Reactivity Ratios and Mechanistic Insight for Anionic Ring-Opening Copolymerization of Epoxides

• Published in: Macromolecules Vol. 45; no. 9; pp. 3722 - 3731
• Main Authors: Lee, Bongjae F, Wolffs, Martin, Delaney, Kris T, Sprafke, Johannes K, Leibfarth, Frank A, Hawker, Craig J, Lynd, Nathaniel A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 08-05-2012
• Subjects: Applied sciences; Copolymerization; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Preparation, kinetics, thermodynamics, mechanism and catalysts; Kinetic model; Reaction mechanism; Alkoxide; Solution copolymerization; Anionic copolymerization; Glycidyl ether copolymer; Ethylene oxide copolymer; Experimental study; Ring opening copolymerization; Modeling; Reactivity ratio; Allylic compound
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma300634d

Reactivity ratios were evaluated for anionic ring-opening copolymerizations of ethylene oxide (EO) with either allyl glycidyl ether (AGE) or ethylene glycol vinyl glycidyl ether (EGVGE) using a benzyl alkoxide initiator. The chemical shift for the benzylic protons of the initiator, as measured by 1H NMR spectroscopy, were observed to be sensitive to the sequence of the first two monomers added to the initiator during polymer growth. Using a simple kinetic model for initiation and the first propagation step, reactivity ratios for the copolymerization of AGE and EGVGE with EO could be determined by analysis of the 1H NMR spectroscopy for the resulting copolymer. For the copolymerization between EO and AGE, the reactivity ratios were determined to be r AGE = 1.31 ± 0.26 and r EO = 0.54 ± 0.03, while for EO and EGVGE, the reactivity ratios were r EGVGE = 3.50 ± 0.90 and r EO = 0.32 ± 0.10. These ratios were consistent with the compositional drift observed in the copolymerization between EO and EGVGE, with EGVGE being consumed early in the copolymerization. These experimental results, combined with density functional calculations, allowed a mechanism for oxyanionic ring-opening polymerization that begins with coordination of the Lewis basic epoxide to the cation to be proposed. The calculated transition-state energies agree qualitatively with the observed relative rates for polymerization.