Water-Soluble Chiral Polyisocyanides Showing Thermoresponsive Behavior

Abstract

To afford chiral polyisocyanides with thermoresponsiveness may open new gates to enhance their functionality and to broaden their applications. Herein, we report the synthesis of a series of novel polyisocyanides carrying oligoethylene glycols (OEGs) modified dipeptides as the pendent groups. These polyisocyanides not only show different chiroptical properties but also possess characteristic thermoresponsive behavior. The corresponding monomers carrying different OEG units in the periphery are water-soluble, thus allowing their polymerization feasible in aqueous medium with NiCl 2 as the catalyst. For comparison, polyisocyanides were also prepared in organic solvents, such as dichloromethane and tetrahydrofuran. The effects of solvent and polymerization temperature as well as chemical structures of the pendants on the chiroptical properties of the resulting polymers were examined. The characteristic thermoresponsive behavior of these chiral polymers was investigated by 1 H NMR spectroscopy and turbidity measurements using UV/vis spectroscopy. The thermally induced aggregation processes were also followed by dynamic light scattering. It was found that the phase transition temperatures of these polymers were significantly influenced not only by the overall hydrophilicity but also by their secondary structures.

Synthesis of polymers with densely-grafted oligo(ethylene glycol)s by Pd-initiated polymerization of oxyethylene-containing diazoacetates

“…[6][7][8][9][10][11][12] Fig. As a result, it was found that the polymers bearing a short OEG side chain (x = 1-3) show an LCST-type phase separation in an aqueous medium, as is the case with other OEG-containing polymers.…”

“…Up to now, various types of polymer backbones have been utilized to realize temperature-responsive OEG-based polymers, such as poly(vinyl ethers), 6 polyacrylates, 7 polymethacrylates, 8 polystyrenes, 9 polycarbonates, 10 polyisocyanides, 11 and polyisocyanates. It is known that polymers carrying a short OEG side chain show a lower critical solution temperature-type (LCST-type) phase separation in water.…”

Thermal Properties of Methyl Ester-Containing Poly(2-oxazoline)s

“…One of the best-characterized thermoresponsive polymers is poly(N-isopropyl acrylamide) (PNIPAAm), which displays a lower critical solution temperature (LCST) of 32˝C, just below body temperature [2][3][4][5]. Other classes of thermoresponsive polymers that have emerged in recent years are for example poly(oligo ethylene glycol acrylate)s [2,6], polyisocyanopeptides grafted with oligo(ethylene glycol) side chains [7][8][9], poly(2-oxazine)s [10] and poly(2-oxazoline)s [3,5,[11][12][13][14][15][16][17].…”

Remarkable Structure Effects on Chiroptical Properties of Polyisocyanides Carrying Proline Pendants

“…The synthetic procedures for these monomers are outlined in Scheme 2, and their polymerization results are summarized in Table 1 (entries [8][9][10][11][12][13]. Motivated by these findings, we set out to examine the structural effects on the chiroptical properties of poly(phenyl isocyanide)s with these proline-based pendants.…”