Kinetic Analysis of the Immortal Ring-Opening Polymerization of Cyclic Esters: A Case Study with Tin(II) Catalysts

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• 作者：Lingfang Wang ; Valentin Poirier ; Fabio Ghiotto ; Manfred Bochmann ; Roderick D. Cannon ; Jean-Fran莽ois Carpentier ; Yann Sarazin
• 刊名：Macromolecules
• 出版年：2014
• 出版时间：April 22, 2014
• 年：2014
• 卷：47
• 期：8
• 页码：2574-2584
• 全文大小：469K
• 年卷期：v.47,no.8(April 22, 2014)
• ISSN：1520-5835

文摘

A kinetic analysis of the metal-catalyzed immortal ring-opening polymerization (ROP) of cyclic esters is presented, based on a first-principles approach without making assumptions regarding the active species. The kinetics of all immortal ROP reactions performed with a metal catalyst and an exogenous chain transfer agent are characterized by the initiation, propagation and exchange rate constants (k_i, k_p, and k_e, respectively). Curve fitting to this kinetic scheme in the initial stage of the polymerization allows the extraction of k_i and k_p from a single experiment. This has been illustrated for the ROP of l-lactide using tin(II) complexes of the type {LOⁱ}Sn(X) ({LOⁱ} = aminophenolate ancillary ligand, X = N(SiMe₃)₂ or methyl (S,S)-lactate), Sn(OiPr)₂ or Sn(N(SiMe₃)₂)₂ as precatalysts paired with excess iPrOH as a coactivator. Nonlinear regressions (R² > 0.999) illustrate the three possible scenarios, k_i < k_p, k_i = k_p, and k_i > k_p. The kinetic model can be extended to any metal (pre)catalyst for the immortal ROP of any cyclic ester, as exemplified using trimethylene carbonate as a monomer or employing a germylene precatalyst. A kinetic treatment for the late phase of immortal ROP reactions is introduced, which also gives direct access to k_p. In agreement with the ROP kinetic data for {LOⁱ}Sn(N(SiMe₃)₂), Sn(OiPr)₂, Sn(N(SiMe₃)₂)₂, and the new Sn(OiPr)(N(SiMe₃)₂ recorded in the presence of various quantities of iPrOH, synthetic and ¹¹⁹Sn{¹H} NMR data provide evidence for reversible production of tin(II) bis(alkoxide) when a small excess (1鈥? equiv) of alcohol is used with tin(II) precatalysts. It is also shown that, regardless of the identity of the precatalyst, Sn(OiPr)₂ and Sn(O-polymeryl)₂ are, respectively, the actual initiating and propagating species when immortal ROP reactions are performed in the presence of a larger excess of alcohol (7 equiv or more vs Sn).