Tuning the Chirality of Block Copolymers: From Twisted Morphologies to Nanospheres by Self-Assembly

New advances into the chirality effect in the self-assembly of block copolymers (BCPs) have been achieved by tuning the helicity of the chiral-core-forming blocks. The chiral BCPs {[N=P(R)-O2C20H12](200-x)[N=P(OC5H4N)(2)](x)}-b-[N=PMePh](50) ((R)-O2C20H12=(R)-1,1'-binaphthyl-2,2'-dioxy, OC5H4N=4-pyridinoxy (OPy); x=10, 30, 60, 100 for 3a-d, respectively), in which the [N=P(OPy)(2)] units are randomly distributed within the chiral block, have been synthesised. The chiroptical properties of the BCPs ([alpha](D) vs. T and CD) demonstrated that the helicity of the BCP chains may be simply controlled by the relative proportion of the chiral and achiral (i.e., [N=P(R)-O2C20H12] and [N=P(OPy)(2)], respectively) units. Thus, although 3a only contained only 5% [N=P(OPy)(2)] units and exhibited a preferential helical sense, 3d with 50% of this unit adopted non-preferred helical conformations. This gradual variation of the helicity allowed us to examine the chirality effect on the self-assembly of chiral and helical BCPs (i.e., 3a-c) and chiral but non-helical BCPs (i.e., 3d). The very significant influence of the helicity on the self-assembly of these materials resulted in a variety of morphologies that extend from helical nanostructures to pearl-necklace aggregates and nanospheres (i.e., 3b and 3d, respectively). We also demonstrate that the presence of pyridine moieties in BCPs 3a-d allows specific decoration with gold nanoparticles.