Precise synthesis of thermoreversible block copolymers containing reactive furfuryl groups via living anionic polymerization: the countercation effect on block copolymerization behavior

The anionic block copolymerization of 4,4′-vinylphenyl-N,N-bis(4-tert-butylphenyl)benzenamine (A) with furfuryl isocyanate (B) was carried out using potassium naphthalenide (K-Naph) in tetrahydrofuran at −78 and −98 °C to prepare well-defined block copolymers containing furan groups for the formation of thermoreversible networks via a Diels–Alder (DA) reaction. While no block copolymerization was observed in the absence of sodium tetraphenylborate (NaBPh₄) due to side reactions, well-defined poly(B-b-A-b-B) (PBAB) copolymers with controlled molecular weights (M_n = 18 700–19 500 g mol⁻¹) and narrow molecular weight distributions (M_w/M_n = 1.08–1.17) were successfully synthesized in the presence of excess NaBPh₄. The occurrence of the undesirable side reactions during polymerization of B was effectively prevented by NaBPh₄, which results in the change in the countercation from K⁺ to Na⁺ for further polymerization of B. The cross-linking via the DA reaction between the furan groups of PBAB and bismaleimide was proved by FT-IR and differential scanning calorimetry (DSC), and the thermoreversible properties of the cross-linked polymer were subsequently investigated using DSC and solubility testing.