Fabio Blaschke1,2, Philipp Marx1,3, Stefan Hirner1,2, Inge Mühlbacher1, Karin Wewerka4, Frank Wiesbrock1. 1. Polymer Competence Center Leoben GmbH, Roseggerstrasse 12, 8700 Leoben, Austria. 2. Institute for Chemistry and Technology of Materials, Graz University of Technology, NAWI Graz, Stremayrgasse 9, 8010 Graz, Austria. 3. Chair of Chemistry of Polymeric Materials, Montanuniversitaet Leoben, Otto-Gloeckel-Str. 2, 8700 Leoben, Austria. 4. Center for Electron Microscopy, Institute for Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria.
Abstract
In the course of this study, the dielectric and physicochemical properties of poly(2-oxazoline) (POx) networks from renewable resources were compared with those of fossil-based polyamide 12 (PA 12) networks. POx was synthesized by the energy-efficient, microwave-assisted copolymerization of 2-oxazoline monomers, which were derived from fatty acids of coconut and castor oil. For the preparation of composites, aluminum nitride nanoparticles n-AlN and microparticles μ-AlN as well as hexagonal boron nitride BN submicroparticles were used. Additionally, 0, 15, or 30 wt.% of a spiroorthoester (SOE) were added as an expanding monomer aiming to reduce the formation of shrinkage-related defects. For the crosslinking of the polymers and the SOE as well as the double ring-opening reaction of the SOE, a thermally triggered dual-cure system was developed. The fully-cured blends and composites containing SOEs exhibited lower densities than their fully-cured SOE-free analogues, which was indicative of a lower extent of shrinkage (or even volumetric expansion) during the curing reaction, which is referred to as relative expansion RE. The RE amounted to values in the range of 0.46 to 2.48 for PA 12-based samples and 1.39 to 7.50 vol.% for POx-based samples. At 40 Hz, the "green" POx networks show low loss factors, which are competitive to those of the fossil-based PA 12.
In the course of this study, the dielectric and physicochemical properties of n class="Chemical">poly(2-oxazoline)n> (POx) networks from renewable resources were compared with those of fossil-based polyamide 12 (PA 12) networks. POx was synthesized by the energy-efficient, microwave-assisted copolymerization of 2-oxazoline monomers, which were derived from fatty acids of coconut and castor oil. For the preparation of composites, aluminum nitride nanoparticles n-AlN and microparticles μ-AlN as well as hexagonalboron nitride BN submicroparticles were used. Additionally, 0, 15, or 30 wt.% of a spiroorthoester (SOE) were added as an expanding monomer aiming to reduce the formation of shrinkage-related defects. For the crosslinking of the polymers and the SOE as well as the double ring-opening reaction of the SOE, a thermally triggered dual-cure system was developed. The fully-cured blends and composites containing SOEs exhibited lower densities than their fully-cured SOE-free analogues, which was indicative of a lower extent of shrinkage (or even volumetric expansion) during the curing reaction, which is referred to as relative expansion RE. The RE amounted to values in the range of 0.46 to 2.48 for PA 12-based samples and 1.39 to 7.50 vol.% for POx-based samples. At 40 Hz, the "green" POx networks show low loss factors, which are competitive to those of the fossil-based PA 12.