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

Abstract

This work presents a robust method to achieve the synthesis of low molecular weight polyesters via ring‐opening polymerization (ROP) initiated by 2‐hydroxyethyl‐methacrylate (HEMA) when using triazabicyclodecene (TBD) as catalyst. The effect that the HEMA:TBD ratio has upon the final reaction rate and final polymer molecular architecture is discussed. The optimum HEMA:TBD ratio and reaction conditions required to minimize competing transesterification reactions are determined, in order to synthesize successfully the target ROP macromonomer species containing only a single 2‐methacryloyloxyethyl end‐group. Additionally, to confirm the terminal end‐group fidelity of the product macromonomers and confirm TBD utility for block copolymer manufacture, a small series of di‐block polyesters are synthesized using TBD and shown to exhibit good control over the final polymer structure whilst negating the side transesterification reactions, irrespective of the monomers used.

Versatile, Highly Controlled Synthesis of Hybrid (Meth)acrylate–Polyester–Carbonates and their Exploitation in Tandem Post‐Polymerization–Functionalization

“…An NMR kinetic study was undertaken to assess the susceptibility of two model methacrylate initiators, HEMA and PEGMA, to transesterification whilst in the presence of DBU. Previously, targeting a DPn below 35 was found to be unachievable with TBD as catalyst and HEMA as initiator due to transesterification side‐reactions . However, in this work, the kinetic study employing an amount of DBU with HEMA or PEGMA to target a final DPn of 5 did not result in any observable transesterification side‐reactions ( Figure ; Figure S1, Supporting Information).…”

“…Labile‐ester initiators are well known to exhibit, particularly at high initial initiator concentrations, a tendency to undergo transesterification (Scheme S1, Supporting Information) in the presence of active and bifunctional ROP catalysts such as lipase and TBD . This susceptibility significantly limits the molecular weights and polymer architectures that can be targeted via ROP.…”

“…In this regard, we have previously demonstrated the use of triazabicyclodecene (TBD) and 1,8‐diazabicyclo[5.4.0]undec‐5‐ene (DBU) as organocatalysts for the synthesis of PEG and HEMA‐initiated polyesters and polycarbonates, demonstrating good control over the final polymer architectures when employing optimised reaction conditions . However, despite the high catalytic activity of TBD, when low molecular weight materials (<2500 Da) were targeted, the kinetics of transesterification prevailed over the ROP process, limiting the synthetic strategy toward accessing oligomeric species . In addition, TBD has the tendency to cleave BOC‐protected functionalities, leading to a fast self‐immolative degradation of the growing polymer chain when used in the presence of functional monomers …”

“…However, despite the high catalytic activity of TBD, when low molecular weight materials (<2500 Da) were targeted, the kinetics of transesterification prevailed over the ROP process, limiting the synthetic strategy toward accessing oligomeric species . In addition, TBD has the tendency to cleave BOC‐protected functionalities, leading to a fast self‐immolative degradation of the growing polymer chain when used in the presence of functional monomers …”

Role of self‐assembly conditions and amphiphilic balance on nanoparticle formation of PEG‐PDLLA copolymers in aqueous environments

“…However, a major drawback with LA‐based polymers and copolymers is the toxic catalyst and stringent reaction conditions typically utilized in their production . Recently, we demonstrated a more friendly catalytic approach for ROP of LA in ambient conditions and at room temperature, using mild organocatalysts such as 1,8‐diazabicyclo[5.4.0]undec‐5‐ene (DBU) . This synthetic approach negates the need for toxic catalysts, high temperature reactions (over 120°C), and more extensive purifications, thereby facilitating further access to these materials across nonspecialist chemical laboratories.…”