Helmut Langguth

Preparation of scratch and abrasion resistant polymeric nanocomposites by monomer grafting onto nanoparticles, 1 FTIR and multi‐nuclear NMR spectroscopy to the characterization of methacryl grafting

Nano-sized silica and alumina particles were used as fillers for polymer reinforcement and scratch resistant coatings. For favorable embedding within the polyacrylate matrix the surface of the fillers was chemically modified by reaction with methacroyloxy (propyl)-trimethoxysilane. The formation of covalent Si(Al)-O-Si-C bonds between functional groups from silane and OH groups on silica and alumina was demonstrated by means of FTIR and MAS NMR spectroscopy. The reactivity of the various surface silanols towards the coupling agent and the yield of surface Si-O-Si bonds were estimated by 29 Si CP MAS NMR data.

Preparation of Scratch and Abrasion Resistant Polymeric Nanocomposites by Monomer Grafting onto Nanoparticles, 3. Effect of Filler Particles and Grafting Agents

After modification with different trialkoxysilanes, nano-sized silica and alumina particles were used as fillers in transparent UV/EB curable acrylates for polymer reinforcement, particularly to attain scratch and abrasion resistant coatings. The acid catalyzed condensation of the organosilanes forms a polysiloxane shell which covers the nanoparticle like a nanocapsule. CP MAS NMR spectroscopy and MALDI-TOF mass spectrometry proved to be useful for the characterization of the polysiloxane structures. Grafter oligomers with more than 20 monomeric units were observed. Nanoparticles modified by methacroyloxy(propyl)trimethoxysilane and vinyltri-methoxysilane can copolymerize with acrylates. Compared with the pure polymers, these crosslinked polyacrylate nanocomposites, containing up to 35 wt.-% silica, exhibit markedly improved surface mechanical properties. Promising scratch and abrasion resistance of radiation-cured nanocomposite materials were also obtained by propyltrimethoxysilane grafting which results in an organo-philation of pyrogenic silica. Both colloidal and pyrogenic nano-sized silica nanopowders were used as fillers in polyacrylate films. The concentration of colloidal SiO 2 in commercial acrylate formulations amounts up to 50 wt.-%, whereas pyrogenic silica, notwhithstanding their surface modification by silanes, results in a thickening effect which limits its content to about 35 wt.-%. Never-theless, a comparison showed a distinct improvement in the surface mechanical properties such as haze and diamond microscratch hardness for surface-modified pyrogenic silica.

Preparation of scratch and abrasion resistant polymeric nanocomposites by monomer grafting onto nanoparticles, 2 Characterization of radiation‐cured polymeric nanocomposites

By in situ grafting methacroyloxy functionalized-silanes on commercial nanoglobular silica polymerization-active silico-organic nanoparticles were prepared. In radiation (UV, EB) induced polymerization reactions these modified nanoparticles form covalent crosslinks to acrylate substrates, thus efficiently modifying their viscoelastic properties. The transparent nanopowder composites can be used as scratch resistants coatings. The composite films show excellent adhesion on PC and PVC and good abrasion resistance after the Taber abraser test with haze values of about 6% after 500 cycles.

The effect of temperature on the induction period in the photoinitiated polymerization of tripropylene glycol diacrylate

Abstract The effect of temperature on the kinetics of the photopolymerization of tripropylene glycol diacrylate was studied by real-time FTIR–attenuated total reflection (ATR) spectroscopy. The temperature behaviour of the polymerization rate was found to be dependent on the photoinitiator used. The induction period strongly decreases with increasing temperature. It was shown by quantitative determination of the oxygen concentration that the decay of the induction period is solely due to the decreasing solubility of oxygen in the acrylate.