GPC系统性地将数均分子量（Mn）高估了1.3 ± 0.1倍（标准误差），并且GPC和¹H NMR端基分析呈线性相关。对于链长为138 - 1130（23 - 188 kDa）个重复单元的聚合物，我们观察到GPC与端基分析之间存在非线性关系。静态光散射实验证实，在高分子量（>70 kDa）时，降低催化剂负载量并不会显著增加聚合物链长度。因此，我们得出结论，在外部引发的聚噻吩合成中存在分子量限制，并且存在非外部引发链增长的倾向，这种倾向会随着Mn的增加而增加。这一点很重要，因为据报道外部引发会导致几乎100%的外部引发链，同时在典型合成中降低链 - 链偶联的可能性。我们的数据表明，100%外部引发仅适用于分子量小于40 kDa的聚合物，并且在使用这种合成方法通过NMR测定高分子量聚合物的Mn时需谨慎。
