Thermoset polymers pose a serious problem to sustainability initiatives due to their inherent lack of reprocessability. Vitrimers address this limitation by introducing dynamic crosslinks which enable material flow via associative exchange under tailorable conditions (e.g. temperature). Recently, diketoenamine/amine exchanges have emerged as a promising vitrimer chemistry thanks to their rapid, catalyst-free kinetics. While current reports on networks have focused exclusively on amine nucleophiles, they have globally ignored alternative imine chemistries such as oximes or hydrazones. Here we leverage diketoxime crosslinks as a simple, straightforward strategy for controlling important vitrimer properties. We prepared diketoxime networks by first synthesizing an alkene-functionalized diketoxime resin by reacting 5,5-dimethyl-2-(pent-4-enoyl)cyclohexane-1,3-dione with <i>O,O</i>′-1,2-ethanediylbis(hydroxylamine) using a 10% excess of -ONH<sub>2</sub> functional groups to allow for associative exchange. This resin was subsequently cured with pentaerythritol tetrakis(3-mercaptopropionate) and photoinitiator ethyl (2,4,6-trimethylbenzoyl) phenylphosphinate via thiol-ene photopolymerization into 50 μm thick films. This procedure provided soft, optically transparent films which could be subsequently reprocessed into new geometries by heating to 90 °C under 5 MPa of pressure. Importantly, we found that diketoxime-crosslinked networks showed an increase in both activation energy and exchange temperature compared to similar amine-crosslinked systems. Despite these findings however, the reprocessing temperature was comparatively lower indicating the amine systems showing an interesting inversion which we are currently investigating. Our results highlight the importance of materials selection on vitrimer reprocessing, and provide a simple, effective strategy for tuning the vitrimeric properties.

Poly(diketoxime) networks: Adjusting bond exchange to tune vitrimer properties

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