Silane reduction of onium salts

Abstract

Novel redox initiators for cationic polymerizations were developed consisting of an onium salt together with a Si-H functional silane or siloxane. The reduction of the onium salt by the silane is catalyzed by noble metal complexes or certain transition metal compounds and takes place spontaneously at room temperature. The redox reaction of the onium salt with the silane results in the liberation of a strong Brønsted acid that can be subsequently used to initiate cationic polymerizations. Typical onium salts that have been employed in these redox initiator systems are diaryliodonium salts, triarylsulfonium salts and S,S-dialkyl-Sphenacylsulfonium salts. Studies of the effects of variations in the structures of the onium salt, the silane and the type of noble metal catalyst were carried out. In principle, the redox initiator systems are applicable to all types of cationically polymerizable monomers and oligomers, including the ring-opening polymerizations of such heterocyclic monomers as epoxides and oxetanes and, in addition, the polymerization of vinyl monomers such as vinyl ethers, N-vinylcarbazole and styrenic monomers. The use of these novel initiator systems for carrying out commercially attractive crosslinking polymerizations for coatings, composites and encapsulations is discussed.

In Situ Synthesis and Characterization of Silver/Polymer Nanocomposites by Thermal Cationic Polymerization Processes at Room Temperature: Initiating Systems Based on Organosilanes and Starch Nanocrystals

“…The reaction is too slow with α-PO to use a similar procedure. It has been shown in refs and that the increase of the temperature is directly related to the monomer conversion. The present setup used here being not adiabatic, the relationship between the conversion and the temperature will be valid only for the first steps of the polymerization process.…”

“…Among various initiation systems for CP of epoxides, redox couples are interesting , as exemplified by a recent new tricomponent combination , based on onium salt and organosilane (R 3 SiH) as reducing agent and platinum, palladium, or rhodium as metal catalyst. On the other side, we recently developed a two-component redox system based on a tris­(trimethylsilyl)­silane TTMSS/silver salt combination which allows one to efficiently initiate the ROP of epoxides at RT and incorporate metal M(0) nanoparticles in the film …”

Recent Advances on Visible Light Metal-Based Photocatalysts for Polymerization under Low Light Intensity

“…The first examples of Pt-based photocatalysts for photopolymerization were reported in 2012 [33]. However, it has to be mentioned that Pt complexes were previously used in redox-initiating systems of polymerization [34,35]. Here again, the two Pt complexes Pt-1 and Pt-2 proved to be efficient photocatalysts for the CP of EPOX in three-component photoinitiating systems (see Figure 4).…”