RAFT polymerization of methyl 6-O-Methacryloyl-α-D-glucoside in homogeneous aqueous medium.: A detailed kinetic study at the low molecular weight limit of the process

We report a detailed kinetic study of the RAFT polymerization of methyl 6-O-methacryloyl-alpha-D-glucoside (a methacrylic ester-type glycomonomer) with the chain transfer agent (CTA) (4-cyanopentanoic acid)-4-dithiobenzoate and initiator 4,4'-azobis(4-cyanopentanoic acid) in homogeneous aqueous media. The influence of temperature, initiator and CTA concentration, molar mass of the CTA radical leaving group, and the presence of residual oxygen on the polymerization kinetics were investigated in comparison with corresponding conventional free radical polymerizations (i.e., with no CTA present). RAFT processes were characterized by an initial non-steady-state period, the length of which depended inversely on the radical flux in the system, and were found to proceed at a significantly slower rate than the corresponding conventional free radical polymerizations. Also, attainment of the steady-state coincided with complete consumption of the initial CTA. The use of a macromolecular CTA reduced the length of the non-steady-state period but, interestingly, did not eliminate it, and the duration of this period was still shown to depend inversely on the initial CTA to initiator ratio. To our knowledge, this is the first time that a non-steady-state period has been observed in a RAFT polymerization initiated by a macromolecular CTA. Finally, the results of this investigation were used as a guide for the preparation of a series of well-defined living glyco-oligomers (DPn = 15-66, PDI = 1.05-1.12) in high yield.