Organocatalytic sequential ring-opening polymerization of cyclic ester/epoxide and N-sulfonyl aziridine: metal-free and easy access to block copolymers

Abstract

We report an organocatalytic sequential ring-opening polymerization (ROP) approach for the facile synthesis of polysulfonamide-based copolymers. Alcohols and methoxylpolyethylene glycols were initially employed as (macro)initiators for the ROP of N-sulfonyl aziridines to produce well-controlled polymers with the assistance of tosyl isocyanate. Tosyl isocyanate efficiently transformed the hydroxyl species into the tosylcarbamate anion, the initiating site for the ROP of N-sulfonyl aziridines. ROP of ε-caprolactone or propylene oxide was then performed in bulk in the presence of the phosphazene base t-Bu-P₂ or t-Bu-P₄, followed by end-group transformation with tosyl isocyanate and the subsequent ROP of N-sulfonyl aziridines. The synthesized poly(ε-caprolactone)-block-polysulfonamide and poly(propylene oxide)-block-polysulfonamide copolymers showed a remarkable control of molar masses and dispersities. Well-defined triblock and 3-arm star-shaped copolymers were successfully prepared from diol and triol initiators.