Molecular Weight Dependence of the Optical Rotation of Poly((R)-1-deuterio-n-hexyl isocyanate) in Dilute Solution

Abstract

Poly((R)-1-deuterio-n-hexyl isocyanate) (αPdHIC) in dilute solution is characterized by an extraordinarily large specific optical rotation [α]. Detailed [α] data were obtained for a number of nearly monodisperse αPdHIC samples in different solvents over a wide range of temperature. The results were similar to those for poly((R)-2-deuterio-n-hexyl isocyanate) (βPdHIC) reported in a previous publication (Gu, H., et al. Macromolecules 1995, 28, 1016). The molecular weight dependence of [α] was remarkable over a wide range and consistently analyzed by the statistical mechanical theory of Lifson et al. (Lifson, S., et al. J. Am. Chem. Soc. 1989, 111, 8850) for a polyisocyanate chain consisting of an alternating sequence of right-handed and left-handed helices intervened by helix reversals. It was shown that the large [α] arises from the helical conformation, where the left-handed helix exists in some excess over the right-handed one due to a small free energy favoring the former helix (2ΔG h). This energy accumulates to a significant amount on a given chain assisted by a very small helix reversal probability (ν). This confirmed a similar conclusion on βPdHIC reported in the previous paper. It was found that ν is almost the same for the two polyisocyanates but the magnitude of 2ΔG h for αPdHIC, though smaller than a few calories per mole, is about twice as large as that for βPdHIC, exhibiting a remarkable hydrogen−deuterium isotope effect on chain conformation.

Near-UV, circular dichroism, and fluorescence spectra of a rigid rodlike helical polysilane bearing trietheral moiety in ethanol/water

“…The kinks would be responsible for the formation of the chiral motifs. [10][11][12][13] Recently, several conformational kinks in 2's single molecule on sapphire are actually visualized by atomic force microscopy. 20 Such a conformational shrinkage associated with solvent polarity, also, is expected from the following FLA data.…”

“…To date, several optically active chromophoric helical polymers with -* and/or n-* transitions, induced by enantiomerically pure chiral or bulky achiral substituent, have been studied: polyacetylene, 1 polydiacetylene, 2 polythiophene, 3 polyisocyanide, [4][5][6] polyphenylenevinylene, 7 poly(quinoxaline-2,3-diyl), 8 polycarbodiimide, 9 polyisocyanate, [10][11][12][13] and poly(triphenylmethyl methacrylate).…”

“…Synthesis and spectroscopic characterization of a rigid rodlike polymer with a single-screw-helical sense that is stable in solution at room temperature have become of growing interest in recent years. To date, several optically active chromophoric helical polymers with -* and/or n-* transitions, induced by enantiomerically pure chiral or bulky achiral substituent, have been studied: polyacetylene, 1 polydiacetylene, 2 polythiophene, 3 polyisocyanide, 4-6 polyphenylenevinylene, 7 poly(quinoxaline-2,3-diyl), 8 polycarbodiimide, 9 polyisocyanate, [10][11][12][13] and poly(triphenylmethyl methacrylate). 14 These conformational structures have been analyzed by nuclear magnetic resonance (NMR), circular dichroism (CD), ultraviolet (UV)-vis, fluorescence (FL), circularly polarized luminescence spectroscopies, optical rotation, or gel permeation chromatography equipped with a light scattering detector; in some cases, by a couple of these methods.…”

Chain architecture and flexibility of α-cyclodextrin/PEG polyrotaxanes in dilute solutions

“…After dividing L with the diameter d, the axial ratio (R a ) was obtained and listed in the 7th column in Table 2. When we compare this value with typical semiflexible chains such as schizophyllan (153), 14,15 poly(n-hexyl isocyanate) (46), 16 sodium hyaluronate (8.2) 17 and a polystyrene polymacromonomer (3-4), 9 the present system has a similar flexibility to those of polystyrene polymacromonomer and cylindrical lipid micelles. 18 During our iteration process to fit the data, we had to choose a shorter L than that of the PEG chain template.…”

Polysilane Organogel with Hierarchical Structures Formed by Weak Intra-/Inter-chain Si/FC and van der Waals Interactions

“…It was also already established that two polyisocyanates bearing alkyl side chains with a chiral H/D isotope effect in hexane at 25 C are able to adopt a semiflexible helical conformation with almost one-screw-sense, with a cooperative amplification mechanism of inter-side-chains by the product of the repeating numbers of $2000 and an ultraweak chiral bias of 0.4-0.7 cal per repeat unit. 15 If such ultraweak Si/FC intrachain interactions are applicable to the Si/FC interchain interactions of polymers in organic solvents, then the interchain interactions may effectively act as noncovalent crosslinks to create an efficient polymeric organogelator. Because PSi5 has three fluorine atoms in the side group, one fluorine and the remaining two fluorines may contribute to Si/FC intrachain and interchain interactions, respectively (see, Figure 15 in ref 12).…”