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.

The effect of promoting hydrogen bond aggregation based on PEMTC on the mechanical properties and shape memory function of polyurethane elastomers

In this work, small molecule diols named PEMTC were synthesized from isophorone diisocyanate, N-(2-hydroxyethyl)acrylamide and trimethylolpropane by a semi-directional method. PEMTC (2-(prop-2-enamido)ethyl N-{3-[({[2-ethyl-3-hydroxy-2(hydroxymethyl)propoxy]carbonyl}amino)methyl]-3,5,5-trimethylcyclohexyl}carbamate) contains hydrogen bond active site and light-initiated C=C. We introduced it as a branch chain block into poly(ε-caprolactone) (PCL). By feeding and monitoring the reaction process, we synthesized a large number of polyurethane elastomers, hydrogen bonds PCL-based elastomer (HPE), which contain a large number of dynamic hydrogen bonds. Under UV irradiation, PEMTC can make HPE molecules aggregate and cross-link, improve the degree of internal hydrogen bonding interaction of HPE materials and endow HPE materials with good elasticity, toughness, heat resistance and shape memory ability. After 270 nm UV irradiation, the elongation at break of HPE materials decreased from 607.14-1463.95% to 426.60-610.36%, but the strength at break of HPE materials increased from 3.36-13.52 to 10.28-41.52 MPa, and the toughness increased from 16.36-129.71 to 40.48-172.22 MJ m-3. In addition, the highest shape fixation rate of HPE after UV irradiation was 98.0%, and the recovery rate was 93.7%.

Strongly Polarized Iridiumδ--Aluminumδ+ Pairs: Unconventional Reactivity Patterns Including CO2 Cooperative Reductive Cleavage

The iridium tetrahydride complex Cp*IrH₄ reacts with a range of isobutylaluminum derivatives of general formula Al(iBu)_x(OAr)_3-x (x = 1, 2) to give the unusual iridium aluminum species [Cp*IrH₃Al(ⁱBu)(OAr)] (1) via a reductive elimination route. The Lewis acidity of the Al atom in complex 1 is confirmed by the coordination of pyridine, leading to the adduct [Cp*IrH₃Al(ⁱBu)(OAr)(Py)] (2). Spectroscopic, crystallographic, and computational data support the description of these heterobimetallic complexes 1 and 2 as featuring strongly polarized Al(III)^δ+-Ir(III)^δ- interactions. Reactivity studies demonstrate that the binding of a Lewis base to Al does not quench the reactivity of the Ir-Al motif and that both species 1 and 2 promote the cooperative reductive cleavage of a range of heteroallenes. Specifically, complex 2 promotes the decarbonylation of CO₂ and AdNCO, leading to CO (trapped as Cp*IrH₂(CO)) and the alkylaluminum oxo ([(iBu)(OAr)Al(Py)]₂(μ-O) (3)) and ureate ({Al(OAr)(ⁱBu)[κ²-(N,O)AdNC(O)NHAd]} (4)) species, respectively. The bridged amidinate species Cp*IrH₂(μ-CyNC(H)NCy)Al(ⁱBu)(OAr) (5) is formed in the reaction of 2 with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond activation processes.