一种基于聚噻吩-聚硒吩全共轭嵌段共聚物的合成及性质研究

Synthesis and Properties of an All-Conjugated PolythiophenePolyselenophene Diblock Copolymer

全共轭刚性-刚性嵌段共聚物兼具嵌段共聚物的微相分离特性和共轭聚合物的光电性能,引起了人们越来越多的关注.基于此,我们利用格氏置换(GRIM)方法合成了全共轭刚性-刚性嵌段共聚物聚(3-己基硒吩)-b-聚(3-(6-羟基)-己基噻吩)(P3HS-b-P3HHT).通过在噻吩段的烷基侧链末端引入羟基基团来丰富全共轭体系的溶液结构,并利用羟基的热交联特性提高聚噻吩均聚物的薄膜场效应晶体管的热稳定性.一方面,通过溶剂共混(氯仿/吡啶和甲醇/吡啶混合溶剂),调控P3HS-b-P3HHT分子在混合溶剂中的刚性-刚性相互作用,使P3HS-b-P3HHT在混合溶剂中自组装形成不同的纳米结构,如纳米带、纳米纤维和纳米微球等.另一方面,将P3HS-b-P3HHT和聚(3-己基噻吩)(P3HT)共混,利用羟基之间的热交联,使P3HS-b-P3HHT/P3HT共混薄膜在薄膜场效应晶体管中表现出较好的热稳定性.

All-conjugated rod-rod block copolymers（BCPs） have gained immense interest over the past few years because they combine fascinating self-assembly properties of BCPs with the optical and electronic properties of conjugated polymers. Based on it, an all-conjugated rod-rod BCPs, poly（3-hexylselenophene）-b-poly[3-（6-hydroxyl）hexylthiophene]（P3HS-bP3HHT） with hydroxyl groups as side substitution groups was synthesized via the Grignard metathesis（GRIM） method. The introduction of side hydroxyl groups was designed to endow different polarity between P3HS and P3HHT blocks and enrich the solution structures of P3HS-b-P3HHT. During thermal annealing, the cross-linking of hydroxyl groups was also utilized to improve the thermal stability of poly（3-hexylthiophene）（P3HT）-based organic field-effect transistors（OFETs） when blended with a certain amount of P3HS-b-P3HHT. On one hand, the use of mixed solvents provided an effective way to control the self-assembly behavior of P3HS-b-P3HHT. Depending on the mixed solvent ratio（i.e., chloroform/pyridine or methanol/pyridine）, the rod-rod interaction of the copolymer chains was controlled, yielding a series of nanostructures such as nanoribbons, nanofibers, and nanospheres. Detailed morphologies and the corresponding photophysical behavior of different nanostructures were characterized by transmission electron microscope and UV-vis absorption spectra. The conformations of the P3HS and P3HHT chains in the solutions influenced their photophysical properties greatly. On the other hand, based on the thermal cross-linkable properties of hydroxyl groups, a certain amount of P3HS-b-P3HHT was mixed with P3HT homopolymer to fabricate P3HS-b-P3HHT/P3HT OFETs. For control samples, the charge carrier mobility of pure P3HT-based OFETs was improved with the increased annealed temperatures up to 170 ℃, then decreased significantly when the temperature further increased to 200 ℃. While overall, the charge carrier mobilities of P3HS-b-P3HHT/P3HT OFETs were lower than those of pure P3HT-based OFETs, they were improved with the increased temperature to 200 ℃. It was found the P3HS-b-P3HHT（10%）/P3HT OFETs exhibited the charge carrier mobility of 0.040 cm2·V-1·s-1 after annealing at 200 ℃ for 1 h, which was higher than P3HT OFETs（0.025 cm2·V-1·s-1） under the same experimental condition. It was due to the cross-linking of hydroxyl groups in P3HS-b-P3HHT retain the crystallization structures of P3HT, thus improved the thermal stability of OFETs. Overall, this work demonstrates a new polythiophene-polyselenophene BCP with controlled nanostructures by solvent blending and promising application in OFETs to improve their thermal stability.