Synthesis of Pyridine- and 2-Oxazoline-Functionalized Vinyl Polymers by Alane-Based Frustrated Lewis Pairs

Abstract

Reported herein is the first example of polymerization of polar vinyl monomers bearing the C=C-C=N functionality by Frustrated Lewis pairs (FLPs). In particular, FLPs based on Al(C 6 F 5 ) 3 and N-heterocyclic carbenes rapidly convert 2-vinyl pyridine and 2-isopropenyl-2-oxazoline into medium to high molecular weight, Nfunctionalized vinyl polymers. Activated monomer-alane adduct 1 and initiated zwitterionic intermediate 2 have been isolated and structurally characterized, providing strong evidence for the proposed bimolecular, activated monomer polymerization mechanism.

Chemoselective Lewis pair polymerization of renewable multivinyl-functionalized γ-butyrolactones

“…The FT-IR spectra of P γ VMMBL and P γ AMMBL (electronic supplementary material, figures S8 and S9) provided corroborative evidence, featuring the absorption bands corresponding to the pendant C=C bonds [P γ VMMBL: 3091 (=CH 2 str), 1644 (C=C str), 992 and 929 The chemoselectivity in the Lewis pair polymerization of γ VMMBL and γ AMMBL originates from the pathway that proceeds through polyaddition to the vinyl group conjugated with the carbonyl moiety, which is activated via coordination of the carbonyl to the LA, while leaving the non-conjugated vinyl or allyl group unperturbed, thereby yielding chemoselective polymerization and leading to soluble P γ VMMBL and P γ AMMBL polymers (scheme 2). This is consistent with the Lewis pair polymerization known to proceed via a bimolecular, activated monomer propagation mechanism [21,74]. Accordingly, considering γ VMMBL as an example, a propagating step is proposed to involve nucleophilic attack of the activated γ VMMBL (adduct B) by zwitterion A and its homologues; the LA attached to the antepenultimate γ VMMBL unit after each addition step is regained by the incoming monomer, and the successive conjugate addition in such a propagating step yields the high-molecular-weight P γ VMMBL (scheme 2).…”

“…Organopolymerization [42][43][44][45] has become an important method of polymer synthesis, especially when metal-free products or processes are of main interest. For example, since the pioneering work of Hedrick and Waymouth et al [46][47][48], N-heterocyclic carbene (NHC) mediated polymerization [49][50][51][52] has advanced considerably to cover now not only the ringopening polymerization of heterocyclic monomers [53][54][55][56], but also step-growth polymerization [57][58][59], chain-growth addition polymerization of linear (acrylates, methacrylates) [60][61][62] and cyclic acrylic monomers (MMBLs) [63][64][65][66], group-transfer polymerization [67][68][69][70], Lewis pair polymerization [19][20][21][71][72][73][74][75][76] and proton-transfer polymerization [77,78]. We have recently reported the organocatalytic and chemoselective polymerization of multivinyl-functionalized γbutyrolactones, including VMBL, γ-vinyl-β-methyl-α-methylene-γ-butyrolactone and DAMBL, with NHCs [66].…”

Organoboron-mediated polymerizations

“…However, they still found that the reaction of the system of LP containing B atoms with the corresponding monomers only formed zwitterionic compounds, which did not show any catalytic activity for the following polymerization. 112,[116][117][118][119] It was not until 2014 Chen and Xu reported a significant breakthrough in the active polymerization of the renewable monomer MMBL using organoboron-based Lewis pairs (Fig. 25).…”

“…However, they still found that the reaction of the system of LP containing B atoms with the corresponding monomers only formed zwitterionic compounds, which did not show any catalytic activity for the following polymerization. 112,116–119…”

Atom Transfer Radical Polymerization of 2-Isopropenyl-2-Oxazoline in Solution and from the Surface of Carbonyl Iron Particles toward Fabrication of a Cytocompatible Magneto-Responsive Hybrid Filler

“…However, cationic ring opening polymerization through the 2-oxazoline ring, leading to pendant vinyl groups, does not provide polymers in a controlled way due to possibility of the crosslinking through the unsaturated bond in the side chain . Polymerization through the double bond of the IPOx was typically performed using free/radical polymerization ,− or frustrated Lewis pair polymerization, , in both cases resulting in polymers with high dispersity. In order to achieve well-defined polymers, living anionic polymerizations ,, or rare earth metal-mediated group transfer polymerizations , could be used.…”