ROMP synthesis of benzaldehyde-containing amphiphilic block polynorbornenes used to conjugate drugs for pH-responsive release

The development of novel polymer carriers, which have well-defined structures and desired conjugative abiltiy to therapeutic agents, is still an urgent requirement in the field of polymer–drug conjugates (PDCs) used for stimuli-responsive drug delivery systems. Herein, we present the controlled synthesis of a novel amphiphilic polynorbornene-based block copolymer, side-chain containing hydrophobic functionalizable benzaldehyde groups and hydrophilic dentritic triethylene glycol (TEG) moieties, by the ring-opening metathesis polymerization (ROMP) using the 3rd generation Grubbs catalyst 1 as the initiator. The obtained copolymer can self-assemble into spherical micelles with the average size of 84 nm in water, and its remarkable ability as the polymer carrier to fabricate PDCs was fully confirmed by the efficient covalently Schiff-base linking of its side-chain benzaldehyde groups to amino groups of model drugs including O-benzylhydroxylamine (BHA), 1-hexadecanamine, tryptophan and benzocaine. Notably, torispherical micelles with the average size of 90 nm were also obtained by the self-assembly of the formed polymer-BHA conjugate, and the pH-triggered release of BHA molecules from the micelles was observed at acidic environments (for example, pH 4.0 and 2.5). Therefore, the present polynorbornene block copolymer is expected to find potential applications in the stimuli-responsive drug delivery systems as a promising polymer carrier to form PDCs via acid-responsive Schiff-base linkage with amino-containing drugs such as doxorubicin, daunorubicin, epirubicin and pirarubicin.