Separation and quantification of dead species in styreneRAFT polymerization by gradient polymerelution chromatography

In living polymerization, the inevitable dead chain impurities, due to bimolecular termination and side reactions, are not only an obstacle for the synthesis of pure block copolymers but also an impairment in the application performance of the resulting polymer materials. In this paper, a simple separation and quantification method based on gradient polymer elution chromatography (GPEC) was developed to experimentally investigate the dead species in RAFT polymerization of styrene. The RAFT-prepared polystyrene (PSt) was extended with methyl acrylate in a specially-designed chain extension reaction, in which the living PSt chains were extended and transformed into block copolymer, but the remaining dead PSt chains (D-PSt) will remain constant and can be separated and quantified by GPEC. The systematic experimental investigation of the effect of various polymerization parameters on the mass fraction of dead species (fD-PSt) in RAFT-prepared polystyrene (PSt) was implemented. The results clearly demonstrated the initiator concentration and RAFT agent concentration can exhibit a linear and inversely proportional dependence on fD-PSt, respectively. In addition, the dead chains were found to be formed throughout the entire RAFT process. These unambiguous experimental data confirmed the previous theoretical calculation and model prediction, which may be beneficial to understand RAFT processes, optimize polymerization conditions and to minimize dead polymer contaminations. Moreover, the method based on GPEC proposed here was able to fractionate and quantify the dead and living species, which can serve as a powerful tool in the mechanistic study of the living radical polymerizations.