One important challenge in the design of polymer-based dielectrics is the volumetric shrinkage during the curing reaction, which results in mechanical stresses, microcracks, cavities and delamination. Furthermore, due to the constantly increasing power densities in microelectronics and high-voltage technology, the increased operating temperatures must also be considered for the development of polymer-based dielectrics, which correspondingly must exhibit continuously increased thermal conductivity. The aim of this dissertation was the preparation of resins and composites with increased thermal conductivity, which show reduced shrinkage or even expansion during the curing reaction. In a first step, an allyl-functionalized spiroorthoester SOE was synthesized as an expanding monomer, which can be covalently attached into various polymer networks via the allyl group. The SOE was used as an additive to reduce the shrinkage in a light-curable thiol-ene resin of Bisphenol-A diallyl ether and a trifunctional thiol hardener. For this purpose, a dual-cure system was developed, which enables both, the radical network formation and the cationic ring-opening polymerization of the SOE with volumetric expansion. By varying the SOE content between 0 and 30 wt.-%, expansions between -3.07 and +1.70 vol.-% are achieved during curing. The SOE was also used to reduce the shrinkage during the curing of a high-k dielectric based on polyethers. Tri(ethylene glycol) divinyl ether was chosen as oligomer, which was crosslinked by the developed dual-cure system comprising the photochemical thiol-ene click reaction and (ring-opening) copolymerization with the SOE. The shrinkage could be reduced by 39% by adding 50 wt.-% of SOE. The permittivity of the polymer networks reaches values of up to 10,000. Using digital light processing, structures with a resolution of 50 micrometer could be printed. In addition, the SOE was used to reduce the shrinkage during the crosslinking of Polyamide 12 and a copoly(2-oxazoline), the latter of which was synthesized from renewable raw materials. In the thermally initiated dual-cure reaction, expansion between +0.46 and +2.48 vol.-% (Polyamide 12) and +1.54 and +7.96 vol.-% [copoly(2-oxazoline)] could be achieved. The thermal conductivity could be increased by adding different filler combinations of AlN and BN particles. As the SOE content increases, the permittivity of the materials increases. This can be explained by the increase in the free volume of the polymer networks due to the expansion. In addition to the shrinkage, the dielectric properties of epoxy-amine resin-based nanocomposites was investigated. Silica, silica-TMS, alumina, alumina-TMS and BN were used as fillers; the trimethyl silylation of the corresponding TMS particles was achieved by reaction with hexamethyl disilazane. The dielectric properties do not primarily depend on the amount of absorbed water, but essentially on the OH group content of the nanoparticles and the interfacial polarization influenced by this. In another study, the heat conduction in inhomogeneous gradient composites was investigated. An epoxy-amine resin with alumina nanoparticles and alumina microparticles as fillers was used to prepare gradient composites. Light-flash analysis measurements of the individual layers of a cut gradient composite showed that the thermal conductivity along the height of the material varies between 0.25 and 0.45 W / (m K). Using guarded heat flow meter measurements of an uncut composite, only the lowest thermal conductivity occurring in the material could be determined. In order to analyze the heat conduction in gradient composites in detail, a simulation model was developed on the basis of the experimental data.