(Meth)acrylate-Free Three-Dimensional Printing of Bio-Derived Photocurable Resins with Terpene- and Itaconic Acid-Derived Poly(ester-thioether)s

Vat photopolymerization, a very efficient and precise object manufacturing technique, still strongly relies on the use of acrylate- and methacrylate-based formulations because of their low cost and high reactivity. However, the environmental impact of using fossil fuel-based, volatile, and toxic (meth)acrylic acid derivatives is driving the scientific community toward the development of alternatives that can match the mechanical performance and three-dimensional (3D) printing processability of traditional photocurable mixtures but are made from environmentally friendly building blocks. Herein, itaconic acid is polymerized with polyols derived from naturally occurring terpenes to produce photocurable poly(ester-thioether)s. The formulation of such polymers using itaconic acid-based reactive diluents allows the preparation of a series of (meth)acrylate-free photocurable resins, which can be 3D printed into solid objects. Extensive analysis has been conducted on the properties of photocured polymers including their thermal, thermomechanical, and mechanical characteristics. The findings suggest that these materials exhibit properties comparable to those of traditional alternatives that are created using harmful and toxic blends. Notably, the photocured polymers are composed of biobased constituents ranging from 75 to 90 wt %, which is among the highest values ever recorded for vat photopolymerization applications.

STED-Inspired Cationic Photoinhibition Lithography

Direct laser writing by two-photon lithography has been enhanced substantially during the past two decades by techniques borrowed from stimulated emission depletion (STED) microscopy. However, STED-inspired lithography was so far limited to radical polymerizations, mostly to acrylates and methacrylates. Cationic polymers did not derive benefits from this technique. Specifically, epoxide polymerization, which plays a paramount role in semiconductor clean-room technology, has not yet been reported with a second, depleting laser focus in the outer rim of the point spread function. We now found that using a thioxanthone as a sensitizer and sulfonium or iodonium salts as photoinitiators enables at least partial optical on/off switching of two-photon polymerization and, in the case of the sulfonium salt, allows for writing epoxy lines with widths shrunk by approx. two-thirds compared to lines written with two-photon polymerization alone.

Photoredox Catalysis with Visible Light for Synthesis of Thioxanthones Derivatives

A visible-light-promoted and transition-metal-free photoredox-catalysis strategy is developed for the synthesis of thioxanthone derivatives (TXs). The mechanistic study and density functional theory calculations suggest that visible-light-promoted intramolecular cyclization can be divided into hydrogen atom transfer, C-C formation, and oxidative dehydrogenation with high regioselectivity and reactivity. Significantly, this C-C formation strategy can be used in TXs-based commercial photoinitiators and drugs at the gram level.

High-Performance Photoinitiating Systems for LED-Induced Photopolymerization

Currently, increasing attention has been focused on light-emitting diodes (LEDs)-induced photopolymerization. The common LEDs (e.g., LED at 365 nm and LED at 405 nm) possess narrow emission bands. Due to their light absorption properties, most commercial photoinitiators are sensitive to UV light and cannot be optimally activated under visible LED irradiation. Although many photoinitiators have been designed for LED-induced free radical polymerization and cationic polymerization, there is still the issue of the mating between photoinitiators and LEDs. Therefore, the development of novel photoinitiators, which could be applied under LED irradiation, is significant. Many photoinitiating systems have been reported in the past decade. In this review, some recently developed photoinitiators used in LED-induced photopolymerization, mainly in the past 5 years, are summarized and categorized as Type Ⅰ photoinitiators, Type Ⅱ photoinitiators, and dye-based photoinitiating systems. In addition, their light absorption properties and photoinitiation efficiencies are discussed.

Recent progress in the development of highly active dyeing photoinitiators based on 1,3-bis(p-substituted phenylamino)squaraines for radical polymerization of acrylates

The photopolymerization is a very popular technique used in the production of various polymeric materials. The key role in the light induced polymerization processes plays a photoinitiator. One of the...