Abstract
Three types of ethylene oxide-based and carbonate-containing copolymers were prepared through copolymerization of ethylene oxide (EO) with CO2 under metal-free conditions in the presence of triethylborane (TEB), using onium salts (OS) as initiator. Hydrophobic poly[(ethylene carbonate)(x)-co-(ethylene oxide)(y)] (PECEO) samples with carbonate contents above 90% (x >> y) were first prepared under a CO2 pressure of 10-30 bar with a ratio of [TEB] to [OS] of 1-1.2 equiv in tetrahydrofuran (THF) or in hexane. The above PECEO (carbonate > 91%) then served as a macroinitiator to grow two external poly(ethylene oxide) (PEO) blocks and generate in one-pot amphiphilic PEO-b-PECEO-b-PEO triblocks. Lastly, the copolymerization of EO under a low pressure of CO2 (1-2 bar) with a ratio of [TEB] to [OS] of 1.2-2.0 equiv afforded hydrophilic poly[(ethylene oxide)(y)-co-(ethylene carbonate)(x)] (PEOEC) random copolymers with carbonate contents below 10% (y >> x); allyl glycidyl ether (AGE) was also terpolymerized with EO and CO2 under the same conditions to introduce functional groups along the backbone of PEO chains. Critical micelle concentrations (CMC) and size of micelles were measured for amphiphilic PEO-b-PECEO-b-PEO samples and compared with the values of other nonionic surfactants. The properties of "PEO-like" hydrophilic PEOECs were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and wettability test; their degradation behavior was further investigated under different conditions.