Biomimetic polymers adhesives have confirmed their great potential to overcome the issues related with low adhesion in humid conditions. Indeed, following the example of how mussels can strongly and easily adhere to reef, catechol moieties have been incorporated into several polymer chains such as styrene, acrylic acid or lactic acid to boost adhesion strength in wet environment. In particular poly(catechol-co-styrene) outperformed every other commercial adhesives when tested underwater, leading to adhesion values up to 3 MPa.

In order to ease the synthesis of this poly(catechol-co-styrene) and increase its potential commercial availability, a novel synthetical protocol was designed that encompassed monomer synthesis, polymerization in suspension and final catechol deprotection. Hence, 3,4-dimethoxystyrene was obtained in a convenient two steps reaction from 3’,4’-dimethoxyacetophenone, a highly available and affordable small molecule. Then, the suspension polymerization conditions were tuned, e.g. stabilizers concentration, stirring speed and vessel and blade diameters, to afford the most suitable polymer molecular weight and dispersity for adhesion. Finally, diverse methoxy ether cleavage agents were tested to deprotect the methoxy groups. The best results in term of deprotection efficiency and polymer purification were obtained while using iodocyclohexane. Following this procedures, poly(catechol-co-styrene) batches of up to 60 g with a Mw of 190 kg.mol^-1 and dispersity of 3.5 were prepared.

Finally, the adhesion strength of the poly(catechol-co-styrene) prepared following the hereby presented protocol was compared with the one obtained following the previous anionic polymerization (table 1). Whereas the adhesion values appeared to be slightly lower in dry conditions with the suspension polymerization protocol, the adhesion values were equal when the adhesive was applied and cured under seawater conditions.

Table 1: Adhesion strength of poly(catechol-<i>co</i>-styrene) when prepared following the suspension or the anionic polymerizations.

Table 1: Adhesion strength of poly(catechol-co-styrene) when prepared following the suspension or the anionic polymerizations.

Cindy Atencio-Martinez

Appearances