Synthesis of a Star Polymer Library with a Diverse Range of Highly Functionalized Macromolecular Architectures

Abstract

An efficient and versatile synthetic route toward highly functionalized core cross-linked star (CCS) polymers with interesting structures and properties is presented using an alkyne CCS polymer as scaffold. The alkyne CCS polymer scaffold was initially prepared via an improved arm-first approach, through ring-opening polymerization (ROP) of 4,4′-bioxepanyl-7,7′-dione (BOD) with a poly(caprolactone-b-propargyl methacrylate) macroinitiator and stannous triflate (Sn(OTf)2) catalyst. Highly functionalized fluorescent, saccharide and amphiphilic CCS polymers were synthesized by grafting the alkyne CCS polymer with the corresponding azido substituted compounds via copper catalyzed 1,3-dipolar azide−alkyne cycloaddition (CuAAC), ‘click’ chemistry. The resulting corona-functionalized CCS polymers were characterized via GPC, 1H NMR spectroscopic analysis and DLS. 1H NMR spectroscopic analysis revealed that the grafting efficiency (i.e., click efficiency) ranged from 10 to >99% and was highly dependent on the structure and functionality of the azido compounds. This equates to the grafting of 45 to 450 functional compounds onto the CCS polymer scaffolds corona. The results indicate that the click functionalization efficiency is closely related to the molecular size of the azido compounds. Other than size, factors including molecular structure, compatibility and synergistic driving forces, such as the formation of potential inclusion complexes, are also found to affect the functionalization efficiencies.