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

Abstract

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 3 a-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 ([α]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 3 a only contained only 5% [N=P(OPy)2] units and exhibited a preferential helical sense, 3 d 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., 3 a-c) and chiral but non-helical BCPs (i.e., 3 d). 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., 3 b and 3 d, respectively). We also demonstrate that the presence of pyridine moieties in BCPs 3 a-d allows specific decoration with gold nanoparticles.