A novel type of optically active helical polymers: Synthesis and characterization of poly(N‐propargylureas)

Abstract

This article presents two novel artificial helical polymers, substituted polyacetylenes with urea groups in side chains. Poly(4) and poly(5) can be obtained in high yields (≥97%) and with moderate molecular weights (11,000–14,000). Poly(4) contains chiral centers in side chains, and poly(5) is an achiral polymer. Both of the two polymers adopted helical structures under certain conditions. More interestingly, poly(4) exhibited large specific optical rotations, resulting from the predominant one‐handed screw sense. The helical conformation in poly(5) was stable against heat, while poly(4) underwent conformational transition from helix to random coil upon increasing temperature from 0 to 55 °C. Solvents had considerable influence on the stability of the helical conformation in poly(4). The screw sense adopted by the helices was also largely affected by the nature of the solvent. Poly(4‐co‐5)s formed helical conformation and showed large optical rotations, following the Sergeants and Soldiers rule. By comparing the present two polymers (with one NH groups) with the three polymers previously reported (with two NH groups in side chains), the nature of the hydrogen bonds formed between the neighboring urea groups played big roles in the formation of stable helical conformation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4112–4121, 2008

A Novel Type of Mono-Substituted Polyacetylene: Synthesis and Characterization of Poly(N-Propargylthiourea)s

“…The lacking of ordered helical conformations in the currently studied poly(N -propargylthiourea)s is assumed to be originated in the two -N-H groups of poly(4) in the pendant chains. Both the two -N-H groups may participate in a three-dimensional hydrogen bonding with the sulfur in the neighboring C=S groups [35]. Similar situation was observed in earlier poly(N -propargylurea)s with similar molecular structures [26].…”

“…The results with respect to UV-Vis absorption spectra are similar to some mono-substituted polyacetylenes studied by us earlier, e.g., poly(N -propargylsulfamide)s [34] and poly(N -propargylurea)s [26]. However, under the investigated conditions, the present poly(N -propargylthiourea)s failed to form helical conformations, which were frequently observed in mono-substituted polyacetylenes [23][24][25]35]. The lacking of ordered helical conformations in the currently studied poly(N -propargylthiourea)s is assumed to be originated in the two -N-H groups of poly(4) in the pendant chains.…”

Optically Active Helical Substituted Polyacetylenes Showing Reversible Helix Inversion in Emulsion and Solution State

“…In addition, we examined the helix inversion behavior in only water-DMF mixture; however, we found even in the system with water-DMF = 0.5:9.5 (v/v), poly 1 (taken as example) remarkably the method reported by us earlier. [ 8 ] For poly 1 emulsion, the CD spectrum showed a CD signal with negative sign at ≈ 325 nm, while the corresponding polymer solution showed a CD signal with positive sign at ≈ 350 nm. Poly 2 gave similar effects with the exception of the sign of the CD signals.…”

Preparation of Optically Active Nanoparticles by Emulsification of Preformed Helical Polymers

“…We also designed and synthesized a series of helically substituted polyacetylenes. [9][10][11][12][13][14] In the course of our research, we found that a large part of the substituted polyacetylenes in particular with bulky pendent groups are poor in solubility. Some helical polyacetylenes loose the helical conformation under varied conditions, especially at elevated temperatures.…”