Hydrogen-Deuterium Isotope Effects and Chiral Solvation in Polymer Solutions

1.氢取代旋光活性聚异氰酸酯S在稀溶液中的螺旋构象测定了在稀溶液中正己基侧链的α或β碳上有氢取代的聚异氰酸酯S的旋光度随分子量和温度的变化。结果用Lifson等人的S统计热力学理论进行了拟合，其中假设多异氰酸酯链上的每个单体都呈现三种状态之一，即左旋螺旋、右旋螺旋和螺旋反转。通过拟合，每个单体的左右螺旋之间的自由能差DELTAG_h估计为几卡/摩尔，而螺旋反转的自由能超过3000卡/摩尔。前者的值表明氢-氚同位素对单体构象的影响很小。然而，后者的值表明了螺旋反转发生的难度。这一困难积累了小DELTAG_…2.多异氰酸酯在液晶溶液中的螺旋构象光学不活泼的聚异氰酸酯以外消旋混合物的形式存在，其浓溶液形成向列相。将一些光学活性低摩尔质量的物质或由一些光学活性和非活性异氰酸酯单体组成的共聚物加入到向列型溶液中，溶液由向列型转变为胆甾型。这一转变表明，由于与光学活性物质的手性相互作用的积累，导致了PHY链中左右螺旋状态的不成比例。尽管上述共聚物在稀溶液中的旋光取决于单体组成，但诱导胆甾相结构的节距并不取决于单体组成。这种独立性可以通过在液晶溶液中从共聚物链中排除螺旋反转态来解释。较少

1.Helical conformation of deuterium-substituted optically-active poly(hexyl isocyanate)s in dilute solutionThe optical rotation of poly(hexyl isocyanate)s with deuterium substituted on the alpha- or beta-carbon in the hexyl side chain was measured in dilute solution as a function of the molecular weight and temperature. The results were fitted by Lifson et al.'s statistical thermodynamic theory, where each monomer in the polyisocyanate chain was assumed to take one of three states, the left-handed helix, right-handed helix, and helix reversal. From the fitting, the free energy difference DELTAG_h between left- and right-handed helices per monomer was estimated to be a few cal/mol, while the free energy of the helix reversal more than 3000 cal/mol. The former value indicates a very small hydrogen-deuterium isotope effect on the monomer conformation. However the latter value demonstrates the difficulty in the occurrence of the helix reversal. This difficulty accumulates the small DELTAG_ … More h to provide a large disproportion of the left- and right-handed helical monomers in the chain.2.Helical conformation of polyisocyanates in liquid crystalline solutionOptically inactive poly(n-hexyl isocyanate)(PHIC) exists as a racemic mixture, and it's concentrated solution forms a nematic phase. When some optically active low-molar-mass substances or copolymers consisting of some optically active and inactive isocyanate monomers were added to the nematic solution of PHIC, the solution transformed from the nematic to cholesteric. This transformation indicates the disproportion of the left- and right-handed helical states in the PHIC chain due to an accumulated chiral interaction with the optically active substances.Although the optical rotation of the above copolymer in dilute solution depended on the monomer composition, the pitch of the induced cholesteric structure did not. This independence can be explained by the exclusion of the helix reversal state from the copolymer chain in the liquid crystalline solution. Less