Summary: UV curable acrylate formulations with a high content of fumed, nano‐sized silica were prepared to improve their application for abrasion and scratch resistant top coats. Grafting of trialkoxysilanes onto the surface of nanoparticles facilitated their embedding in the formulation and alleviated the effect of undesired increase in viscosity and dilatancy. Modified nanoparticles were obtained from several organosilanes and characterized by a multitechnique approach. To avoid problems during redispersion, in situ modification of nano‐sized silica was performed using the liquid acrylate formulation as a diluting and deagglomerating agent. These nanocomposite materials exhibit markedly improved properties as compared to neat acrylate coatings, e.g. heat, scratch, and abrasion resistance. However, a much better abrasion resistance was obtained for coatings containing both silica nanoparticles and corundum microparticles. By using various grades of corundum, a synergetic effect of nano/micro hybrid composite materials has been studied for parquet and flooring applications.Pictures of neat polyacrylate coating (on the left) and nano/micro hybrid composite material (18 wt.‐% silica +15 wt.‐% corundum) on parquet substrate after Taber Abraser Test.imagePictures of neat polyacrylate coating (on the left) and nano/micro hybrid composite material (18 wt.‐% silica +15 wt.‐% corundum) on parquet substrate after Taber Abraser Test.
The initiation mechanism of the VUV-induced conversion of polyorganosilazanes into methyl-Si-O-Si networks was studied by means of model disilazane compounds. A combined experimental approach was chosen to determine the primary radicals and their properties (lifetimes, spectra) as well as the major final products. It was verified that both Si-N and Si-CH(3) cleavage occur in the condensed phase, the former with higher yield. The lifetime of the primary Si- and N-centred radicals in de-oxygenated n-hexane solution is less than =10 mus. N-centred radicals transform into amines by H abstraction, the availability of weakly bonded H as in the case of tetramethyldisilazane accelerates the reaction considerably. In rigid matrix (frozen solutions) CH(3), silyl radicals and methylene radicals CH(2)R are trapped. In the presence of oxygen, peroxyl radicals are formed and serve as precursors of the subsequent oxidative conversion. Product analysis by GC-MS reveals linear R-(Si-O)(n)- chains rather than branched compounds as the initial products of the oxidative conversion of tetramethyldisilazane. It was shown that reactive silylene intermediates do not play a role in the conversion process. Quantum chemical calculations assist in the interpretation.
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