Mechanism of Spatial and Temporal Control in Precision Cyclic Vinyl Polymer Synthesis by Lewis Pair Polymerization

Abstract

In typical cyclic polymer synthesis via ring‐closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.

Use of anN-heterocyclic carbene (NHC)-based interacting Lewis pair for the synthesis of a cyclic poly(alkyl acrylate)viachain-growth polymerization and subsequent ring-closing without extreme dilution

“…S9 †), which did not support our reported nucleophilic pathway but the basic pathway reported by Chen et al. 14 When EA was used as the monomer, the formation of the linear polymer in addition to the cyclic polymer was confirmed by 1 H-NMR spectroscopy (Fig. S10 †) and MALDI-TOF mass analysis (Fig.…”

“…S9†), which did not support our reported nucleophilic pathway but the basic pathway reported by Chen et al . 14…”

“…Recently, Chen et al reported a revised initiation mechanism in the same polymerization, in which NHC t Bu abstracted the ε-methyl proton of ethyl sorbate(ES) as the base and the produced anion acted as the propagating center to give cyclic poly(ES) via Michael addition of the anion towards the α-terminal ES unit (Scheme 1). 14 They called the corrected synthetic route the “basic pathway” 14 in contrast to our reported “nucleophilic pathway” 13 by NHC t Bu and the latter is discredited now. The neighboring of α-terminal deprotonated sorbate unit with the propagating anion in the mechanisms enables cyclization without highly diluted conditions.…”

Compounded Interplay of Kinetic and Thermodynamic Control over Comonomer Sequences by Lewis Pair Polymerization

“…Most recently, we detailed a mechanistic study on the precision synthesis of cyclic vinyl polymers in which the fundamental mechanisms in LPP that underly CSC were shown to enable spatial and temporal control in the synthesis of cyclic homopolymers and BCPs. 23 The two-step propagation mechanism of LPP (Figure 1), 4 wherein a free monomer is first coordinated to an equivalent of LA (monomer activation) and then the activated monomer undergoes nucleophilic attack by the active polymeric growing chain (monomer addition), enables CSC and the bulk of the additional polymerization control bolstered by LPP. This twostep propagation presents itself kinetically as a zero-order monomer decay profile characterized by a rate of polymerization = k p [LA] 0 [LB] 0 .…”

“…We have also reported that n BA and methyl methacrylate (MMA) are highly compatible for CSC and produce (near) perfect AB sequences (P n BA- b -PMMA) with either linear or cyclic block copolymer (BCP) topologies, thus establishing that CSC between different monomer classes is also possible. Most recently, we detailed a mechanistic study on the precision synthesis of cyclic vinyl polymers in which the fundamental mechanisms in LPP that underly CSC were shown to enable spatial and temporal control in the synthesis of cyclic homopolymers and BCPs …”