Tabei Junichi, Shiotsuki Masashi, Sato Takahiro, Sanda Fumio, Masuda Toshio
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura Campus, Japan.
Chemistry. 2005 Jun 6;11(12):3591-8. doi: 10.1002/chem.200401009.
N-Propargylbenzamides 1-7 were polymerized with (nbd)Rh(+)[eta(6)-C(6)H(5)B(-)(C(6)H(5))(3)] to afford polymers with moderate molecular weights (M(n) = 26,000-51,000) in good yields. The (1)H NMR spectra demonstrated that the polymers have fairly stereoregular structures (81-88 % cis). The optically active polymers, poly(1) and poly(2), were proven by their intense CD signals and large optical rotations to adopt a stable helical conformation with an excess of one-handed screw sense when heated in CHCl(3) or toluene. The sign of Cotton effect could be controlled by varying the content in the copolymers of either chiral bulky 1 and achiral nonbulky 3, or chiral nonbulky 2 and achiral bulky 7. The smaller the pendant group in the copolymerization of achiral monomers with 1, the more easily did the preferential helical sense change with the copolymer composition. However, the copolymers of chiral nonbulky 2 and achiral nonbulky 3 did not change the helical sense, irrespective of the composition. The free energy differences between the plus and minus helical states, as well as the excess free energy of the helix reversal, of those chiral-achiral random copolymers were estimated by applying a modified Ising model.
N-炔丙基苯甲酰胺1-7与(nbd)Rh(+)[η(6)-C(6)H(5)B(-)(C(6)H(5))(3)]聚合，以高收率得到中等分子量（M(n)=26,000-51,000）的聚合物。(1)H NMR光谱表明，这些聚合物具有相当规整的结构（顺式含量为81-88%）。光学活性聚合物聚(1)和聚(2)，通过其强烈的CD信号和大的旋光度证明，在CHCl(3)或甲苯中加热时，它们采用稳定的螺旋构象，且单手螺旋方向过量。通过改变手性大体积单体1与非手性小体积单体3，或手性小体积单体2与非手性大体积单体7在共聚物中的含量，可以控制Cotton效应的符号。在非手性单体与1的共聚中，侧基越小，优先螺旋方向随共聚物组成变化越容易。然而，手性小体积单体2与非手性小体积单体3的共聚物，无论组成如何，都不会改变螺旋方向。通过应用修正的Ising模型，估算了那些手性-非手性无规共聚物的正、负螺旋态之间的自由能差，以及螺旋反转的过量自由能。
