Phase Separation in the Melt and Confined Crystallization as the Key to Well-Ordered Microphase Separated Donor鈥揂cceptor Block Copolymers

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• 作者：Ruth H. Lohwasser ; Gaurav Gupta ; Peter Kohn ; Michael Sommer ; Andreas S. Lang ; Thomas Thurn-Albrecht ; Mukundan Thelakkat
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：June 11, 2013
• 年：2013
• 卷：46
• 期：11
• 页码：4403-4410
• 全文大小：426K
• 年卷期：v.46,no.11(June 11, 2013)
• ISSN：1520-5835

文摘

Microphase-separated donor鈥揳cceptor block copolymers have been discussed as ideal systems for morphology control in organic photovoltaics. Typical microphases as known from coil鈥揷oil systems were not observed in such systems due to crystallization dominating over microphase separation. We show how this problem can be overcome by the synthesis of high molecular weight block copolymers leading to a high enough 蠂N parameter and microphase separation in the melt. A combination of copper-catalyzed azide-alkyne click reaction and nitroxide mediated radical polymerization (NMRP) was used for the synthesis of donor鈥揳cceptor poly(3-hexylthiophene)-block-poly perylene bisimide acrylate (P3HT-b-PPerAcr) block copolymers. With this synthetic strategy, high molecular weights are possible and no triblock copolymer byproducts are formed, as observed with former methods. Two different block copolymers with a high molecular weight P3HT block of 19.7 kg/mol and a PPerAcr content of 47 and 64 wt % were obtained. X-ray scattering measurements show that the diblock copolymers exhibit microphase separation in the melt state. Furthermore, upon cooling confined crystallization occurs inside the microphase separated domains without destroying the microphase order. The observed microstructures fit well to the respective volume fractions and the crystalline packing within the individual blocks is analogous to those in the respective homopolymers. For the first time, typical lamellar or cylindrical phase separated structures as known for amorphous coil鈥揷oil systems are realized for a crystalline鈥搇iquid crystalline, donor鈥揳cceptor block copolymer. A similar block copolymer synthesized with an earlier method exhibits a crystallization-induced microphase separation.