Unveiling the reverse reactivity and composition profile of copolymers from synthesized and separated 3-/7-(prop-2-ynyl)oxepan-2-one isomers: implications for precise polymer structure prediction

Abstract

The structure–property relationship of synthetic polymers is crucial for the design of their synthesis. Synthesis design determines the final behavior and thus potential applications of the material. However, structurally assessing a synthetic polymer at the level of monomeric sequences remains challenging. Here, we report the kinetic investigation of the reactivity between 3- and 7-(prop-2-ynyl)oxepan-2-one during their copolymerization. These monomers are mainly used to synthesize biomedical materials without separating the isomers, which can lead to undesirable composition drift, thereby affecting the resulting properties. Nevertheless, we separated both isomers and studied their polymerization kinetics in detail. Our screening (co)polymerization experiments revealed the reverse reactivity of 3- and 7-isomers during their homo- and copolymerization. Moreover, based on kinetic data, we calculated copolymerization parameters using the Integrated Ideal Model developed by Frey et al. and visualized the composition profile of the copolymers. By combining kinetic experiments and quantum chemical methods with state-of-the-art analytical techniques, including nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), differential scanning calorimetry (DSC) and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS), we identified the gradient copolymer structure, whereinto the slowly reacting 3-isomer was incorporated at the late stage of copolymerization. Therefore, our findings may become a useful tool for structural predictions of (co)polymers consisting of these isomers, ultimately opening up further opportunities for their biomedical applications.