Direct synthesis of poly(N-alkyl acrylamide) (co)polymers with pendant reactive amino groups by organocatalyzed amidation of polymethylacrylate

Post-polymerization modification of poorly reactive polyacrylates using efficient catalytic transesterification and amidation reactions has recently emerged as a valuable tool to access diversely functionalized poly(meth)acrylates and poly(meth)acrylamides. The method is particularly useful to introduce functional groups incompatible with the polymerization mechanism, such as non-protected reactive amino groups. In this work, we explored the TBD-catalyzed amidation of polymethylacrylate (PMA) with various difunctional amines to obtain polyacrylamide homo- and copolymers with a pendant reactive amine group. As anticipated, functional polymers could not be attained from amidation with ethylenediamine, because of competing cross-linking side reactions, but could be prepared from the mono-Boc-protected ethylenediamine instead, requiring, however, additional unwanted protection and deprotection steps. More interestingly, we found that the direct amidation of PMA with unprotected N-ethylethylenediamine is an efficient method for preparing secondary amine functionalized polymers, without the occurrence of crosslinking side-reaction even at lower catalyst loading. The crucial role of the ethyl group to prevent side reactions was clearly demonstrated as the use of N-methyl ethylenediamine led to crosslinking. The utility of the developed platform for the rapid preparation of a series of hydrophilic copolymers and hydrogel materials is also demonstrated. The hydrogels were prepared by reacting the secondary amine side chains with methacrylic anhydride, followed by photocuring in the presence and absence of dithiols.