Efficient Metal-Free “Grafting Onto” Method for Bottlebrush Polymers by Combining RAFT and Triazolinedione–Diene Click Reaction

An efficient metal-free "grafting onto" method was developed for preparing bottlebrush polymers based on the combination of reversible addition fragmentation chain transfer polymerization (RAFT) and triazolinedione (TAD) diene Diels-Alder cycloaddition reaction. In this approach, RAFT and a following postfunctionalization process were used to prepare the polyacrylate backbone with conjugated diene side group in each repeat unit (PHEA diene) and the various TAD-terminated polymer sides including poly(methyl methacrylate) (PMMA), poly(tert-butyl acrylate) (PtBA), and polystyrene (PS). The TAD diene Diels-Alder cycloaddition reaction was then employed to efficiently couple the resultant polymer backbone and side chains, which produced the corresponding bottlebrush polymers of PHEA(448)-g-PMMA(27), PHEA(448)-g-PtBA(25), and PHEA(448)-g-PS25 with a high grafting density above 90% in only 1 min in the presence of slight molar excess (1.2 times) of TAD to diene groups. The quantitative grafting density could be further achieved in less than 10 min coupling reaction. Atomic force microscopy (AFM) characterization visualized the worm-like molecular morphology for all cases.