Effect of Regioregularity on the Semicrystalline Structure of Poly(3-hexylthiophene)
Effect of Regioregularity on the Semicrystalline Structure of Poly(3-hexylthiophene)
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DOI：
10.1021/ma201604n
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发表时间：
2011-09-27
期刊：
影响因子：
5.5
通讯作者：
DeLongchamp, Dean M.
中科院分区：
文献类型：
--
作者：
Snyder, Chad R.;Henry, Jessica S.;DeLongchamp, Dean M.
聚（3-己基噻吩-2，5-二基）（P3 HT）是一种研究广泛的聚合物，因为其在可印刷电子和光伏器件中的潜在用途。最初，P3 HT仅以通过氧化聚合制成的低区域规整性形式存在，很少表现出高电荷迁移率。在20世纪90年代，新的合成技术使得能够生产受控的、高区域规整性的材料，这些材料表现出显着增加的电荷迁移率。1虽然改进的区域规则性控制是一项重要的创新，但尚未系统评估P3 HT的区域缺陷对晶体片层厚度、结晶度和结晶动力学的可量化影响。与其他材料（如全同立构聚丙烯2015（iPP）或DL-聚交酯6，7）一样，区域或立体缺陷的存在使其有效地成为共聚物。(In P3 HT，有效的共聚物单元是头-尾（HHT）、头-头（HHT H）或尾-尾（THT）偶联。在结晶过程中，缺陷将从晶体中排除，或者如果掺入晶体中，则将受到结晶损失。正如克里斯特所指出的，8这种材料（共聚物）的行为将不同于无缺陷的均聚物，因为（1）层状厚度（即，链轴晶体学方向）也将通过可结晶的无缺陷链段的长度分布而不是仅仅通过动力学成核障碍来决定，并且（2）结晶过程涉及熵项，这是由于纯的可结晶段在熔体中与具有缺陷的那些段分层。片层厚度对P3 HT 9的电子性质具有关键影响，因为其定义为平行于聚合物主链的晶畴尺寸，这被认为是电荷载流子的最快传输方向。10对于P3 HT，H3 OH缺陷导致链中的“扭结”（参见图1）。很可能，这种扭结将被拒绝从P3 HT晶体，或者，如果纳入，将有一个相当大的自由能处罚。例如，iPP中只有22%的区域缺陷包含在晶体中。[4]缺陷在非晶区的强烈分布将强调控制P3 HT中区域规则性的重要性。如将证明的，其对结晶和熔融的影响是显著的，足以要求P3 HT样品或器件的感兴趣的性质根据区域规则性的程度来框定。例如，93%、96%和98%的区域规则P3 HT不能被视为相同的，并且它们之间的差异可以被确定。在这里，我们证明了一系列不同的区域规整性P3 HT聚合物的熔融行为的趋势定性地遵循Flory平衡共聚物理论11的预测，如由Crist和同事修改的8，12，13（FCT）。此外，我们使用这个框架来证明区域规整性限制最终的晶体片层厚度的影响。为了简单起见，并根据几何扰动引起的一个HCHH缺陷，我们将自己限制到一个模型的基础上完全排除的缺陷从晶体。
Poly (3-hexylthiophene-2, 5-diyl)(P3HT) is a widely studied polymer because of its potential use in printable electronics and photovoltaic devices. Initially, P3HT was available only in lowregioregularity forms made by oxidative polymerization that rarely exhibited high charge mobility. In the 1990s, new synthetic techniques enabled the production of controlled, high-regioregularity materials that exhibited significantly increased charge mobility. 1 Although improved control over regioregularity was an important innovation, there has not been a systematic evaluation of the quantifiable impact of P3HT’s regiodefects on crystal lamellar thickness, crystallinity, and crystallization kinetics. As is the case for other materials such as isotactic polypropylene2À5 (iPP) or DL-polylactides, 6, 7 the presence of a regio or stereo defect makes it effectively a copolymer.(In P3HT, the effective copolymer units are headÀtail (HÀT), headÀhead (HÀH), or tailÀtail (TÀT) couplings.) During crystallization, the defects will either be excluded from the crystal or will be subject to an enthalpic penalty if incorporated into the crystal. As pointed out by Crist, 8 such a material (copolymer) will behave differently from a defect-free homopolymer in that (1) the lamellar thickness (ie, chain axis crystallographic direction) will also be determined thermodynamically by the length distribution of crystallizable defect-free segments rather than solely by kinetic nucleation barriers and that (2) the crystallization process involves an entropic term due to demixing in the melt of pure crystallizable segments from those segments possessing defects. The lamellar thickness has a critical impact on the electronic properties of P3HT9 because it is by definition the crystal domain size parallel to the polymer backbone, which is thought to be the fastest transport direction for charge carriers. 10 For P3HT, HÀH defects result in a “kink” in the chain (see Figure 1). It is likely that such a kink would be rejected from the P3HT crystal, or, if incorporated, there would be a considerable free energy penalty. For example, only 22% of the regiodefects in iPP are included in the crystal. 4 Strong partitioning of defects into the noncrystalline regions would underscore the importance of controlling regioregularity in P3HT. As will be demonstrated, its impact on crystallization and melting is significant enough to require properties of interest for P3HT samples or devices to be framed in terms of the degree of regioregularity. For example, 93%, 96%, and 98% regioregular P3HTs cannot be treated as identical, and the differences between them can be determined. Here, we demonstrate that the trend in melting behavior for a series of different regioregularity P3HT polymers follow qualitatively the predictions from Flory’s equilibrium copolymer theory11 as modified by Crist and co-workers8, 12, 13 (FCT). Additionally, we use this framework to demonstrate the effect of regioregularity on limiting ultimate crystal lamellar thickness. For simplicity, and based on the geometric perturbation induced by a HÀH defect, we are limiting ourselves to a model based on complete exclusion of the defect from the crystal.