Heteroatom-containing degradable polymers by ring-opening metathesis polymerization

The incorporation of weak bonds containing heteroatoms along the polymer backbone has become a popular tool to accelerate degradation. Many methods have already been reported for the synthesis of degradable heteroatom-containing polymers based mainly on conventional step-growth and chain-growth ring-opening polymerizations (ROP). In recent years, ring-opening metathesis polymerization (ROMP) has evolved as an emerging approach for the synthesis of various types of degradable polymers, from carbocyclic norbornene derivatives to heterocyclic olefin monomers. The classic/high-performance ruthenium (Ru)-based catalysts are not only highly reactive to C=C double bonds but also highly tolerant to polar functional groups. Hence, a rich library of functional groups can be incorporated into cyclic olefin monomers and then transferred to the polymer backbone. This review covers the synthesis of various degradable heteroatom-containing (co)polymers via ROMP, including poly(thio)acetals/polyketals, polyorthoesters, polyesters, polycarbonates, polyphosphoesters/polyphosphoamidates, poly(enol ether)s, poly(silyl ether)s, polydisulfides, polyketones, polyacylsilanes, polyamides, and polyureas, as well as their degradable mechanism and ability under different conditions. The review also highlights applications in tissue engineering and medicine.