Degradation Benefits Polymerization: Photogenerated Self-Degradable Organocatalyst for Higher-Efficiency ATRP and Pure Polymers

In the realm of polymer-based 3D photoprinting, challenges arise from the side effects, notably the persistent presence of photocatalyst residues and metal contamination. These impurities pose significant risks in various applications, including electronics, biological tissues, and medical implants. At the same time, spatial-/time-/light-controlled 3D photoprinting has been hindered by low-efficiency polymerization concerning both initiation and monomer conversion. To address these critical issues, a pioneering concept, "degradation-inhibited quench," is introduced and implemented within photopolymerization to solve the problems mentioned above. This innovative approach aims to produce pure polymers via higher-efficiency atom transfer radical polymerization (ATRP) with a unique class of diketopyrrolopyrrole (DPP) derivatives as organo-photocatalysts at an extremely low concentration (as low as 50 ppm). Through this approach, pure polymers with ultrahigh molecular weight (UHMW) have been successfully synthesized. For instance, poly(methyl methacrylate) (PMMA) achieved a monomer conversion of >50%, a molecular weight of 2.1 million, and a dispersity of 1.38 after 12 h additional dark reaction. Notably, this photopolymerization method demonstrates applicability across a broad spectrum of monomers, with or without solvents, including acrylate, acrylic, styrene, and acrylonitrile. Mechanism insights revealed that the production of UHMW PMMA stemmed from the degradation of intermediate complex DPP center dot+/Br-, which originated from the photoinitiation. This degradation inhibited the oxidative quenching of active propagating chain radicals, thereby significantly extending their lifespan. This groundbreaking concept embraces the potential for further development of highly effective organo-photocatalysts and reactive systems specifically tailored for 3D photopolymerization. Moreover, this spatial-/time-/light-controlled polymerization approach does not require any additional purification, offering energy- and cost-saving manufacturing technology.