Surface hydrophobic modification of materials by carbene chemistry

Most synthetic plastic, such as polyurethane: a thermoplastic polymer that contains a NHCOO chemical group, have been successfully employed in preparation of resins, foams, coatings, adhesives, fibers and insulations, mainly via the reaction of isocyanates with hydroxyl compounds. With the global focus shifted towards the development of environmental regenerating substances, waterborne polyurethanes have gained significant scholarly and commercial interest owing to their potential to reduce environmental pollution. Unfortunately, such waterborne polyurethanes contain either hydrophilic soft segments such as polyethylene glycols, or pendant acid or tertiary amine group. These functional groups contribute to the hydrophilicity of the waterborne polyurethanes, making them more culpable to destruction due to moisture and water ingress. Accordingly, there is need to surface-tailor polyurethanes and make them more hydrophobic in order to allow for application in advanced technology systems.

To this note, a team of researchers led by associate professor Pengfei Yang at Qilu University of Technology, Jinan, China, proposed a study whose main objective was to utilize diaryl diazomethane with dodecyl groups to generate highly reactive diaryl carbene intermediates under solar-light conditions and use it to induce hydrophobicity to the surface of polyurethanes. Their work mainly focused on synthesis and characterization of the surface-modified hydrophobic polyurethanes. Their work is currently published in the research journal, Applied Surface Science.

The research method commenced with the synthesis of dodecyl diaryl diazomethane from 4,4-dihydroxybenzophenone and 1- bromododecane by a series of reaction steps. Next, the researchers prepared the water-borne polyurethane films with different amount of 2,2-dimethylol propionic acid (DMPA), as well as a type of solvent-borne polyurethane film for comparison. The prepared polyurethane films were modified by dodecyl diaryl diazomethane. The researchers then employed the contact angle test to characterize the films and depict their surface property. Lastly, the DSC analysis and tensile test were used to investigate the physical properties of polyurethane films before and after modification.

The authors observed that the contact angle of waterborne polyurethane films was enhanced greatly after modification, and the surface property changed distinctly from hydrophilicity to hydrophobicity. Moreover, the modified polyurethane films showed higher glass transition temperature, namely, higher thermal stability. the researchers noted that the modified waterborne polyurethane films could be compared with the solvent-borne polyurethane films on physical property.

The study by Pengfei Yang and colleagues successfully presented the fabrication of water-borne polyurethane films and its subsequent post-modification by carbene chemistry. The surface modified polyurethane coatings exhibited excellent hydrophobic properties that were ideal for utilization in marine environments (Applied Surface Science, 2018, 435, 346. and Journal of Applied Polymer Science, 2018, 135, 46421.). Moreover, the fluoro diaryl carbenes of similar use were synthesized and used for the post-modification of electrospun gelatin membrane, and this membrane was used for the selective oil/water separation (ACS Omega, 2018, 3, 3928. and Materials Letters, 2018, 210, 295.). Altogether, the hydrophobic modification protocol with carbene insertion has found new application on polymeric coatings, and the discovery has potential to open a new horizon for expediently preparing hydrophobic materials under direct solar-light exposure.