Lipase Catalyzed HEMA Initiated Ring-Opening Polymerization: In Situ Formation of Mixed Polyester Methacrylates by Transesterification

Abstract

2-Hydroxyethyl methacrylate (HEMA) was used as initiator for the enzymatic ring-opening polymerization (ROP) of omega-pentadecalactone (PDL) and epsilon-caprolactone (CL). The lipase B from Candida antarctica was found to catalyze the cleavage of the ester bond in the HEMA end group of the formed polyesters, resulting in two major transesterification processes, methacrylate transfer and polyester transfer. This resulted in a number of different polyester methacrylate structures, such as polymers without, with one, and with two methacrylate end groups. Furthermore, the 1,2-ethanediol moiety (from HEMA) was found in the polyester products as an integral part of HEMA, as an end group (with one hydroxyl group) and incorporated within the polyester (polyester chains acylated on both hydroxyl groups). After 72 h, as a result of the methacrylate transfer, 79% (48%) of the initial amount of the methacrylate moiety (from HEMA) was situated (acylated) on the end hydroxyl group of the PPDL (PCL) polyester. In order to prepare materials for polymer networks, fully dimethacrylated polymers were synthesized in a one-pot procedure by combining HEMA-initiated ROP with end-capping using vinyl methacrylate. The novel PPDL dimethacrylate (>95% incorporated methacrylate end groups) is currently in use for polymer network formation. Our results show that initiators with cleavable ester groups are of limited use to obtain well-defined monomethacrylated macromonomers due to the enzyme-based transesterification processes. On the other hand, when combined with end-capping, well-defined dimethacrylated polymers (PPDL, PCL) were prepared.

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

“…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%).…”

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

“…This is in full analogy with the processes found when using HEMA as the initiator. [26] In lipase catalysis, a covalent intermediate, acyl enzyme, is formed by nucleophilic attack on the carbonyl carbon (in the ester to be cleaved) by the active nucleophile (serine) situated at the active site of the enzyme. In Scheme 1, three different acyl enzymes are illustrated: (A) lipase acylated by the opened monomer; (B) lipase acylated by the (meth)acrylate moiety; (C) lipase acylated by a polyester moiety.…”

“…In a recent study we were able to show that in the HEMA-initiated ROP of PDL and CL, the ester bond within the HEMA participates in the transesterification reactions, resulting in a mixture of polymer products with various end-groups, such as polymers with no, with one and with two methacrylate end-groups. [26] Furthermore, the 1,2-ethanediol moiety (from HEMA) was found within the polyester chains. The extent and thus the distribution of the end-groups were found to depend on the reaction time and the monomer used.…”

Candida antarctica Lipase B as Catalyst for Cyclic Esters Synthesis, Their Polymerization and Degradation of Aliphatic Polyesters

“…Recently, oligomers of PPDL were obtained at 70 and 90 °C for 24 h [84]. PPDL can be also synthesized in the presence of HEMA initiator [85], in order to obtain methacrylated aliphatic polyester, which in further studies can be used for formation of macroporous matrices for tissue scaffolds [86]. Another difunctional poly(ω-PDL) designed for biomedical application was prepared by solvent free ROP of PDL in the presence of 4 wt% of N-435 and initiated by 6-mercapto-1-hexanol and terminated by γ-thiobutyrolactone or vinyl acrylate (Scheme 4e) [87].…”