Tough combinatorial poly(urethane-isocyanurate) polymer networks and hydrogels synthesized by the trimerization of mixtures of NCO-prepolymers

Dynamic response of a simply supported liquid-crystal elastomer beam under moving illumination

Optically responsive liquid crystal elastomer (LCE) devices have thriving potential to flourish in soft robots and microdrives, owing to their advantages of remote controllability, structural simplicity, and no power supply. In terms of illumination-driven modes, most research has focused on the dynamic response of LCE devices under continuous and periodic illumination, while the theoretical study of the dynamic response under moving illumination is limited. In this paper, based on the coupling of LCE and mechanical deformation under moving illumination, the dynamic model of a LCE simply supported beam is built to investigate its dynamic response under moving illumination. The analytical solution of the dynamic response of the LCE beam under moving illumination is derived through the modal superposition method and the Duhamel integration, and the solution is programed and analyzed with matlab software. By numerical calculations, the influence of the internal and driving parameters of the structure on the dynamic response of the LCE simply supported beam can be analyzed. The results show that when the moving speed of illumination reaches the first-order critical frequency, the maximum amplitude of the dynamic response at the beam mid-span will reach a peak. Meanwhile, the dynamic response of beam can be improved by increasing the illumination width, increasing the light intensity, increasing the shrinkage coefficient, and reducing the damping coefficient. This work provides theoretical guidance for applying the dynamic response of LCE devices under moving illumination in soft robots, microactuators, energy harvesters, sensors, etc.

Current State and Perspectives of Simulation and Modeling of Aliphatic Isocyanates and Polyisocyanates

Aliphatic isocyanates and polyisocyanates are central molecules in the fabrication of polyurethanes, coatings, and adhesives and, due to their excellent mechanical and stability properties, are continuously investigated in advanced applications; however, despite the growing interest in isocyanate-based systems, atomistic simulations on them have been limited by the lack of accurate parametrizations for these molecular species. In this review, we will first provide an overview of current research on isocyanate systems to highlight their most promising applications, especially in fields far from their typical usage, and to justify the need for further modeling works. Next, we will discuss the state of their modeling, from first-principle studies to atomistic molecular dynamics simulations and coarse-grained approaches, highlighting the recent advances in atomistic modeling. Finally, the most promising lines of research in the modeling of isocyanates are discussed in light of the possibilities opened by novel approaches, such as machine learning.

Reaction kinetics and properties of MDI base poly (urethane-isocyanurate) network polymers

Since the trimerization of isocyanate occurs easily and controllably to form a clear trifunctional isocyanate ring, this reaction is an ideal candidate for the synthesis of a clear poly(urethane-isocyanurate) network polymer. Poly(urethane-isocyanurate) network polymer (PUI) was prepared from diphenylmethane diisocyanate (MDI) and propylene glycol (PPG) by cyclotrimerization of isocyanate group (NCO). It was proved that the expected product was successfully prepared by NCO determination, fourier transform infrared (FTIR) and gel permeation chromatography (GPC) characterization. The mechanical and thermal properties were characterized. Through the effects of catalyst dosage, polyurethane prepolymer molecular weight, reaction time, reaction temperature and MDI addition on the reaction process, it is determined that under certain other conditions, the step heating method is better for cyclotrimerization reaction. Generally, the better heating conditions are 60 °C/1 h + 80 °C/4 h + 100 °C/2 h + 120 °C/2 h + 140 °C/2 h + 160 °C/2 h. The results of thermogravimetric analysis (TGA) and mechanical properties showed that with the increase of cross-linking points in the polymer structure, the thermal stability, tensile strength, tensile modulus and hardness of PUI increased, while the elongation at break decreased significantly. The glass transition temperature (Tg) of PUI is around 45 °C, and it can be seen that the elastic modulus of the material can range from 58 to 1980 MPa. X-ray diffraction results show that the rubber phase represented by the flexible segment and the plastic phase represented by the rigid structure are amorphous.

Role of Acetate Anions in the Catalytic Formation of Isocyanurates from Aromatic Isocyanates

The formation of isocyanurates via cyclotrimerization of aromatic isocyanates is widely used to enhance the physical properties of a variety of polyurethanes. The most commonly used catalysts in industries are carboxylates for which the exact catalytically active species have remained controversial. We investigated how acetate and other carboxylates react with aromatic isocyanates in a stepwise manner and identified that the carboxylates are only precatalysts in the reaction. The reaction of carboxylates with an excess of aromatic isocyanates leads to irreversible formation of corresponding deprotonated amide species that are strongly nucleophilic and basic. As a result, they are active catalysts during the nucleophilic anionic trimerization, but can also deprotonate urethane and urea species present, which in turn catalyze the isocyanurate formation. The current study also shows how quantum chemical calculations can be used to direct spectroscopic identification of reactive intermediates formed during the active catalytic cycle with predictive accuracy.