Polymer coating by oxidative polymerization of a new dopamine analogue with two amino groups

In our quest to expand the comprehensive chemistry of polydopamine and its catechol-containing analogous adhesive polymers we developed a new monomer, specifically 4-[3-amino-2-(aminomethyl)propyl]benzene-1,2-diol ADA . This compound is an analogue of dopamine characterized by an elongated and branched alkyl side chain that incorporates two amino groups. ADA was synthesized in two steps from 3,4-dihydroxybenzaldehyde in high yields. Exposure to air in aqueous Tris solution initiated polymerization leading to a dark colored product PADA that can adhere to surfaces forming continuous layers. The product was analyzed by FTIR, NMR, UV–vis-spectroscopy, AFM, HR-ESI-MS spectrometry, XPS, DPV, DLS and contact angle measurement. Based on these analyses, a general structure of the product is proposed as along with a mechanism of its formation. Notably, the properties of PADA are distinct from those of polydopamine offering different potential application. In particular, the additional amino groups could be used for interesting linkage of other functional moieties. • New dopamine homologue with two amino group. • Straight forward polymer formation by air oxidation in buffered water. • Formation of smooth coatings of 6 nm at different surfaces. • More amino groups in comparison to polydopamine, less negative Zeta potential. • Interesting reaction mechanism also showing new reactions as compared with PDA.