Yong De Han

Bio: Yong De Han is an academic researcher. The author has contributed to research in topics: Reaction rate & Reaction rate constant. The author has an hindex of 4, co-authored 5 publications receiving 52 citations.

The reaction of o-hydroxybenzyl alcohol with phenyl isocyanate in polar solvents

Abstract: The reaction of o-hydroxybenzyl alcohol with phenyl isocyanate has been investigated in different polar solvents with in situ FT-IR. The rate constants for the reactions of the phenolic hydroxyl group and the aliphatic hydroxyl group were calculated as k 1 and k 2, respectively. It is found that the phenolic hydroxyl group reacts more easily than the aliphatic hydroxyl group. It is also found that k 1 increases with increasing solvent polarity, while the trend of k 2 is the opposite. Moreover, the reaction kinetics is second-order with respect to toluene, butyl acetate, cyclohexanone and pyridine, but is first-order with respect to NMP and DMF without distinction for the two kinds of hydroxyl groups.

Effects of solvent polarity on the reaction of phenol with tolylene‐2,4‐diisocyanate

Abstract: Using tolylene-2,4-diisocyanate as standard compound, the relationship between NCO absorbance and concentration was studied with in situ FTIR. The linear relationship appeared correct only for concentrations lower than 0.4 mol L−1. Then, the urethane reaction kinetics of phenol with tolylene-2,4-diisocyanate were investigated in different solvents, such as dimethyl sulfoxide, cyclohexanone, n-butyl acetate, 1,4-dioxane, and xylene. It showed that solvents largely affected reaction rates. The reaction was largely accelerated in polar solvents, following the order of dimethyl sulfoxide > cyclohexanone > n-butyl acetate > 1,4-dioxane > xylene. It was in contrast to the alcohol–diisocyanate reaction. Finally, an appropriate reaction mechanism was proposed. The HO bond in phenol was polarized under the influence of solvents, which made the combination of hydrogen to nitrogen and alkoxyl group to carbenium easier. After that the solvent was dissociated and the carbamate generated. The kinetic equation could be derived as v = k′K·[S:] [ROH]·[R′NCO]. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of Substituents and Solvents on Phenol-Isocyanate Urethane Reaction

Abstract: In this study, the urethane reaction of several phenols with isocyanate was monitored with in-situ FT-IR Reaction rate constants were calculated out to investigate the effect of substituents in phenols, as well as the polarity of different solvents It showed that the polarity of solvents largely affected the reaction rate even without catalyst The reactivity increased in the following order: Xylene

Synthesis of Polyurethanes Using Organocatalysis: A Perspective

Abstract: Organocatalysis has become an invaluable tool for polymer synthesis, and its utility has been demonstrated in ring-opening, anionic, zwitterionic, and group-transfer polymerizations. Despite this, the use of organocatalysis in other polymerization reactions such as step-growth polymerizations remains underexplored, relative to more traditional metal-based polymerizations. Recently, the use of organic bases such as guanidines, amidines, N-heterocyclic carbenes, and organic “strong or super-strong” Bronsted acids to catalyze the synthesis of metal-free polyurethanes has shown to be competitive to commercially widely used dibutyltin dilaurate and dibutyltin diacetate catalysts. This Perspective article highlights recent advances in organocatalyst design for isocyanate-based polyurethane synthesis with the aim of comparing the activity and selectivity of each of the new catalytic reactions to each other and the traditional metal-based catalysts. The article also draws attention to new trends in isocyanate-fre...

A facile dynamic crosslinked healable poly(oxime-urethane) elastomer with high elastic recovery and recyclability

Abstract: Endowing thermoset polymer materials with self-healing and recyclable properties by incorporating dynamic bonds into the polymer networks is of vital realistic significance. However, such materials are still limited because of the difficult synthetic process and expensive dynamic monomers or environment-unfriendly catalysts. Herein, catalyst-free and colorless transparent healable and recyclable poly(oxime-urethane) elastomers based on dynamic oxime–carbamate bonds were developed with scaling-up capability using low-cost and commercially available compounds. These materials display remarkable comprehensive properties and relatively low relaxation activation energy (∼29.7 kcal mol−1) which results in excellent healable and recyclable performance. The poly(oxime-urethane) with a crosslink density ν of ∼0.2 mmol cm−3 possesses a tensile strength of ∼13.5 MPa, a breaking strain of ∼812%, toughness up to ∼40 MJ m−3, an excellent elastic recovery of ∼90% and an average optical transmittance of ∼86% in the visible range. This material can be completely healed at 110 °C in 0.5 h. In situ structural characterizations revealed that the dynamic properties originate from the reversibility of oxime–carbamate bonds and hydrogen bonds.

Study of inkjet printing as additive manufacturing process for gradient polyurethane material

Abstract: Reactive inkjet printing as additive manufacturing technique is evaluated for generation of gradient material made from polyurethane. Therefore dots are fabricated in situ by drop-into-drop inkjet printing of three separate components (2 polyols, 1 isocyanate) successively from three separate print heads. Changing the mixing ratio of the three components enables tailoring of the mechanical properties for each voxel, which raises the potential for printing of gradient materials. This study does not examine the complete additive manufacturing process to build whole 3D objects but its focus is set on the behavior of the printing heads and the printability of the components as well as on properties of the produced material. Regarding the gradient properties it is necessary to ensure that the stoichiometric ratio is given for all mixtures and that the printable masses of each component comply with the desired resolution, i.e. the smallest size of one voxel. This requires determination of the printing parameters and a definition of the achievable range of mechanical properties (e.g. hardness, elastic modulus) which is done in this study by evaluation of casted specimen from polyurethane. Additionally in this study inkjet printability of the polyols and the polyisocyanate in dependence of different fractions of toluene as a solvent is evaluated by determination of the Ohnesorge number Oh. Easily measurable physical properties as density, surface tension and viscosity are determined for several fractions of toluene to calculate 1/Oh. Finally reactive inkjet printing technology with the optimized liquids is used to create dots to form polyurethane.