The pronouncedly low thermal conductivity of polymers in the range of 0.1–0.2 W m⁻¹ K⁻¹ is a limiting factor for their application as an insulating layer in microelectronics that exhibit continuously higher power-to-volume ratios. Two strategies can be applied to increase the thermal conductivity of polymers; that is, compounding with thermally conductive inorganic materials as well as blending with aromatic units arranged by the principle of π-π stacking. In this study, both strategies were investigated and compared on the example of epoxy-amine resins of bisphenol A diglycidyl ether (BADGE) and 1,2,7,8-diepoxyoctane (DEO), respectively. These two diepoxy compounds were cured with mixtures of the diamines isophorone diamine (IPDA) and o-dianisidine (DAN). The epoxy-amine resins were cured without filler and with 5 wt.-% of SiO₂ nanoparticles. Enhanced thermal conductivity in the range of 0.4 W·m⁻¹·K⁻¹ was observed exclusively in DEO-based polymer networks that were cured with DAN (and do not contain SiO₂ fillers). This observation is argued to originate from π-π stacking of the aromatic units of DAN enabled by the higher flexibility of the aliphatic carbon chain of DEO compared with that of BADGE. The enhanced thermal conductivity occurs only at temperatures above the glass-transition point and only if no inorganic fillers, which disrupt the π-π stacking of the aromatic groups, are present. In summary, it can be argued that the bisphenol-free epoxy-amine resin with an epoxy compound derivable from natural resources shows favorably higher thermal conductivity in comparison with the petrol-based bisphenol-based epoxy/amine resins.

Due to the specific vacuum requirements for scanning electron microscopy (SEM), the Raman microscope has to operate in vacuum in a correlative Raman-SEM, which is a type of microscope combination that has recently increased in popularity. This works considers the implications of conducting Raman microscopy under vacuum, as opposed to operating in ambient air, the standard working regime of this technique. We show that the performance of the optics of the Raman microscope are identical in both conditions, but laser beam-sample interactions, such as fluorescent bleaching and beam damage, might be different due to the lack of oxygen in vacuum. The bleaching of the fluorescent background appears to be mostly unaffected by the lack of oxygen, except when very low laser powers are used. Regarding laser-beam damage, organic samples are more sensitive in vacuum than in air, whereas no definite verdict is possible for inorganic samples. These findings have practical implications for the application of correlative Raman-SEM, as low laser powers, or in extreme cases cryo-methods, need to be used for organic samples that appear only moderately beam sensitive under usual ambient air.

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.