Le Thu Thi Nguyen

Kinetic comparison of 13 homogeneous thiol–X reactions

An extensive kinetic comparison of 13 thiol–X reactions is presented using online FT-IR. Besides the effect of catalysts (tertiary phosphine or tertiary amine), a significant catalytic effect of dipolar solvents on many thiol–X reactions is observed. Thus, different overall reactivity orders of the studied substrates toward the thiol group are shown in polar aprotic and nonpolar solvents and compared with previous results in analogous heterogeneous reactions. The reactivities of some substrates toward n-octylamine are also investigated and their reactions with the amine and the thiol are compared. This study can serve as a useful guide for the choice and application of many thio-click reactions as efficient chemical conjugation tools.

Providing polyurethane foams with functionality: a kinetic comparison of different “click” and coupling reaction pathways

For high-tech applications, polyurethane (PU) materials require additional surface properties and functionality, which can be achieved by incorporation of “clickable” groups in the PU structure, allowing for polymer post-modification via chemical coupling with desired molecules. Therefore, in this study, various “click” and coupling reactions, consisting of the copper(I) catalyzed Huisgen 1,3-dipolar alkyne–azide, thermally and photo-initiated thiol–ene/thiol–yne and Diels–Alder reactions, have been used for surface functionalization of PU foams. As a result of diffusional effects, the reaction rate was considerably depressed and thus, the reaction parameters, including the temperature and the concentration of reagents and the “click” compound, were optimized for each click/coupling approach to obtain high functionalization yields. As such, a kinetic comparison study of the different chemistries used was performed, using in situ FT-IR and offline 1H NMR methods. This work not only reveals kinetic trends but also compares promising and limiting aspects of the different click/coupling pathways employed, which is envisaged to be also useful for functionalizing other cross-linked polymeric materials.

Efficient microencapsulation of a liquid isocyanate with in situ shell functionalization

We report on a one-pot, facile approach for the encapsulation of the liquid hexamethylene diisocyanate isocyanurate trimer in polyurea microcapsules formed via the oil-in-water interfacial reaction of an uretonimine-modified diphenyl methane diisocyanate trimer with triaminopyrimidine, with in situ shell functionalization/modification using different types of hydrophobic agents. Remarkably, the use of hexamethylenedisilazane resulted in microcapsules of about 70 μm in diameter, with a smooth outer surface and a high isocyanate core content up to 85 wt% as determined by quantitative online FT-IR analysis of the extracted core. On the other hand, the use of an alkylamine, fluorinated aromatic amine and/or perfluoride amine provided microcapsules of approximately 100 to 150 μm in diameter containing around 65–75 wt% of the isocyanate core content, with the outer shell surface bearing pendant hydrophobic groups as confirmed by SEM-EDX. The effects of the functionalizing compound on the microcapsule properties such as shell morphology, size distribution and stability were assessed. After one day immersion in water, the initial isocyanate content of the microcapsules with a non-functionalized shell dropped rapidly from 49 to 15 wt%, whereas the ones with the modified shell structure maintained their core content, suggesting a significantly enhanced microcapsule stability.