Block copolymers of N-hexadecyl-4-vinylpyridinium bromide (4VPC(16)Br) and N,N-dimethylacrylamide (DMAA) were synthesised by nitroxide-mediated radical polymerisation using 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) as a control agent. The behaviour of such block copolymers in aqueous medium was then investigated in relation to the respective size of both the amphiphilic and the hydrophobic block. Viscosimetry, surface tension measurements, and fluorescence spectroscopy revealed that intramolecular hydrophobic microdomains were spontaneously formed by the pendent long alkyl chains. The properties of the corresponding microdomains were determined in terms of polarity and local cohesion, and were revealed to depend on the relative length of the blocks in the copolymer.