Polylactones. 16. Cationic Polymerization of Trimethylene Carbonate and Other Cyclic Carbonates

1,3-Dioxanone-2 (trimethylene carbonate) was polymerized by use of methyl triflate or triethyloxonium fluoborate under various reaction conditions. Chloroform, 1,2-dichloroethane, and nitrobenzene were used as solvents; the temperature was varied between 25 and 50°C; and the monomer/initiator ratio between 50 and 400. However, inherent viscosities above 0.29 dL/g ( M n > 6000) were never obtained, owing to side reactions such as backbiting and formation of ether groups. IR and 1H-NMR spectroscopy revealed that the polymerization mechanism agrees with that of the cationic polymerization of lactones in that propagation involves cleavage of the alkyl-oxygen bond. The active cationic chain end and the dead methylcarbonate end groups were identified by means of 1H-NMR spectra. A reaction mechanism for the formation of ether groups is discussed. Furthermore, 1H-NMR spectroscopy indicated that ethylene carbonate and biphenyl-2,2′-carbonate do not react with methyl triflate at 20, 60, or even 100°C.