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G. Peer, A. Eibel, C. Gorsche, Y. Catel, G. Gescheidt, N. Moszner, R. Liska:
"Regulation of Methacrylate Networks via Ester-Activated Vinyl Ethers as ChainTransfer Agents";
Poster: RadTech USA 2019, Monterey - CA, USA; 15.09.2019 - 18.09.2019.

Multifunctional methacrylates show high reactivity in radical polymerization but exhibit shrinkage stress during polymerization and tend to form highly cross-linked networks, which yield brittle materials. In order to regulate the network formation and to increase the toughness, chain transfer agents (CTA) are used as additives. Thiol-ene chemistry presents a widely researched CTA-technology and exhibits high reactivity together with increased toughness in methacrylate systems.1 Apart from thiol-ene systems, addition fragmentation chain transfer (AFCT) agents represent a viable alternative and are known since the 1980s.2 Typically, AFCT agents contain an activating group adjacent to a carbon-carbon double bond (e.g. ester moiety), a particular center atom (e.g. carbon atom) and a leaving group (e.g. tosyl moiety). Moad et al. published an extensive review on AFCT-agents and their regulation efficiency in numerous monomers.3 Recently, the substitution of carbon (β-allyl sulfone) as a center atom to oxygen (vinyl sulfonate ester) was described and the irreversible ketone formation after fragmentation of the latter leads to a significant increase in reactivity.4
The same principle was used to alter a methyl methacrylate dimer to an activated vinyl ether (VE). VE have been described as potent AFCT agents in radical polymerization but are unexamined in network formation via photopolymerization. While a challenging synthesis and considerable acid sensitivity are generally attributed to vinyl ethers, we present a sterically hindered vinyl ether with enhanced acid stability to demonstrate the significant increase in reactivity when employing an irreversible AFCT system.5 An efficient polymerization regulation was confirmed in a monofunctional system and evaluation in a difunctional methacrylate system revealed high reactivity, increased toughness and lower shrinkage stress. Therefore, sterically hindered activated vinyl ethers present an expedient tool to tailor the (thermo)mechanical properties of photopolymers and resulting materials.

Multifunctional methacrylates, radical polymerization, shrinkage stress, highly cross-linked networks, increase the toughness, chain transfer agents, Thiol-ene chemistry