Synthesis and self-assembly of a linear coil-coil-rod ABC triblock copolymer

An interesting order-order transition between two different complex nanostructures was observed in a new liquid crystalline linear coil-coil-rod ABC triblock copolymer (triBCP). First, the ABC triBCP, poly(dimethylsiloxane)-bpolystyrene-b-poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PDMS-b-PS-b-PMPCS), was synthesized through sequential atom transfer radical polymerization. The degrees of polymerization of PDMS, PS, and PMPCS blocks are 58, 159, and 106, and the corresponding volume fractions of PDMS, PS, and PMPCS are 0.09, 0.29, and 0.62, respectively. The phase behaviors of the PDMS-b-PS diblock copolymer precursor and the final triblock copolymer were studied by smallangle X-ray scattering, one-dimensional wide-angle X-ray scattering, and transmission electron microscopy experiments. The PDMS-b-PS precursor self-assembles into hexagonally packed cylinders with a relatively small periodic size after thermal annealing. When the triblock copolymer is annealed at a relatively low temperature (120 °C) at which the PMPCS block is in the amorphous state, the triBCP forms core-shell hexagonally packed cylinders (CSH) with a relativly large periodic size. After the triBCP is annealed above 140 °C at which the PMPCS block transforms to the liquid crystalline (LC) phase, the nanophase-separated structure transforms to a three-phase four-layer lamellar structure (LAM-3P4L). Thus, accompanied with the transition of the PMPCS blocks from the amorphous state to the LC phase, the order-order transition from CSH to LAM-3P4L occurs in the PDMS-b-PS-b-PMPCS ABC triBCP.