Biological and Soft Systems, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK.
J Am Chem Soc. 2012 Mar 14;134(10):4790-805. doi: 10.1021/ja210871j. Epub 2012 Mar 5.
Identifying structure formation in semicrystalline conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between physical properties, structure formation, and device parameters of regioregular, semicrystalline poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and molecular weight. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl(2) as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group analysis and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different molecular weights is synthesized via new, soluble nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering experiments, allow the development of a simple model for estimating the degree of crystallinity. We find very good agreement for predicted and experimentally determined degrees of crystallinities as high as ∼70%. For Ni(dppp)Cl(2)-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter determining crystallinity within the molecular weight range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicrystalline conjugated polymers as well.
确定半结晶共轭聚合物中的结构形成是理解这些材料中电子过程的基础。尽管已经建立了规则性、半结晶聚 3-己基噻吩（P3HT）的物理性质、结构形成和器件参数之间的相关性，但仍然难以区分规则性、多分散性和分子量的影响。在这里，我们表明，最常用的 P3HT 合成方法，即使用 Ni(dppp)Cl2 作为催化剂的活性质子转移聚缩合（KCTP），导致具有单个尾对尾（TT）缺陷的规则性链分布在整个链上，与迄今为止假设的仅在链端的位置相反。NMR 端基分析和模拟用于定量这种效应。通过新的、可溶性镍引发剂合成了一系列具有不同分子量的完全无缺陷 P3HT 材料。通过各种量热和散射实验阐明的无缺陷 P3HT 中的结构形成数据，允许开发一种简单的模型来估计结晶度。我们发现预测和实验确定的结晶度之间非常吻合，高达约 70%。对于由一个分布的 TT 单元组成的 Ni(dppp)Cl2 引发的链，模拟结晶度与量热和光学测量的比较强烈表明 TT 单元被纳入晶格，这伴随着主链扭转的增加。多分散性被确定为在所研究的分子量范围内决定结晶度的主要参数。我们相信，所提出的方法和结果不仅有助于理解 P3HT 中的结构形成，而且通常也适用于其他半结晶共轭聚合物。
