Preparation of Scratch- and Abrasion-Resistant Polymeric Nanocomposites by Monomer Grafting onto Nanoparticles, 4

• Published in: Macromolecular chemistry and physics 2003-03, Vol.204 (3), p.375-383
• Main Authors: Bauer, Frank, Sauerland, Volker, Ernst, Horst, Gläsel, Hans-Jürgen, Naumov, Sergej, Mehnert, Reiner
• Format: Article
• Language: English
• Subjects: coatings; fillers; MALDI; nanocomposites; polysiloxanes
• ISSN: 1022-1352; 1521-3935
• DOI: 10.1002/macp.200390003

To obtain transparent, scratch‐ and abrasion‐resistant coating materials a high content of nanosized silica and alumina filler was embedded in radiation‐curable acrylate formulations by acid catalyzed silylation using trialkoxysilanes. 29Si magic angle spinning (MAS) NMR spectroscopy and matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐TOF MS) were used to elucidate the structure of the surface‐grafted methacryloxypropyl‐, vinyl‐, and n‐propyltrimethoxysilane. 29Si MAS NMR measurements revealed a predominance of T2 and T3 structures of silicon atoms, i.e., silane oligomers have been formed by an extensive loss of water. For methacryloxypropyltrimethoxysilane, the proportion of the highly condensed T3 silicon atoms was estimated to be 75%. In accordance with these NMR findings, MALDI‐TOF MS showed highly condensed oligomeric siloxanes of more than 20 monomeric silane units. The degree of silane condensation is higher on alumina than on silica, irrespective to the addition of maleic acid as catalyst. Moreover, completely condensed silsesquioxanes, e.g., octamers, decamers, and dodecamers, were detected. Based on the observed MS pattern, a ladder‐like arrangement of two linked siloxane chains forming connected eight‐membered rings is proposed, which is similar for all of the condensed organosilanes under study. The grafted polysiloxanes lead to an organophilation of inorganic nanofillers and improve their dispersibility in acrylate suspensions. Proposed ladder‐like arrangement of the T3 structure of silicon atoms in polysiloxanes grafted on the silica surface.