Synthesis and Chiroptical Properties of Helical Polyallenes Bearing Chiral Amide Pendants

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• 作者：Yuan-Yuan Zhu ; Ting-Ting Yin ; Xue-Liang Li ; Ming Su ; Ya-Xin Xue ; Zhi-Peng Yu ; Na Liu ; Jun Yin ; Zong-Quan Wu
• 刊名：Macromolecules
• 出版年：2014
• 出版时间：October 28, 2014
• 年：2014
• 卷：47
• 期：20
• 页码：7021-7029
• 全文大小：503K
• ISSN：1520-5835

文摘

Two allene derivatives, l- and d-N-(1-(octylamino)-1-oxopropan-2-yl)-4-(propa-1,2-dien-1-yloxy)benzamide (l-1 and d-1), bearing chiral amide pendants were designed and synthesized. Living polymerizations of l-1 and d-1 with allylnickel complex as a catalyst afforded poly-l-1_m and poly-d-1_m with controlled molecular weights and narrow molecular weight distributions. These polymers were found to possess a stable helical conformation with a preferred handedness in aprotic solvents on the basis of their circular dichroism (CD) spectra and specific rotation as well as computer simulation. The helical conformation of the polymers was revealed to be stabilized by elongation of the repeating unit until the degree of the polymerization reaches 80. The slightly influence of temperature on the CD spectra of poly-l-1₁₀₀ in CHCl₃ indicated the helical conformation was quite stable at least in the range of 0鈥?5 掳C. Although poly-l-1₁₀₀ showed similar CD spectra in different aprotic solvents, remarkable decrease was observed upon the addition of protic solvents such as methanol due to the weakened hydrogen bonding interactions between the adjacent repeating units. The poly-l-1₁₀₀ behaves as a pH-responsive property; the helical structure of the main chain can be transformed to random coil by addition of trifluoroacetic acid to the THF solution which again switches back to helical conformation by neutralization with triethylamine. It was confirmed that the copolymerization of l-1 and d-1 obeyed the majority rule as supported by the nonlinear correlation between the enantiomeric excess of monomer 1 with the CD intensities of the generated copolymers. Atomic force microscope (AFM) and scanning electron microscope (SEM) studies revealed poly-l-1₁₀₀ self-assembled into well-defined helical fibrils with distinct handedness.