In this work, the amine-epoxy “click” reaction is shown to be a valuable general tool in the synthesis of reactive hydrogels. The practicality of this reaction arises due to its catalyst-free nature, its operation in water, and commercial availability of a large variety of amine and epoxide molecules that can serve as hydrophilic network precursors. Therefore, hydrogels can be prepared in a modular fashion through a simple mixing of the precursors in water and used as produced (without requiring any post-synthesis purification step). The gelation behavior and final hydrogel properties depend upon the molecular weight of the precursors and can be changed as per the requirement. A post-synthesis modification through alkylation at the nitrogen atom of the newly formed β-hydroxyl amine linkages allows for functionalizing the hydrogels. For example, ring-opening reaction of cyclic sulfonic ester gives rise to surfaces with a zwitterionic character. Finally, the established gelation chemistry can be combined with soft lithography techniques such as micromolding in capillaries (MIMIC) to obtain hydrogel microstructures.

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A novel blocked isocyanate crosslinker was synthesized, and its applicability was investigated for the low-temperature curing of automotive clearcoats. Various pyrazole derivatives were prepared as blocking agents in isocyanate crosslinkers, which strongly affect the deblocking and curing properties of the urethane-bonded coating systems. The thermal curing properties of clearcoat samples containing a pyrazole-based blocked isocyanate crosslinker and polyol resin were characterized under two different temperature conditions (120 and 150 °C). The decrease in the amount of hydroxyl groups in the polyol before and after curing was expressed by the change in OH stretching frequency in the Fourier transform infrared (FT-IR) spectra. The real-time rheological storage moduli of the bulk clearcoat mixtures were measured via a rotational rheometer to determine the effect of pyrazole-based blocking agents on the curing dynamics. In addition, a rigid-body pendulum tester (RPT) was employed to investigate the curing behavior in the thin film form. The nano-indentation and the nano-scratch tests were conducted to examine the surface hardness and scratch resistance characteristics of the cured clearcoat films. The results show that a low-temperature curing system of clearcoats can be realized by tuning the curing temperature and reactivity of isocyanate crosslinkers blocked with pyrazole-based substituents.

The real-time curing behaviors and surface mechanical properties of two curable systems, polydimethylsiloxane (PDMS) and poly(ethylene glycol) (PEG) films containing different portions of glycidyl methacrylate (GMA), were investigated via various measurements for potential application as anti-fouling coatings. In these mixtures, methacryloxypropyl-terminated PDMS and poly(ethylene glycol)dimethacrylate were used as the difunctional crosslinkers, and GMA was employed as the epoxy component. During the coating process, UV irradiation generated network structures for both mixtures (PDMS-GMA and PEG-GMA), while they exhibited the different evolution of the elastic modulus with respect to the GMA content. It was found that a small portion of the crosslinkers formed at early stage has a dominant contribution to the overall film properties, leading to a small swelling ratio and large gel fraction. The indentation and scratch mechanical properties of the cured films were qualitatively well linked with the real-time rheological data for the curable mixtures acquired during the curing process.

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