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Latent, thermally or UV-triggerable Catalysts for Step- and Chain Growth Polymerization (PUR Synthesis, ROMP,…)

A series of latent, thermally and/or UV- triggerable catalysts based on CO2-protected N-heterocyclic carbene (NHC), NHC-Sn and NHC-Ru complexes for step- and chain-growth polymerization have been synthesized. The CO2-protected NHC and NHC-Sn complexes show very good thermal latency in the presence of difunctional alcohol (polyol) and a difunctional isocyanate and can only be activated at elevated temperatures. Particularly the CO2-protected pre-catalysts showed not only the excellent activity and latency comparing with the existing systems; they also circumvent the use of toxic heavy metals such as HgII.

Complementary, the ring-opening metathesis polymerization (ROMP) by novel cationic RuII-NHC complexes in the presence of various norborn-2-ene-substituted monomers can only be activated by UV irradiation. These initiators are of particular interest in technical applications of ROMP, they allow for premixing of a monomer/pre-catalyst mixture and its storage over long periods of time at elevated temperatures. Most importantly, these initiators allow for shaping and profiling of such mixtures prior to polymerization ("curing").

Current research focuses on the development of new UV or thermally latent pre-catalysts for other polymerizations.

Figure 1. Reactivity and latent behavior of catalysts 1-4 in comparison to A and B in the polyaddition reaction of the polyol with HDI-cyclotrimer: Structure of catalysts 1-4, A, B and of the monomers used (middle); Structure of precatalyst 5, 6 and monomers 7-12 (right)