Application of Thiourea/Halogen Bond Donor Cocatalysis in Metal-Free Cationic Polymerization of Isobutyl Vinyl Ether and Styrene Derivatives

Cationic polymerization of isobutyl vinyl ether (IBVE) was investigated using Schreiner's thiourea (STU) combined with Im-TEPB bearing a 2-iodoimidazolium cation and a noncoordinating borate anion. Both the CF3CO2H adduct and the HCl adduct of IBVE had the ability to initiate polymerization, but the number-averaged molecular weight was rather low compared with the theoretical value and the molecular weight distribution was fairly broad (M-w/M-n > 2.6). On the other hand, fast cationic polymerization of p-methoxystyrene (pMOS, 50 equiv relative to pMOS center dot HCl) proceeded using STU/Im-TEPB cocatalysts, giving rise to poly(pMOS) with M-n = 4580 and M-w/M-n = 1.38. STU/Im-TfO exhibited decreased activity due to the coordination of a trifluoromethanesulfonate counteranion with the NH group of STU, which was supported by the NMR spectrum, DFT calculation, and UV-vis titration experiment. The molecular weight of poly(pMOS) could be roughly regulated by STU/Im-TEPB cocatalysis between M-n = 2400 and M-n = 7500 by the monomer feed ratio with keeping the molecular weight distribution below 1.41, although these values were lower than the theoretical ones probably due to the unignorable chain-transfer reaction. The polymerization kinetics revealed that the monomer consumption rate depends on the concentration of Im-TEPB rather than STU, which reveals the catalytic function of STU/Im-TEPB.

Automated summary

This study investigated the cationic polymerization of isobutyl vinyl ether (IBVE) using Schreiner's thiourea (STU) combined with Im-TEPB. The polymerization of IBVE resulted in low number-averaged molecular weight and broad molecular weight distribution. On the other hand, fast cationic polymerization of p-methoxystyrene (pMOS) using STU/Im-TEPB yielded high molecular weight and narrow molecular weight distribution. The coordination of a trifluoromethanesulfonate counteranion with STU decreased the polymerization activity. The polymerization kinetics showed that the monomer consumption rate depended on the concentration of Im-TEPB.