One-shot controlled/living copolymerization for various comonomer sequence distributions via dual radical and cationic active species from RAFT terminals

Abstract

In this study, we investigated one-shot copolymerization of vinyl ether with acrylates or vinyl esters in the presence of an aluminum-based Lewis acid and azo-initiator in toluene at 20 °C. In this system, isobutoxyethyl ethyl trithiocarbonate (BEETC) was employed as a RAFT reagent to control the molecular weight of the produced copolymers. In the presence of a weak and bulky Lewis acid, i.e., ethylaluminium bis(2,6-di-tert-butylphenoxide) [EtAl(ODBP)₂], the alternating radical RAFT copolymerization of IBVE and acrylates proceeded without the cationic homopolymerization of IBVE. Conversely, using a strong Lewis acid such as ethylaluminum dichloride (EtAlCl₂), interconvertible controlled/living copolymerization via dual radical and cationic species was induced and generated various comonomer sequence distributions, such as partitioned multiblock and tapered block copolymers, by kinetic resolution of the two monomers depending on the loading concentration of the Lewis acid. In both cases, the number-average molecular weights of the copolymers increased with the monomer conversions even in the presence of the Lewis acid, and they agreed well with the calculated values by assuming that all chains were formed from the BEETC molecule. The dual cationic and radical copolymerization process was also amenable to the combination of IBVE and vinyl acetate, when coupled with xanthate as the RAFT agent and ZnCl₂ as the Lewis acid catalyst for cationic polymerization.