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J. Steindl, N. Moszner, C. Gorsche:
"Using Silane-ene Chemistry for Chain Transfer in Radical Photopolymerization";
Poster: XXII. Bratislava International Conference on Macromolecules, Bratislava; 06.09.2016 - 09.09.2016; in: "Programme Book and Book of Abstracts", (2016), ISBN: 978-80-89841-01-1; S. 17.

Photopolymers are widely used in applications such as coatings, biomaterials and 3D-printing. However, the evolution of high shrinkage stress during the reaction and therefore brittle behavior of the resulting polymers are still a drawback. These problems are due to the very inhomogeneous network structure of the radically cured photopolymers [1]. So a strong desire for additives, which act as network regulators, is given.
A common approach for radical polymerization is the use of chain transfer agents (CTAs), which lead to more homogeneous networks, thus tunable mechanical properties, reduced shrinkage stress and high conversion. The most commonly known CTAs are thiols (thiol-ene chemistry) [2], but also very good results are obtained with addition fragmentation chain transfer (AFCT) reagents [3], e.g. β-allyl sulfones [4] and vinyl sulfonate esters [5].
Silanes, which are already well known in polymer chemistry from metal catalyzed crosslinking of polysiloxanes (hydrosilylation), are suggested from Lalevée et al. [6] as CTAs (Figure 1). Tris(trimethylsilyl)silane (TTMSS) was found to be the most effective transfer agent for radical polymerizations.
Based on this publication a closer look at this potential silane-ene chemistry was taken. Therefore, a general synthesis for monosubstituted bis(trimethylsilyl) silanes (e.g. MSiH) was developed. The photoreactivity of MSiH towards various alkenes was evaluated by UV irradiation and following NMR analysis in comparison to TTMSS and a monofunctional thiol (MSH) as reference compounds. Finally, GPC measurements were done with the most promising silane-ene polymers (i.e. silane-acrylate and silane-vinyl ester) to proof the chain transfer activity of MSiH in radical photopolymerization. In addition, this synthetic approach can potentially be used to make multifunctional derivatives for application in polymer networks.

Photopolymerization, Silan-ene Chemistry, Biomaterials, 3D-printing