One-step synthesis of multi-alkyne functional hyperbranched polyglycerols by copolymerization of glycidyl propargyl ether and glycidol

Abstract

By copolymerization of glycidol with the alkyne-containing oxirane monomer glycidyl propargyl ether (GPE), hyperbranched polyglycerol (hbPG) with a defined number of alkyne functionalities (up to 38%) can be obtained in a one-step procedure. The number of alkynes can be adjusted by the glycidol/GPE ratio to provide multi-alkyne functional hbPGs, maintaining the highly branched polyether structure. Interestingly, the acidic proton of the alkyne moiety does not interfere with the proton exchange mechanism during the polymerization of glycidol. By specific modification of the synthesis procedure, crosslinking reactions can be suppressed. The polymers exhibit molecular weights ranging from 1800 to 5500 g mol⁻¹ (determined by ¹H NMR spectroscopy and SEC) with moderate polydispersities (M_w/M_n < 2.0, mostly <1.7). Using inverse gated ¹³C NMR spectroscopy and two-dimensional NMR techniques, the different repeat units of the copolymers can be assigned. The degree of branching value (DB) ranges from 0.58 to 0.50 for increasing GPE content, which is caused by an increased number of linear repeat units with increasing GPE content. The alkyne functionalities are readily available for derivatization reactions by copper-catalyzed azide–alkyne “click”-type cycloaddition reactions. The convenient synthesis and the broad applicability of the alkyne functionalities render these copolymers interesting building blocks for the preparation of complex polymer architectures by “click”-chemistry. This is exemplified by the attachment of hydrophobic azide end-functional polystyrene to yield amphiphilic branched copolymers containing exactly one hbPG block.