Electronic Effects of Aluminum Complexes in the Copolymerization of Propylene Oxide with Tricyclic Anhydrides: Access to Well-Defined, Functionalizable Aliphatic Polyesters

Abstract

The synthesis of well-defined and functionalizable aliphatic polyesters remains a key challenge in the advancement of emerging drug delivery and self-assembly technologies. Herein, we investigate the factors that influence the rates of undesirable transesterification and epimerization side reactions at high conversion in the copolymerization of tricyclic anhydrides with excess propylene oxide using aluminum salen catalysts. The structure of the tricyclic anhydride, the molar ratio of the aluminum catalyst to the nucleophilic cocatalyst, and the Lewis acidity of the aluminum catalyst all influence the rates of these side reactions. Optimal catalytic activity and selectivity against these side reactions requires a careful balance of all these factors. Effective suppression of undesirable transesterification and epimerization was achieved even with sterically unhindered monomers using a fluorinated aluminum salph complex with a substoichiometric amount of a nucleophilic cocatalyst. This process can be used to synthesize well-defined block copolymers via a sequential addition strategy.

Zinc versus Magnesium: Orthogonal Catalyst Reactivity in Selective Polymerizations of Epoxides, Bio‐derived Anhydrides and Carbon Dioxide

“…The absolute TOF value for 1 (77 h −1 ) is similar to other catalysts for epoxide/anhydride copolymerizations, albeit tested using different anhydrides 6b. Both catalysts show excellent selectivity for ester linkages (>99 %) similar to the most selective and active Al‐salen catalysts reported so far 8q, 8r, 13. Notably, 1 does not require any co‐catalyst as co‐catalysts are known to cause side‐reactions 6b, 8h.…”

Phosphazene/Lewis Acids as Highly Efficient Cooperative Catalyst for Synthesis of High‐Molecular‐Weight Polyesters by Ring‐Opening Alternating Copolymerization of Epoxide and Anhydride

“…However, the monomers used in such ROPs are relatively limited and expensive. Particularly, functional cyclic monomers for preparing polyesters with delicate main‐chain structures and various pendant groups could only be obtained from multiple and complicate synthesis …”

“…Particularly, functional cyclic monomers for preparing polyesters with delicate main-chain structures and various pendant groups could only be obtained from multiple and complicate synthesis. 5 Recently, the ring-opening alternating copolymerization (ROAC) of epoxides and anhydrides has attracted considerable attention as an alternative to prepare polyesters because of its atom-economic reaction and diversity of monomers. 6 With this versatile ROAC, plenty of functional polyesters could be synthesized through valuable green approaches from sustainable resources, 7 which further accelerates its development because of increasing environment/energy considerations.…”

Aluminum Complexes of N2O23– Formazanate Ligands Supported by Phosphine Oxide Donors

“…19 The Coates group produced fluorinated complex 2, which proved to be an effective catalyst for the polymerization of tricyclic anhydrides with minimal side reactivity. 20 The Nabeshima group synthesized dipyrrinate complex 3, which exhibited colourimetric and fluorometric responses to alkaline earth metals. 21 Ma and colleagues designed β-diketiminate complex 4 and demonstrated its use as an effective catalyst for the ring-opening polymerization of cyclic esters.…”