Precision AABB-type cyclocopolymers via alternating cyclocopolymerization of disiloxane-tethered divinyl monomers

Abstract

Attempts to synthesize copolymers with structural sophistication and precision still remain elusive. Here, we report a facile synthesis of a new type of precision cyclocopolymer containing an AABB-type repeating chain sequence via the free radical cyclopolymerization of divinyl monomers bMA and bSt in the presence of ZnCl₂. RAFT polymerization conditions can afford the AABB-type alternating cyclocopolymers with controlled molecular weight and narrow polydispersity. Kinetic research on the cyclocopolymerization shows that bMA and bSt polymerize in an equimolar ratio during the ZnCl₂-modulated RAFT copolymerization process. The AABB-type alternating structures are verified by 2D ¹H–¹³C COSY techniques and MALDI-TOF MS. The main-chain CH or CH₂ NMR signals (both ¹H and ¹³C NMR) in the cyclocopolymers suggest a chain sequence of a high order, and prove the absence of either the homopolymer structures or the intersecting ABAB-type structure. MALDI-TOF MS shows that the cyclocopolymer has a regularly repeating structure and a uniform repeating unit. In the absence of ZnCl₂, bMA prefers to homopolymerize. Our work shows that the alternating cyclocopolymerization is a facile route to afford cyclocopolymers with a precision chain sequence and group spacing.