Preparation of hydrophobic helical poly(N-propargylamide)s in aqueous medium via a monomer/cyclodextrin inclusion complex

Abstract

We present a facile approach for the preparation of hydrophobic helical poly(N-propargylamide)s in aqueous medium instead of toxic and volatile organic solvent by using a monomer/cyclodextrin inclusion complex. Four hydrophobic substituted acetylene monomers were investigated in this study. Their inclusion complexes with hydroxypropyl-β-cyclodextrin (HP-β-CD) and hydroxypropyl-γ-cyclodextrin (HP-γ-CD) were prepared in water and identified with FT-IR and NMR spectroscopy. Polymerizations of the complexes were successfully carried out in aqueous solution in the presence of a water-soluble Rh-based catalyst [Rh(cod)₂BF₄; cod = 1,5-cyclooctadiene]. The as-prepared poly(N-propargylamide)s exhibited little difference in composition from the counterparts obtained in organic solvent according to FT-IR analysis. Circular dichroism and UV-Vis absorption spectra demonstrated that the as-prepared poly(N-propargylamide)s could take ordered helical conformations. The reusability of cyclodextrins in the polymerization was investigated quantitatively, which should be one of cyclodextrins' advantages but has never been highlighted before in literature. The versatile method for preparing hydrophobic helical poly(N-propargylamide)s can efficiently reduce the use of noxious organic solvents and can be applicable to the preparation of other helical polymers.