Thermische zersetzung von benzpinakol und benzpinakolbis(trimethylsilyl)ethern in UP‐harzen

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Abstract
During thermal cleavage of benzpinacol (1) in unsaturated polyester resins only 20–40% of the produced semibenzpinacol radicals (2) react via hydrogen transfer. The other radicals disproportionate into benzophenone and benzhydrol or add directly to the double bonds of the unsaturated polyester resin or to the growing polymer radicals. As during thermal cleavage of benzpinacol bis(trimethylsilyl) ether (5) in unsaturated polyester resins only up to 10% of the diphenyltrimethylsiloxymethyl radicals (6) undergo secondary fragmentation, we suppose that the curing of unsaturated polyester resins with 5 is initiated mainly by the relatively stable primary radicals 6. The different activity of the two compounds 1 and 5 in initiating radical polymerisation is explained by different mechanisms in the initiation process.