Dual/Bi-Stage Curing of Nanocomposites from Renewable Resources upon Volumetric Expansion

Nowadays, polymers used in technical applications are still obtained from petrochemicals, despite the more critical reviews from society. In this work, novel nanodielectrics based on renewable resources were developed. For this purpose, poly(2-oxazoline)s (POx), which can be referred to as pseudo-polyamides, were synthesized from renewable resources and compared with commercially available Nylon 12, which is derived from petrochemicals. The monomers 2-nonyl-2-oxazoline and 2-dec-9′-enyl-2-oxazoline were synthesized from coconut oil and castor oil in solvent-free syntheses according to the Henkel Patent; the corresponding copoly(2-oxazoline)s were synthesized in an energy-efficient fashion in microwave reactors under autoclave conditions. Both types of polyamides (two variations: POx and Nylon 12) were filled with inorganic nanoparticles (four variations: no filler, submicro-scaled BN, nano- and micro-scaled AlN as well as a mixture of nano- and micro-scaled AlN and submicro-scaled BN) and/or expanding monomers, namely spiroorthoesters (three variations: 0, 15, and 30 wt.-%), yielding a 2 × 4 × 3 = 24-membered material library. All polymers were crosslinked according to a newly developed thermally-initiated dual/bi-stage curing system. Intense physicochemical and dielectric characterization revealed that the relative volume expansion was in the range of 0.46 to 2.48 vol.-% for the Nylon 12 samples and in the range of 1.39 to 7.69 vol.-% for the POx samples. Hence, the formation micro-cracks or micro-voids during curing is significantly reduced. The dielectric measurements show competitive dielectric behavior of the “green” POx samples in comparison with the fossil-based Nylon 12 samples at a frequency of 40 Hz.