Water-Stable Thin-Film Nanostructures from Amphiphilic Cationic Bottlebrush Block Copolymers by Grafting-through Ring-Opening Metathesis Polymerization

Well-defined and densely grafted amphiphilic cationic bottlebrush block copolymers (BBCPs) containing polystyrene (PS) and quaternary ammonium polymer (PDMH) side chains, PS-b-PDMH, were successfully generated from grafting-through ring-opening metathesis polymerization. The amphiphilic BBCP thin films, analyzed by atomic force microscopy (AFM), could self-assemble into distinct nanometer-scale domains of which the morphologies were manipulated by the volume fraction of the cationic block (f_PDMH), degree of polymerization, and asymmetric block side-chain lengths. The morphological stability of the BBCP thin films upon water exposure was investigated. The AFM images of casted BBCP films demonstrated surface roughening and morphology changes upon submersion as compared to precursor dry films, which was attributed to the swelling of the cationic domains and the rearrangement of the alkyl chain pendant groups under water. Thermally annealed films of PS-b-PDMH with an f_PDMH of 0.5 exhibited water-stable surfaces after water submersion, indicating that the BBCP structure can prevent some surface rearrangement. Such coatings could be used as potential antimicrobial and antifouling surfaces in future studies.