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Marburg an der Lahn, Germany

Schraub M.,University of Marburg | Gray H.,Imperial College London | Hampp N.,University of Marburg | Hampp N.,Materials Science Center Marburg
Macromolecules | Year: 2011

Stilbene is known to undergo two different reactions upon photochemical excitation. The first is an E/Z isomerization and the second is a [2 + 2]-cycloaddition of two stilbene molecules. Because both reactions occur in parallel their use is limited. Here we report on photorefractive polymers with a methacrylate backbone and covalently attached 4-hydroxy-(E)-stilbene or 3,5-dimethoxy-4-hydroxy-(E)-stilbene units in the side chain which show [2 + 2]-cycloaddition only. Both polymers, poly(4-methacryloyloxy-(E)-stilbene) (PMAES) and poly(4-methacryloyloxy-3,5-dimethoxy-(E)-stilbene) (PMADMES), show very high initial refractive indices of 1.6533 for PMAES and 1.6288 for PMADMES. The photochemical reaction upon laser irradiation with 355 nm was monitored by UV/vis, fluorescence, and IR spectroscopy. The light-induced changes of the refractive index at 633 nm measured by surface plasmon resonance (SPR) were found to be Δn > 0.05 for PMAES and Δn > 0.04 for PMADMES. The sensitivity of PMADMES is enhanced compared to PMAES due to the electron donating groups (EDG) as the direct comparison of both polymers shows. Both polymers are useful for optical devices because they do not show any absorption in the visible range and are noncrystalline as determined by wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC). © 2011 American Chemical Society. Source


Schraub M.,University of Marburg | Kim H.-C.,University of Marburg | Hampp N.,University of Marburg | Hampp N.,Materials Science Center Marburg
European Polymer Journal | Year: 2014

A novel photorefractive polymer has been developed where 3-phenyl-coumarin (3PC) is attached via alkyl spacers to a methacrylate backbone. The 3PC is a fusion of the structural motives of coumarin and stilbene. In 3PC the E/Z-isomerization, known from stilbenes, is blocked and a more extended conjugated π-electron system than in coumarin is obtained. A methacrylate based polymeric material comprising 3PC in the side chain has been synthesized and its photorefractive properties have been studied. The initial refractive index is n633o = 1.613 and the maximal light-induced change of the refractive index was found to be Δn633 = -0.045 in spin-coated thin films as well as in bulk material. The glass transition temperature of about 37 C and the high lightfastness of the polymer make it a candidate material for intraocular lenses with photo-tunable refractive index properties. © 2013 Elsevier Ltd. All rights reserved. Source


Schraub M.,University of Marburg | Soll S.,Max Planck Institute of Colloids and Interfaces | Hampp N.,University of Marburg | Hampp N.,Materials Science Center Marburg
European Polymer Journal | Year: 2013

In the past decades the development of photorefractive devices evolved rapidly as can be seen by the increasing number of publications and numerous applications. There is still need of innovative materials which are suitable for a broad range of applications through tailored properties. We present photorefractive linear and crosslinked polysiloxanes with refractive indices of up to n = 1.603 which may be tuned in their refractive index in a range of up to Δn = 0.04 photochemically. The polysiloxanes, more commonly named silicones, have side chains containing coumarin which are attached to the polymer backbone via different spacers ranging in length from 3 to 9 methyl groups. The coumarins undergo wavelength-dependent photodimerization and photocleavage in the polymer which cause the desired refractive index changes. The polysiloxanes have low glass transition temperatures ranging from -2 C to 35 C and show a high thermal stability (T5% > 410 C). These properties make these materials promising candidates for the manufacture of photo tunable polymers, e.g. for the use as optical data storage materials, alignment of liquid crystals, and photorefractive intraocular lenses. © 2013 Elsevier B.V. All rights reserved. Source

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