Two is better than one: Repetitive ABA sequences in copolymers were obtained by a palladium‐templated monomer. Crucial in the polymerization were π–π‐stacking interactions between aromatic side groups to array three vinyl groups (see picture). Because of the interactions double cyclopolymerization at the palladium‐templated monomer was possible. Removal of the template led to sequence‐regulated copolymers.
For alternating repeat-unit sequence via living radical polymerization, ''template monomers'' were designed and polymerized, where two polymerizable alkene (vinyl) functions [e.g., methacrylate (M) and acrylate (A)] were placed side by side at the 1,8-positions on a rigid naphthalene scaffold. Even for such a divinyl monomer, highly selective intramolecular radical propagation was achieved with metalcatalyzed living radical polymerization systems, to give linear controlled polymers without crosslinking. The naphthalene template was cleaved via hydrolysis from the resultant polymer, and subsequently methylated for sequence characterization. 1 H NMR analysis demonstrated that the polymers consisted of highly alternating sequences (A-M-A: >80%), practically free from homo triad sequences (M-M-M).Scheme 1 Template systems towards sequence controlled radical polymerization with a template initiator (A) and a template monomer (B: this work).
There is a growing interest in sequence-controlled polymers toward advanced functional materials. However, control of side-chain order for vinyl polymers has been lacking feasibility in the field of polymer synthesis because of the inherent feature of chain-growth propagation. Here we show a general and versatile strategy to control sequence in vinyl polymers through iterative radical cyclization with orthogonally cleavable and renewable bonds. The proposed methodology employs a repetitive and iterative intramolecular cyclization via a radical intermediate in a one-time template with a radical-generating site at one end and an alkene end at the other, each of which is connected to a linker via independently cleavable and renewable bonds. The unique design specifically allowed control of radical addition reaction although inherent chain-growth intermediate (radical species) was used, as well as the iterative cycle and functionalization for resultant side chains, to lead to sequence-controlled vinyl polymers (or oligomers).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.