More and more coatings, including varnishes and printing inks, as well as dental fillings, are photocured. However, it is not possible to produce a uniform polymer network, and the material tends to be brittle, which limits the photopolymer in three dimensions. Applications in the fields of printing, biomedical and microelectronics. In the Angewandte Chemie journal, researchers have proposed a new method, based on methacrylate, to make a uniform cross-linking tough polymer, even at high resolution for 3D printing.
Photocuring is usually a radical chain polymerization. The initiator is decomposed into free radicals by light energy and attacks the monomer, such as the C=C double bond in the vinyl group, forming a new free radical, by attacking more singles. And combine with it to become the starting point of polymer network growth.
New methods of controlling free radical photopolymerization and improving the material properties of the product tend to slow down the curing process, which is not ideal for 3D printing. The short illumination phase is critical for high spatial resolution and economical production time. .
A research team led by Robert Liska of the Technical University of Vienna (Austria) developed a new method. Methacrylate-based photopolymers do not inhibit the curing process. They use ester-activated vinyl sulfonate (EVS) as a chain transfer agent because it can be easily separated from its own part to activate the process. .
If a growing polymer network attacks EVS instead of another monomer, an intermediate is formed and rapidly splits to form a terminated polymer chain and a highly reactive group (tosyl) in the network, which in turn A new chain reaction will be triggered. The more EVS added, the shorter the average chain length of the polymer network. Since the shorter polymer chains maintain a longer mobility, the risk of cracking during the curing process is marked. Decrease Contrary to conventional chain transfer agents, polymerization is not inhibited in this new process, since the presence of stable intermediates or reversible reaction steps is advantageous, so it is advantageous to isolate the tosyl group.
To test it, the researchers used a methacrylate copolymer to create a stent-like sample structure. The thickness is 50 μm, which is well resolved in the structure in each layer. The material is very uniform, strong but elastic and impact resistant. High tensile strength. These properties can be adjusted by changing the number of added EVS. Without EVS, the material will be too brittle to be 3D printed. This new method produces tough photopolymers for biomedical applications such as shape memory polymers for tissue growth and tooth filling.