Trialkoxysilane grafting onto nanoparticles for the preparation of clear coat polyacrylate systems with excellent scratch performance

Transparent reinforced polyacrylates were prepared using nanosized filler particles with radiation-curable acrylates. To improve embedding of the nanofillers within the acrylate matrix the filler surface was chemically modified. This modification of the silica and alumina nanoparticles was accomplished by trimethoxysilanes having methacryloxypropyl (MEMO), vinyl (VTMO), and n-propyl (PTMO) functionalities. Due to acid catalyzed condensation of organosilanes a polysiloxane shell was formed around the nanoparticles. This shell is bonded to OH groups on the filler surface. The appearance of covalent Si-O-Si-R bonds was clearly shown by multinuclear MAS NMR. MALDI-TOF mass spectroscopy revealed the formation of polysiloxane oligomers with different degrees of condensation. In the work presented, an acrylate-nanocomposite formulation contains up to 35 wt.% nanosized silica covered with polysiloxanes. For MEMO modification, surface-anchored methacryl groups can copolymerize with network acrylates. But also PTMO-modified composite materials exhibit markedly improved properties as compared to the neat acrylate polymer; e.g., an increased modulus and heat resistance, improved scratch and abrasion resistance. This makes polyacrylate nanocomposites a very promising new coating technology for many far reaching technical applications. (C) 2003 Elsevier B.V. All rights reserved.