Concurrent Cationic Vinyl-Addition and Coordination Ring-Opening Copolymerization via Orthogonal Propagation and Transient Merging at the Propagating Chain End

Abstract

Controlled cationic vinyl-addition polymerization of an alkyl vinyl ether (VE) and ring-opening polymerization of ε-caprolactone (CL) simultaneously proceeded using HfCl4/Hf­(OBu)4 as a dual-role catalyst for both mechanisms, yielding a graft copolymer consisting of a poly­(VE) main chain and several poly­(CL) side chains. The copolymer of conventionally incompatible monomers was generated via the unprecedented mechanisms consisting of orthogonal propagating reactions and transient merging. Specifically, the poly­(CL) chains were incorporated into a poly­(VE) chain through an exchange reaction between the VE-derived alkoxy group and the propagating poly­(CL) chain at the acetal moiety of the propagating end of the poly­(VE) chain. An appropriate ratio of HfCl4 and Hf­(OBu)4 was indispensable for both the simultaneous vinyl-addition and ring-opening polymerizations and the alkoxy group exchange reaction.

Tandem Unzipping and Scrambling Reactions for the Synthesis of Alternating Copolymers by the Cationic Ring-Opening Copolymerization of a Cyclic Acetal and a Cyclic Ester

“…Simultaneous copolymerization via different mechanisms is an intriguing strategy for synthesizing highly functional polymer materials. − In particular, copolymers with different types of monomers can be obtained without cumbersome multistep reactions involving purification and isolation. For example, a diblock copolymer of ε-caprolactone (CL) and styrene was produced in one pot via simultaneous (but orthogonal) living coordination ring-opening polymerization (ROP) and nitroxide-mediated radical polymerization using a bifunctional initiator with initiating sites for both polymerizations .…”

“…This class of copolymerization includes the copolymerization of vinyl monomers and cyclic monomers via the concurrently occurring vinyl-addition and ring-opening mechanisms − and chain- and step-growth copolymerization. , These polymerizations are effective for the synthesis of multiblock-type copolymers via two-way crossover reactions. A wider variety of copolymer sequences and architectures can be produced via this type of copolymerization by completely different intermediates or mechanisms, , because the relative rates of both reactions are tuned independently by changing the reaction conditions, such as the amount of catalyst and the solvent polarity.…”

Recent advances in applications of vinyl ether monomers for precise synthesis of custom-tailored polymers

“…During the reaction, the non-homopolymerizable ketone monomer reacted with the oxetane-derived oxonium ion giving rise to carbocation capable of reacting with VE only (Scheme 31). Vinyl-addition polymerization of VE and simultaneous ring-opening polymerization of εcaprolactone under hafnium-mediated control afforded graft copolymers [189,190]. An approach based on successive living cationic polymerization of MOVE, EOVE or EOEOVE, followed by ring-opening polymerization of L-lactide, enabled precision synthesis of block copolymers exhibiting well-defined organization of poly(VE) and poly(lactide) blocks [191].…”

Hydroboration of Aldehydes, Ketones, and Carbodiimides Promoted by Mono(imidazolin‐2‐iminato) Hafnium Complexes

“…Complexes of hafnium have been predominantly used as Lewis acid catalysts in various organic transformations, such as the polymerization of cyclic esters, and as catalysts for the homo‐ and copolymerization of α‐olefins . Recently, Hf‐MOF compounds have been used as active catalysts for the activation of small molecules .…”