Synthesis and properties of tunable thermoresponsive aliphatic polycarbonate copolymers with oligo ethylene glycol containing thioether and/or sulphone groups
A series of novel thermoresponsive copolycarbonates were constructed by cyclic trimethylene carbonate (MTC) monomers bearing oligo ethylene glycol (OEG) and with thioether or/and sulphone linkages. They were initiated by 1,4-benzenedimethanol with N-(3,5-trifluoromethyl)phenyl-N′-cyclohexylthiourea (TU)/1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) as the organic catalyst. The lower critical solution temperature (LCST) properties of the polycarbonates with thioether or sulphone linkage were studied and discussed with regard to molecular weight, salt concentration and polymer concentration. By using monomers of different OEG chain lengths and thioether and/or sulphone linkages, the LCSTs of biodegradable and thermoresponsive polycarbonate copolymers can be easily tuned within a wide temperature window from 0 °C to 46 °C (3 g L−1 in aqueous solution). In addition, block polycarbonates with two tunable LCSTs were further synthesized and investigated. Results showed that LCST1 was constructed by polycarbonate with a hydrophobic thioether linkage, while the LCST2 was achieved by a polycarbonate containing hydrophilic sulphone linkage.