Tailoring Epoxy Resin Foams by Pre-Curing with Neat Amine Hardeners and Its Derived Carbamates.

The use of amine-based carbamates with their dual function, acting as amine curing agents and CO2 blowing agents after their decomposition without by-products, are promising for ecofriendly epoxy foams as high-performance materials. However, controlling cell morphology requires a proper adjustment of the viscosity at the foaming step. The viscosity is altered not only by blending neat amine and its derived carbamate at a fixed pre-curing time, but also by changing the pre-curing time at a fixed blend ratio. Within this study, diglycidylether of bisphenol A (DGEBA) epoxy resin is mixed with different blend ratios of isophorone diamine (IPDA) and its derived carbamate (B-IPDA). The systems are characterized by DSC and rheology experiments to identify the pre-curing effects on the derived epoxy foams. Epoxy foams at a blend ratio of 30/70w IPDA/B-IPDA showed the best foam morphology and an optimum Tg compared to other blend ratios. Furthermore, it was found that both pre-curing times, 2 h and 3 h, for the 30/70w IPDA/B-IPDA system reveal a more homogeneous cell structure. The study proves that the blending of neat amine and carbamate is beneficial for the foaming performance of carbamate systems.

Simple and High Yield Synthesis of Metal-Polymer Nanocomposites: The Role of Theta-Centrifugation as an Essential Purification Step.

Nanocomposites are an important materials class, which strives to foster synergistic effects from the intimate mixture of two vastly different materials. Inorganic nanoparticles decorated with polymer ligands, for instance, aim to combine the processing flexibility of polymers with the mechanical robustness of solid state materials. The fabrication and purification of such composite nanoparticles, however, still presents a synthetic challenge. Here, we present a simple synthesis of silver polystyrene nanocomposites with a controllable interparticle distance. The interparticle distance can be well-controlled with a few nanometer precision using polystyrene ligands with various molecular weights. The nanoparticle and polymer ligand synthesis yield both materials on gram scales. Consequently, the polymer nanocomposites can also be fabricated in such large amounts. Most importantly, we introduce Θ-centrifugation as a purification method, which is capable of purifying large nanocomposite batches in a reproducible manner. We employ a range of characterization methods to prove the successful purification procedure, such as transmission electron microscopy, thermogravimetric analysis, and dynamic light scattering. Our contribution will be of high interest for many groups working on nanocomposite materials, where the sample purification has been a challenge up to now.