Effect of Side Chain Structure on the Conformation of Poly(N-propargylalkylamide)

Abstract

HCtCCH2NHR) having various alkyl groups (R ) CH3, C2H5, C3H7, i-C3H7, i-C4H9, n-C5H11, n-C7H15) were homopolymerized or copolymerized with a chiral comonomer, (R)-N-propargyl-3,7-dimethyloctanamide (2), in the presence of a Rh initiator to establish the relationship between the main-chain conformation and the structure of the pedant groups. 1 H NMR and viscosity measurements of the homopolymers revealed that the structure of the pendant groups markedly influences the rigidity of the polymer backbone and the stability of the helical conformation. The copolymerization using the achiral comonomers having linear or R-branched alkyl groups showed poor or no cooperative effects on the helical conformation, meaning that these polymers exist in a disordered state. On the other hand, a stable helical conformation, i.e., a long persistence length of the helical domain, was attainable for the polymer having -branched alkyl chains (poly(1e), R ) i-C4H9), which was evidenced by a clear, positive nonlinear relationship between the feed ratio of 1e to 2 and the optical rotation of the copolymers. UV-visible spectroscopic studies demonstrated that, in CHCl3, the helical and disordered main chains display absorption centered at 400 and 320 nm, respectively, which resulted in different colors in solution of the helical (yellow) and disordered (achromic) polymers. Thermochromism was achieved by the thermally induced reversible conformational change between helical and disordered states. The thermodynamic parameters (∆G r, ∆Hr, and ∆Sr) that govern the stability of the helical conformation of a copolymer were estimated by the temperature dependence of the populations of the helical and disordered states using UV-visible spectra.

Amplification of macromolecular helicity of dynamic helical poly(phenylacetylene)s bearing non-racemic alanine pendants in dilute solution, liquid crystal and two-dimensional crystal

“…34,35 Generally, if helical copolymers consisting of non-racemic monomers show a detectable change in their absorption and CD spectra, depending on the ee values of the monomer units, resulting from a conformational change, it is difficult to determine their handedness and to quantify their helix-sense excesses, based on the Cotton effect intensity of the corresponding optically pure homopolymer. In the present study, we assume that the copolymers, poly(1L m -co-1D n ), may have a helical conformation different from that of the poly-IL in benzene at low temperatures, but with a negligibly small helix-sense excess, thus showing weak ICDs.…”

Synthesis and characterization of optically active poly(phenylene-ethynylene)s containing chiral oxazoline derivatives

“…Moreover, peaks assignable to the oxazoline groups in the polymer were present; these peaks were not present in the spectrum of the corresponding monomer. In addition, the presence of a carbon-carbon triple bond in the polymer was confirmed by 13 C NMR, and the peaks for the triple-bonded carbons were observed at d values around 89.2 and 90.9 p.p.m., as depicted in Figure 2.…”

“…The structures of the polymers were confirmed by 1 H NMR, 13 C NMR and infrared spectroscopy. The 1 H NMR spectrum of the polymer in CDCl 3 is given in Figure 1.…”

“…5 Synthetic helical polymers are used in a variety of applications, including the separation of racemic compounds, the production of chemical and biological sensors and the catalysis of asymmetric syntheses. [6][7][8][9] In recent years, a variety of synthetic helical polymers have been synthesized, including poly(acetylene)s, 10 poly(m-phenylene)s, 11 poly(isocyanide)s 12 and poly(N-propargylalkylamide)s. 13 These polymers stabilize their conformations by steric repulsion and intramolecular hydrogen bonding among side-chain groups. In particular, poly(phenylene-ethynylene)s (PPEs) have attracted attention because of their easy synthesis via the Sonogashira-Hagihara coupling reaction.…”

Chiroptical study and conformation analysis of helical polymers surrounded by helical hydrogen-bonding strands

“…This biomimetic way of helix formation may develop a new methodology of designing synthetic helical polymers. We have incorporated a wide variety of pendent groups into poly(N-propargylamides) including linear and branched alkyl groups [9], aryl groups [10], hydroxyl groups [11], carboxyl groups [12], cyclics [13], esters [14], photo-responsive [15] and photoluminescent groups [16] to find that the stability and sense of the helical structure are tunable with external stimuli such as polar solvents, pH, heat and light. In the course of our study on a series of poly(N-propargylamides), we have examined the chiroptical properties of poly(N-(3-butynyl)amide), an analog of poly(N-propargylamide), to find it exhibits a completely different CD spectroscopic pattern from that of poly(N-propargylamide) [17].…”