Systematic Comparison of HEA and HEMA as Initiators in Enzymatic Ring‐Opening Polymerizations

Abstract

Two initiators containing a cleavable ester bond were compared in the lipase-catalyzed ROP of CL and PDL. The results show that transesterification reactions are present at high rates throughout the enzymatic ROP and start at low conversion. HEA and HEMA displayed similar reaction efficiencies as initiators (acyl acceptors) in the enzymatic ROP. However, transacylation reactions on the HEA-initiated polyesters were found to be 15 times faster. While in both cases the amount of HEA- and HEMA-initiated polymers could be maximized by short reaction times, a well-defined (meth)acrylation by this approach was not possible. Our results show that transesterification reactions have to be considered when performing an enzyme-catalyzed ROP.

Synthesis of Methacrylate‐Terminated Block Copolymers with Reduced Transesterification by Controlled Ring‐Opening Polymerization

“…This study has also concluded that TBD is a more efficient ROP catalyst when compared to lipases. In fact, it has been well documented that lipases cannot discriminate ROP from the transesterification sub‐processes in the presence of cleavable ester initiators such as HEMA, even at low monomer conversion . This leads to the production of di‐methacrylated macromolecular chains and an inability to produce well‐defined polymers.…”

“…An alternative route to polyesters utilizes enzymes as the catalyst system . However, enzyme‐catalyzed ROP (eROP) generally results in slow reactions with limited control over the final polymer architecture . In HEMA‐initiated Lipase catalyzed eROP, even at low monomer conversion, numerous unwanted by‐products are routinely obtained.…”

“…In HEMA‐initiated Lipase catalyzed eROP, even at low monomer conversion, numerous unwanted by‐products are routinely obtained. This has been attributed to the low reaction selectivity of the enzyme, which allows competition between ROP and other transesterification processes . The use of triazabicyclodecene (TBD) as a catalyst for ROP has been demonstrated with a variety of cyclic monomers, resulting in the synthesis of polymers with controlled molecular weight and polydispersity .…”

Hydrolases Part I: Enzyme Mechanism, Selectivity and Control in the Synthesis of Well-Defined Polymers

“…Vinyl(meth)acrylates were also found to be suitable end-cappers during the polymerization reactions [70,119]. In combination with HEMA or HEA as an initiator, di(meth)acrylate macromonomers are accessible in a one-pot enzymatic procedure [58,79,81]. In addition, in a one-pot approach, glycidol initiation in combination with a divinyl ester initiator also resulted in epoxide end-capped polyesters that can be cured into biodegradable coatings [111].…”

“…perform reactions under equilibrium conditions), allows high endgroup fidelity in a lipase-catalyzed ROP, even in a one-pot procedure [58,80,111,112,[116][117][118]. Initiation with mercapto-ethanol or 6-mercapto-1-hexanol in lipasecatalyzed ROP of CL and ω-pentadecanolactone (PDL), respectively, resulted in high initiator incorporation (95%).…”