Lewis Pair Polymerization of Renewable Indenone to Erythro-Ditactic High‑T g Polymers with an Upcycling Avenue

• Published in: Macromolecules 2020-01, Vol.53 (2), p.640-648
• Main Authors: Clarke, Ryan W, McGraw, Michael L, Gowda, Ravikumar R, Chen, Eugene Y.-X
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.9b02285

Preparation and storage of biorenewable, monomeric indenone, much less the polymerization to a well-defined, high-molecular-weight polymer, is challenging because of antiaromaticity-driven radical autopolymerization. Herein, we report the successful preparation and subsequent Lewis pair polymerization (LPP) of indenone without autopolymerization side reactions using Lewis pairs consisting of sterically encumbered Lewis acid (LA) catalysts, such as B­(C6F5)3 and bis­(2,6-tert-butyl-4-methylphenoxy)­methylaluminum and Lewis base initiators such as silyl ketene acetal and N-heterocyclic olefin nucleophiles. Thus, for the first time, the LPP enabled the synthesis of polyindenone (Pin) with high number-average molecular weight (M n = 1.72 × 105 g mol–1) and low dispersity (D̵ = 1.13). Observed correlations between the steric bulk of the LA catalyst and diastereoselectivity (57–75%) created the opportunity to model and investigate the relationships between β-substituted monomer motifs, catalyst steric accessibility, and the propagation stereodefining step for ensuing ditactic assignments. Through the increased erythro-diastereoselectivity, semicrystalline materials were produced with remarkably high glass-transition temperatures (T g = 307 °C), high thermal stability (T d,5% = 356 °C), and competitive transmittance (T %) and haziness values (T % = 85–88%, haze = 11%). Controlled pyrolysis of Pin upconverted it into versatile graphite oxide with 54% conversion, offering an upcycling avenue for Pin at the end of its life.