Synthesis and characterization of glycidyl azide polymers using isotactic and chiral poly(epichlorohydrin)s

Abstract

Isotactic and chiral glycidyl azide polymers (GAPs) have been synthesized by the reaction of isotactic and chiral poly(epichlorohydrin)s (PECHs) with sodium azide in dimethylformamide at 95 °C. The azidation does not affect the isotacticity of the chains, but the polymer backbone is degraded in the process; a GAP of high molecular weight (100 kg/mol) is nevertheless obtained. Despite the high isotacticity of the polymer chains, the GAPs are not crystalline. Long reaction times favor the branching and/or the cross-linking of the polymer. The isotactic and chiral PECHs used as starting materials for the GAP syntheses have been prepared by the Vandenberg process using racemic or chiral monomers, leading thus to partially ((RS)-PECH) or completely ((R)- or (S)-PECH) isotactic polymers, respectively. They have been split into a soluble and an insoluble fraction by acetone extraction. The fractionation of chiral PECH withdraws from the polymer the incompletely isotactic chains coming from the presence of monomers of opposite configuration in the chiral epichlorohydrin or from a defective polymerization process. The population of crystals remaining in the insoluble chiral PECH fraction is thus more homogeneous, leading to an improved crystallinity and a higher melting temperature.