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Generally the idea with photopolymers as used with resin 3D printing is that the process only works in a single direction as with all thermosets: after polymerization under influence of UV light they become an inert lump of plastic. Being able to turn these lumps back into resin would of course be ideal, as it would make recycling incredibly easy. Here depolymerizable resin turns out to be a thing, with 3Dresyn being one company that sells additives and resin which enable this (found via Fabbaloo).
Irreversible (thermoset), partial and full depolymerization. (Credit: Machado et al., Nature, 2024)
These additives and resins come in essentially two flavors based on which temperature they depolymerize at, which can be at either 80°C or 150°C. This comes at a cost, of course, with the ready-to-use resin coming in at an eyewatering €833.00 for a 1 kg bottle, a factor only slightly helped by the reusability aspect.
From a more technical perspective this depolymerization feature is fascinating, as it addresses the one aspect of thermosets (like SLA and epoxy resins) that thermoplastics have as advantage, especially from a recycling view. This type of circular photopolymer appears to be quite novel, with an article by [Machado] et al. from 2024 claiming to have demonstrated the first resin that can be photopolymerized, depolymerized and subsequently again photopolymerized in a closed loop.
