Preparation of defect-free nanocaterpillars via in situ nanoparticlisation of a well-defined polyacetylene block copolymer†
Previously we reported a one-pot preparation of nano-objects resembling a caterpillar (nanocaterpillar) from polyacetylene (PA) diblock copolymers, via the in situ nanoparticlisation of conjugated polymers (INCP) approach. However, they showed the following limitations: micro-structure of PA block was stereo-random containing mixtures of E and Z polyenes, and their nanostructures were contaminated by nanosphere defects. Herein, we report strategies to prepare not only defect-free nanocaterpillars, but also the stereo-regular PA diblock copolymers. By altering the ROMP temperature, we can control the stereochemistry (E/Z) of the PA block, the degree of chain-transfer reaction and molar mass dispersity. As a result of a suppressed chain-transfer reaction at low temperature, ROMP of cyclooctatetraene (COT) at 0 °C produced defect-free nanocaterpillars containing cis-major PAs and they can be transformed into those containing trans-major PAs by thermal isomerisation. Compared to previously reported ill-defined block copolymers, these well-defined block copolymers lead to an increase in the length of nanocaterpillars and narrower length distribution.