Sigmatropic Rearrangements of Polymer Backbones: Vinyl Polymers from Polyesters in One Step

Abstract

Polymer modification is a fundamental scientific challenge, as a means of both upcycling plastics and extracting a stimulus response from them. To date, the overwhelming majority of polymer modifications has focused on the polymer periphery. Herein, we demonstrate nearly quantitative, scission-free modification of polymer backbones, namely, a metamorphosis of polyesters into vinyl polymers resembling commodity materials via the Ireland–Claisen sigmatropic rearrangement. The glass transition temperature (T g) and thermal stability of the polyesters undergo dramatic changes post-transformation. Beyond polymer modification, our work advances the application of retrosynthetic analysis in polymer synthesis; the nontraditional production of vinyl polymers from lactones opens the door to a slew of previously inaccessible materials.

Advancing the Logic of Polymer Synthesis via Skeletal Rearrangements

“…10 Furthermore, the thermal stability, as judged by thermogravimetric analysis, substantially increased on converting polyesters into vinyl polymers. 10 The predictability of these changes, coupled to the efficiency of the rearrangements, highlights the potential of this strategy to design stimulus-responsive behavior into soft materials.…”

“…20 in the case of ADMET and 40-43 in the case of ROTEP (Scheme 5A, B). 10,11 Scheme 5 A, B. Synthesis of model precursor polymers P1 (A) and P2, P3 (B). Sigmatropomers are highlighted in red.…”

“…The model precursor polymers were prepared through acyclic diene metathesis (ADMET) copolymerization of 1,9-decadiene and an acyl silane-containing diene M1 11 and ring-opening transesterification polymerization (ROTEP) of ω-vinyllactones M2 and M3 10 (Scheme 5 A, B). Despite the simplicity of their chemical structure, M1 , M2 , and M3 had not been polymerized previously; brief optimization of polymerization conditions was sufficient to produce the corresponding polymers P1 , P2 , and P3 in ca.…”

“…Crucially, the precursor polymer backbones must incorporate moieties that would undergo the sigmatropic rearrangements, which we refer to as ‘sigmatropomers’ (Scheme 4 A, B). 10 In the case of poly(acyl silane)s, the sigmatropomers are just the acyl silane groups; in the case of the polyesters, the sigmatropomers are allylic esters. Notably, while the Ireland–Claisen rearrangement is sigmatropic, the Brook rearrangement, strictly speaking, is not: C-to-O migration of the silyl group proceeds via a pentacoordinate silicate intermediate, and therefore is not concerted.…”

“…Two recent contributions from our laboratory showcase the power of retrosynthetic analysis applied to polymer synthesis ( vide infra ). 10 11 A common conceptual thread that runs through both reports is that if ‘poly(X)’ cannot be readily prepared from ‘X’, it may instead be derived from ‘poly(Y)’ through skeletal editing (Scheme 1 B) – a process that alters which atoms are connected to make the polymer backbone (i.e., the skeleton). Such a disconnection provides new and potentially more sustainable pools of monomers ‘Y’ for existing materials and enables construction of novel materials previously inaccessible through conventional means (Scheme 1 B).…”