Blocked Phosphates as Photolatent Catalysts for Dynamic Photopolymer Networks

A photolatent organophosphate is synthesized and introduced into a resin system, which is 3D printed with visible light. The subsequently UV-released transesterification catalyst activates dynamic exchange reactions at elevated temperatures. Without affecting the thermal stability of the polymer network, bond exchange reactions and shape memory can be spatiotemporally controlled.

Abstract

While latent catalysts are a well-established strategy for initiating and controlling the rate of polymerization reactions, their use in dynamic polymer networks is still in its infancy. The ideal latent catalyst should be thermally stable and release a highly active species in response to an external trigger. Here, we have synthesized a temperature resistant (>200 °C) organic phosphate with a photolabile o-nitrobenzyl protecting group that can be cleaved by UV light. Introduced in a visible light curable thiol-click photopolymer, the sequence-dependent λ-orthogonality of the curing and cleavage enables an efficient network formation at 451 nm, without premature release of the catalyst. Once cured, irradiation at 372 nm spatiotemporally activates the phosphate, which catalyzes transesterifications at elevated temperature. The formed catalyst has no effect on the thermal stability of the polymeric network and allows the activation of bond exchange reactions in selected domains of printed 3D objects.

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