Catalyst-Free Partially Bio-Based Polyester Vitrimers

TLDR

Vitrimers based on ester linkages typically require Lewis acid or strong organic base catalysts, and their recyclability depends on catalyst retention, stability, and sintering. The authors synthesize β‑activated ester vitrimers by reacting poly(hydroxyethyl methacrylate) with malonic ester precursors, enabling catalyst‑free thermal reprocessing. The β‑activated ester vitrimers can be thermally reprocessed at ~150 °C without a catalyst, exhibit tensile strengths of 11.3–33.0 MPa, elongations of 80–290 %, self‑heal, and retain properties after reprocessing, while Sn(Oct)₂‑modified analogues reprocess at ~110 °C and show comparable mechanical performance, suggesting utility in coatings, hydrogels, biomaterials, adhesives, and plastics.

Abstract

Most of the vitrimers based on ester linkages reported so far contain a Lewis acid or a strong organic base as the transesterification catalyst. The recyclability and reusability of these vitrimers are dependent on the catalyst retention, stability, and sintering issues. Herewith, a set of β-activated ester-based vitrimers are reported that can be thermally reprocessed at ∼150 °C under catalyst-free conditions. The relaxation temperature decreases to 110 °C in the presence of Sn(Oct)2. Importantly, the precursor of these vitrimers, malonic ester, is a cost-effective naturally occurring ester and can be extracted from various fruit juices. As a proof of concept, poly(hydroxyethyl methacrylate) is used as the hydroxyl precursor for the synthesis of vitrimers. These vitrimers display an adequate tensile strength (11.3–33.0 MPa), elongation (80–290%), and resilience. The materials can be effectively self-healed and reprocessed in the presence of heat without sacrificing the tensile properties. The vitrimers based on Sn(Oct)2 exhibit mechanical properties similar to that of the catalyst-free analogues and reprocess at ∼110 °C. These vitrimers may potentially be utilized for the development of coatings, hydrogels, biomaterials, adhesives, and commodity plastics in the future.