Template-Directed Synthesis of Structurally Defined Branched Polymers

A grand challenge in materials chemistry is the synthesis of macromolecules and polymers with precise shapes and architectures. In this work, we describe a hybrid synthetic strategy to produce structurally defined branched polymer architectures based on chemically modified DNA. Overall, this approach enables precise control over branch placement, grafting density, and chemical identity of side branches. We utilize a two-step scheme based on polymerase chain reaction (PCR) for site-specific incorporation of non-natural nucleotides along the main polymer backbone, followed by copper-free “click” chemistry for grafting side branches at specific locations. In this way, linear DNA backbones are first synthesized via PCR by utilizing the promiscuity of a high yield thermophilic DNA polymerase to incorporate nucleotides containing bioorthogonal dibenzocyclooctyne (DBCO) functional groups at precise locations along one strand of the DNA backbone. Following PCR, copper-free “click” chemistry is used to attach synthetic polymer branches or oligonucleotide branches to the DNA backbone, thereby allowing for the synthesis of a variety of precise polymer architectures, including three-arm stars, H-polymers, and graft block copolymers. Branched polymer architectures are characterized using polyacrylamide gel electrophoresis, denaturing high performance liquid chromatography (HPLC), and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. In a proof-of-principle demonstration, we synthesize miktoarm stars with AB2 structures via attachment of mPEG-azide branches (1 and 10 kDa) at precise locations along a DNA backbone, thereby expanding the chemical functionality of structurally defined DNA topologies.