[Zurück]

N. Klikovits, P. Knaack, D. Bomze, I. Krossing, R. Liska:
"Novel photoacid generator for cationic photopolymerization";
Vortrag: Danube Vltava Sava Polymer Meeting 2017, Wien; 05.09.2017 - 08.09.2017; in: "Danube Vltava Sava Polymer Meeting 2017", Book of Abstracts.com, (2017), ISBN: 978-3-9504017-6-9; S. OP-87.

Cationic photopolymerization is a powerful method for light-induced curing of heterocyclic and vinyl monomers such as epoxides, oxetanes and vinyl ethers. The main benefits of cationic UV-curing, namely high reaction rates, insensitivity towards oxygen and post-curing in the absence of light, make it highly useful for the production of coatings, adhesives and inks with low energy consumption and high efficiency. Especially epoxides provide special product features, such as excellent adhesion, mechanical strength and chemical resistance, which cannot be reached by predominant free radical photopolymerization and corresponding monomers.
Still the lack of suitable and efficient photoinitiators limits the potential of cationic UV-curing. The acid-induced polymerization is started by photoacid generators (PAGs), which liberate protons and carbocations upon UV-light irradiation. Only little progress has been achieved since the development of onium salt PAGs in the 1970s, which demonstrated the efficient photodecomposition of diaryliodonium and triarylsulfonium cations.1, 2 Low nucleophilic, perfluorinated anions as BF4-, PF6-, AsF6-, SbF6- and B(ArF)4- have been used as acid forming components in state-of-the-art PAGs, as low nucleophilicity suppresses termination processes and enhances reactions rates.3, 4 However, the major problems of these anions are described by low hydrolysis stability, severe heavy metal toxicity or difficult synthesis procedures, respectively.
We present a novel class of cationic photoinitiators by introducing tetrakis(perfluoro-t-butyloxy)aluminate as acid-forming anion for onium salt PAGs. This weakly coordinating anion (WCA) is characterized by its outstanding non-nucleophilicity, inherent stability, absence of heavy metals, as well as straight-forward and up-scalable synthesis procedures.5, 6 Following the facile preparation of the diphenyliodonium and triarylsulfonium salt of the named WCA, photo DSC studies revealed the superior reactivity in different cationically polymerizable monomers. Their beneficial properties for cationic photopolymerization were investigated and enable the use in a broad spectrum of UV-curing applications.

Cationic photopolymerization, production of coatings, adhesives and inks with low energy consumption and high efficiency, novel class of cationic photoinitiators