A Comprehensive Study of Polyurethane Potting Compounds Doped with Magnesium Oxide Nanoparticles

Recently, polyurethanes (PURs) have become a very promising group of materials with considerable utilization and innovation potential. This work presents a comprehensive analysis of the changes in material properties important for PUR applications in the electrical industry due to the incorporation of magnesium oxide (MgO) nanoparticles at different weight ratios. From the results of the investigations carried out, it is evident that the incorporation of MgO improves the volume (by up to +0.5 order of magnitude) and surface (+1 order of magnitude) resistivities, reduces the dielectric losses at higher temperatures (-62%), improves the thermal stability of the material, and slows the decomposition reaction of polyurethane at specific temperatures (+30 °C). In contrast, the incorporation of MgO results in a slight decrease in the dielectric strength (-15%) and a significant decrease in the mechanical strength (-37%).

Structure–properties relationship of the polyurethanes that contain Schiff base in the main chain

This article studies the diversification of useful properties of polyurethane (PU) structures by the inclusion of new components. PUs containing a Schiff base in the main chain were synthesized by using N, N′-bis(salicylidene)-1,3-propanediamine as a chain extender. Novel Schiff base PUs were synthesized via a two-step polymerization starting from a Schiff base derivative diol chain extender with different molar ratios or by cross-linking with various natural raw materials. The sought after structures was confirmed by Fourier transform infrared spectra that showed the disappearance of the signals of both the hydroxyl and isocyanate groups. The thermal properties of these PUs were investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The initial degradation temperatures of the obtained PUs were found to be in the range of 300–350°C. Based on the results from DMA, the rigid structure of the Schiff base from the backbone of the PUs presented a higher storage modulus, results which may be connected to the physical cross-linking process of the macromolecules. Their optical properties were determined by fluorescence spectroscopy. The incorporation of Schiff base structures into the main PU chain generates new PU structures with improved thermomechanical properties, which includes possible bioactive Schiff base moieties, widening the range of practical applications for such polymers.

Mesoscopic simulations of hydrophilic cross-linked polycarbonate polyurethane networks: structure and morphology

Polyurethane (PU) cross-linked networks are frequently used in biomedical and marine applications, e.g., as hydrophilic polymer coatings with antifouling or low-friction properties and have been reported to exhibit characteristic phase separation between soft and hard segments. Understanding this phase-separation behavior is critical to design novel hydrophilic polymer coatings. However, most of the studies on the structure and morphology of cross-linked coatings are experimental, which only assess the phase separation via indirect methods. Herein we present a mesoscopic simulation study of the network characteristics of model hydrophilic polymer networks, consisting of PU with and without methyl-polyethylene glycol (mPEG) dangling chains. The systems are analyzed using a number of tools, such as the radial distribution function, the cross-link point density distribution and the Voronoi volume distribution (of the cross-linking points). The combined results show that the cross-linked networks without dangling chains are rather homogeneous but contain a small amount of clustering of cross-linker molecules. A clear phase separation is observed when introducing the dangling chains. In spite of that, the amount of cross-linker molecules connected to dangling chains only, i.e., not connected to the main network, is relatively small, leading to about 3 wt% extractables. Thus, these cross-linked polymers consist of a phase-separated, yet highly connected network. This study provides valuable guidelines towards new self-healing hydrophilic coatings based on the molecular design of cross-linked networks in direct contact with water or aqueous fluids, e.g., as anti-fouling self-repairing coatings for marine applications.

Synthesis and characterization of novel linear and cross-linked polyurethane urea elastomers with 2,3-diaminopyridine in the main chain

Novel polyurethane urea containing pyridine moieties in their main chains have been prepared by a two-step solution polymerization procedure. These polyurethane urea elastomers were synthesized by chain-extending isocyanate end-capped prepolymers with 2,3-diaminoyridine and different cross-linkers. The isocyanate-terminated prepolymers were obtained from poly(tetramethylene oxide) glycol of molecular weight 1400 (Terathane 1400) and 1,6-hexamethylene diisocyanate. Including pyridine derivatives into the structural compositions leads to a change in properties that were investigated using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), mechanical measurements and contact angle and fluorescence analysis. The results show that intermolecular hydrogen bonds have formed between pyridine groups and urethane or urea groups, affecting all the obtained properties.

Effect of resorcinol-based chain extenders chemical structure on the enhanced properties of polyurethane elastomers

Two series of polyurethane elastomers with resorcinol derivatives in the polymer backbone were synthesized by chain extending isocyanate end-capped prepolymers with resorcinol, 2,4-dihydroxybenzaldehyde or 1-(2,4-dihydroxyphenyl)-hexanone-(1). Chain extenders are differentiated from each other by the structure of the side chain attached to the resorcinol rings. Isocyanate-terminated prepolymers were obtained from poly(1,4-butylene adipate) diol and 4,4′-diphenylmethane diisocyanate. These polyurethane elastomers were characterized using Fourier transform infrared spectroscopy, thermo-gravimetric analysis, differential scanning calorimetry, and mechanical measurements. The effects of the chemical structure of resorcinol-derivative chain extenders on the properties of polyurethane elastomers were investigated. A significant increase in maximum stress–strain properties and in thermal stability was observed for the samples with free carbonyl in the side chain of the resorcinol ring. All the polymers showed 5% weight losses above 300 °C and glass transition temperature values in the range of −39 and −23 °C. The aim was to enhance the mechanical properties and thermal behavior by varying the chemical structure of the resorcinol moieties from the hard segment domain, without transform phenolic OH groups in aliphatic OH groups.