Preparing DNA-mimicking multi-line nanocaterpillars via in situ nanoparticlisation of fully conjugated polymers

A unique hierarchical evolution from single-line nanocaterpillars to multi-line nanocaterpillars and then to multi-line nanocaterpillars bearing a few long-chain branches was demonstrated by in situ nanoparticlisation of fully conjugated poly(2,5-dihexyloxy-1,4-phenylene)-block-poly(3-methylthiophene) (PPP-b-P3MT). PPP-b-P3MTs of various block ratios were successfully synthesised by the Grignard metathesis polymerization method; moreover, these block copolymers underwent spontaneous self-assembly during the polymerization owing to the solvophobicity or strong π–π interactions of the core block, i.e. P3MT. These in situ generated PPP-b-P3MT NPs were quite different from the previously reported NPs generated from poly(2,5-dihexyloxy-1,4-phenylene)-block-polythiophene (PPP-b-PT). AFM and TEM images revealed that PPP-b-P3MTs formed single- to multi-line nanocaterpillars, whereas PPP-b-PTs only formed shorter single-line nanocaterpillars. On the basis of PXRD and UV–vis data, we speculated that this interesting morphology of multi-line nanocaterpillars, resembling duplex DNA, arose from different packing modes and crystallinity as well as improved solubility of the P3MT core compared with the NPs containing the PT core.