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S. Schörpf, Y. Catel, N. Moszner, C. Gorsche, R. Liska:
"Reduction of polymerization-induced shrinkage stress via combination of radical ring opening and addition fragmentation chain transfer";
Vortrag: 5th European Symposium of Photopolymer Science, Mulhouse, France; 03.09.2018 - 06.09.2018; in: "5th European Symposium of Photopolymer Science", 5th European Symposium of Photopolymer Science, (2018), S. 13.

Photoinitiated methacrylate (MA) systems suffer from shrinkage stress, which is a restricting factor in various applications (e.g. coatings, 3D-printing and dentistry).1-3 The occurring shrinkage stress can lead to delamination, deformation or mechanical failure of the final material. Furthermore, the resulting materials tends to show brittle behavior.
The shrinkage stress upon gelation is due to the replacement of the Van der Waals distance of the monomers, before the polymerization, by covalent bonds. The distance of the monomers is approximately 3.4 Å in the unpolymerized state, after polymerization when the covalent bond is formed the revealing distance is only 1.5 Å.4
One option to reduce the shrinkage stress is to replace the methacrylates by vinylcyclopropanes (VCPs).5 The VCPs undergo a radical ring opening polymerization (RROP) during curing which leads to a lower shrinkage stress. To counteract the undefined network structure, which is generated by the early gelation at low conversions, chain transfer agents (AFCTs) can be used. The ester activated vinyl sulfonate ester (EVS) enables the generation of a more homogenous network and a shift of the gel point to higher conversions.6
The combination of both methods demonstrates a promising technique to reduce the overall shrinkage stress of a polymerizing network even more. During the curing process, VCPs undergo RROP while the EVS regulates the network and shifts the gel point to higher conversions. This combination leads to more homogenous networks and a significant reduction of shrinkage stress compared to unregulated MA systems. In addition, the reactivity could be increased without compromising mechanical properties.

shrinkage stress, Photoinitiated methacrylate, coatings, 3D-printing and dentistry, delamination, deformation or mechanical failure of the final material, brittle behavior, replace the methacrylates by vinylcyclopropanes