We report the synthesis of block copolymers of monomethoxylated polyethylene glycol and poly(glycerol carbonate) (mPEG-b-PGC) via the ring-opening polymerization of benzyl glycidyl ether, monomethoxylated polyethylene glycol, and carbon dioxide using a cobalt salen catalyst. The resulting block copolymers display high polymer/cyclic carbonate selectivity (>99%) and, if two oxirane monomers are used, random incorporation into the polymer feed. The resulting diblock mPEG-b-PGC polymer shows promise as a nanocarrier for surfactant-free, sustained chemotherapeutic delivery. mPEG-b-PGC, with paclitaxel conjugated to the pendant primary alcohol of the glycerol polymer backbone, readily forms 175 nm diameter particles in solution and contains 4.6 wt % paclitaxel (PTX), which is released over 42 days. The mPEG-b-PGC polymer itself is noncytotoxic, whereas the PTX-loaded nanoparticles are cytotoxic to lung, breast, and ovarian cancer cell lines.