One-Pot, One-Step to Access Cyclic Amphiphilic Block Copoly(carbonate-b-ester)

Abstract

Amphiphilic block copolymers containing a cyclic topology exhibit distinct physical properties that can be exploited to obtain fascinating nanostructures for various applications. So far, these copolymers have been generally prepared via multistep approaches. Herein, we report the simultaneous zwitterionic copolymerization of δ-valerolactone (VL) and triethylene glycol carbonate (3EG) mediated by N-heterocyclic carbene to yield a cyclic amphiphilic block copoly­(ester-b-carbonate) in a one-pot, one-step strategy. The copolymerization temperature has a considerable impact on the block length (L VL and L 3EG); thus, a block copolymer (L VL = 12.7 and L 3EG = 10.1) is obtained at a low temperature (−25 °C), whereas a random copolymer is obtained at 50 °C with a high overall conversion (≥95%). The copolymerization proceeds with a 150 times faster consumption of VL compared to that of 3EG with reactivity ratios (r) r VL ≫ r 3EG (r VL ≈ 5, r 3EG ≈ 0.055), determined using the error-in-variables-model method, demonstrating the VL block chain during copolymerization. Moreover, a theoretical study indicates that the obtained copolymer is not a kinetically controlled product but rather a thermodynamically controlled product. Scanning and transmission electron microscopies revealed that the copoly­(ester-b-carbonate) self-assembled in a tetrahydrofuran/water solvent mixture (V THF/V H2O = 1:5) to form a cubic nanostructure.