“Click” Reactions: Novel Chemistries for Forming Well-defined Polyester Nanoparticles

We present the synthesis of discrete functionalized polyester nanoparticles in selected nanoscale size dimensions via a controlled intermolecular chain cross-linking process facilitated via “click”-chemistry approaches such as the Cu(I)-catalyzed 1,3-dipolar cycloaddition of azides and thiol−ene reactions. Both “click” reactions led to the formation of well-defined nanoparticles with narrow size distribution and selected nanoscopic size dimensions. The controlled coupling involves the cross-linking of an alkyne functionalized polyester with a bisazide, 1,8-diazide-3,6-dioxaoctane, and an allyl functionalized polyester with 3,6-dioxa-1,8-octanedithiol. The linear functional polyester precursors were synthesized via ring-opening copolymerization of δ-valerolactone and α-propargyl-δ-valerolactone as well as with α-ally-δ-valerolactone, respectively. We found that the nanoparticle formation and the control over the nanoscopic dimension are primarily influenced by the degree of the alkyne or allyl entity implemented in the precursor polymer and the amount of bisazide and dithiol cross-linking reagents. These results underline once more the versatility of the intermolecular chain cross-linking reaction which is not limited to epoxide chemistries but can be extended to “click” reactions to form controlled nanoparticles with comparable efficiencies. This work describes the utilization of alkyne−azide and thiol−ene “click” chemistries to facilitate the controlled assembly and cross-linking of supramolecular 3-D structures in selected nanoscopic ranges.