Homo- to Co-Polyester Conversion in the Absence of Reagents Fa-cilitated by a Dual Catalytic Process Involving Hydrogen Borrowing

A ruthenium-catalyzed hydrogen transfer ester metathesis (HTEM) is reported that allows for the isomerization of a linear polyester such as polycaprolactone (PCL) without the need for any stoichiometric reagent, forming a novel type of co-polyester containing additional hexylene adipate (HA) repeating units. Mechanistic investigations show that the formation of the chemically modified polyester relies on a two-fold catalytic reaction; a HTEM via a hydrogen borrowing process and a concomitant transesterification catalyzed by the base co-catalyst. Evidence is provided that the hydrogen transfer ester me-tathesis proceeds via a reversible aldehyde formation. The described HTEM represents an unprecedented catalyzed hydrogen borrowing process within polymers – and bears significant importance regarding a dynamic post-synthetic modification of polyesters.