The click reaction paradigm is focused on the development and implementation of reactions that are simple to perform while being robust and providing exquisite control of the reaction and its products. Arguably the most prolific and powerful of these reactions, the copper-catalysed alkyne-azide reaction (CuAAC) is highly efficient and ubiquitous in an ever increasing number of synthetic methodologies and applications, including bioconjugation, labelling, surface functionalization, dendrimer synthesis, polymer synthesis and polymer modification. Unfortunately, as the Cu(I) catalyst is typically generated by the chemical reduction of Cu(II) to Cu(I), or added as a Cu(I) salt, temporal and spatial control of the CuAAC reaction is not readily achieved. Here, we demonstrate catalysis of the CuAAC reaction via the photochemical reduction of Cu(II) to Cu(I), affording comprehensive spatial and temporal control of the CuAAC reaction using standard photolithographic techniques. Results reveal the diverse capability of this technique in small molecule synthesis, patterned material fabrication and patterned chemical modification.

Developing chemically recyclable polymers represents ag reener alternative to landfill and incineration and offers ac losed-loop strategy towardacircular materials economy.H owever,t he synthesis of chemically recyclable polymers is still plagued with certain fundamental limitations, including trade-offs between the monomersc yclizability and polymerizability,a sw ell as between polymersd epolymerizability and properties.H ere we describe the subtle O-to-S substitution, dithiolactone monomers derived from abundant feedstock a-amino acids can demonstrate appealing chemical properties different from those of dilactone,i ncluding accelerated ring closure,a ugmented kinetics polymerizability,h igh depolymerizability and selectivity,and thus constitute aunique class of polythioester materials exhibiting controlled molecular weight (up to 100.5 kDa), atactic yet high crystallinity, structurally diversity,a nd chemical recyclability.T hese polythioesters well addresses the formidable challenges of developing chemically recyclable polymers by having an unusual set of desired properties,i ncluding easy-to-make monomer from ubiquitous feedstock, and high polymerizability,c rystallinity and precise tunability of physicochemical performance,aswell as high depolymerizability and selectivity.C omputational studies explain why O-to-S modification of polymer backbone enables dovetailing desirable,but conflicting,performance into one polymer structure. Figure 1. Strategies for the synthesis of recyclablep olymers.

Ring-opening polymerization of O-carboxyanhydrides (OCAs) can furnish polyesters with a diversity of functional groups that are traditionally hard to harvest by polymerization of lactones. Typical ring-opening catalysts are subject to unavoidable racemization of most OCA monomers, which hampers the synthesis of highly isotactic crystalline polymers. Here, we describe an effective bifunctional single-molecule organocatalysis for selective ring-opening polymerization of OCAs without epimerization. The close vicinity of both activating groups in the same molecule engenders an amplified synergetic effect and thus allows for the use of mild bases, thereby leading to minimal epimerization for polymerization. Ring-opening polymerization of manOCA monomer (OCA from mandelic acid) mediated by the bifunctional single-molecule organocatalyst yields highly isotactic poly­(mandelic acid) (PMA) with controlled molecular weights (up to 19.8 kg mol–1). Mixing of the two enantiomers of PMA generates the first example of a crystalline stereocomplex in this area, which displayed distinct T m values around 150 °C. Remarkably, the bifunctional catalysts are moisture-stable, recyclable, and easy to use, allowing sustainable and scalable synthesis of a stereoregular functional polyester.