Synthesis and Self-assembly of a Triarm Star-shaped Rod-Rod Block Copolymer

We designed and synthesized a triarm star-shaped rod-rod block copolymer (BCP), (poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl] styrene}-block-poly(gamma-benzyl-(L)-glutamate))(3), (PMPCS-b-PBLG)(3). The triarm core with three PMPCS-N-3 segments was prepared by copper-mediated atom transfer radical polymerization of 2,5-bis[(4-methoxyphenyl)-oxycarbonyl] styrene initiated by a trifunctional initiator and a subsequent azide reaction. And the PBLG block with alkyne functionality was synthesized through ring-opening polymerization of gamma-benzyl-(L)-glutamate N-carboxyanhydride initiated by propargylamine. Finally, Huisgen's 1,3-dipolar cycloaddition was employed to combine the triarm (PMPCS-N-3)(3) and PBLG segments. The chemical structure of the BCP was confirmed by H-1-NMR spectroscopy, Fourier-transform infrared spectroscopy, and gel permeation chromatographic analysis. Results from differential scanning calorimetry, polarized light microscopy, one-dimensional and two-dimensional wide-angle X-ray diffraction, and transmission electron microscopy techniques demonstrate that the triarm star-shaped rod-rod BCP self-assembles into a hexagon-in-lamella morphology, with the PMPCS block in the columnar nematic phase and the PBLG block in the hexagonal columnar arrangement packed in bilayers due to the rigid nature of the two blocks and the covalent connections in the star-shaped BCP.