Synthesis of a cyclic-brush polymer with a high grafting density using activated ester chemistry via the 'grafting onto' approach

In this work, novel cyclic-brush polymers with high grafting densities were successfully constructed via the grafting onto approach by combining a light-induced Diels–Alder ring-closure approach and activated ester chemistry as a post-modification method. The cyclic activated ester containing polymer precursor [poly(pentafluorophenyl 4-vinylbenzoate), c-PPF4VB4.0k] was synthesized by combining reversible addition–fragmentation chain transfer (RAFT) polymerization and the light-induced Diels–Alder click reaction, which was fully characterized by NMR, SEC, MALDI TOF mass and UV-Vis spectroscopy. Using activated ester chemistry, this cyclic polymer (c-PPF4VB4.0k), bearing a pentafluorophenyl group, was post-modified with PEG-NH2 to obtain a cyclic-brush polymer (c-PPF4VB4.0k-g-PEG) with hydrophilic grafting polymer chains and a hydrophobic cyclic polymer backbone. Meanwhile, c-PPF4VB4.0k was post-functionalized using propargyl amine to obtain a clickable cyclic polymer (c-P1). The cyclic polymer (c-P1) was further coupled with an azide-containing polymeric chain (l-PS-N3) to produce the cyclic-brush polymer (c-P1-g-PS). This work illustrated a concept for constructing cyclic-brush polymers by combining the ring-closure strategy and activated ester chemistry. Notably, these two cyclic-brush polymers exhibited high grafting densities (almost quantitatively) and narrow molecular weight distribution (Mw/Mn < 1.10).