RAFT synthesis, properties and morphologies via thermal annealing of new azo-based ABA triblock copolymers bearing rigid and soft segments

Abstract

In this study, a series of novel ABA-type triblock azo-copolymers (TBCs) consisting of PEG and PCAEMA segments were synthesized by RAFT polymerization. The TBCs were characterized by ¹H-NMR, GPC, DSC, OPM, AFM, GISAXS, and UV-vis. Number-average molecular weight (≤34,200 g/mol) and molecular weight distribution (≤1.44) were slightly increased with increasing the feed molar ratio of monomer to macroinitiator. This indicates a controlled/living polymerization with good distribution. All TBCs displayed transitions attributed to smectic-to-nematic and nematic-to-smectic phases at 108 °C and 104 °C, respectively. TBC with 34 wt% azobenzene displayed fan-shaped focal conic texture, while TBCs containing 46, 53, 58, 63, and 71 wt% azobenzene revealed batonnet textures. TBC-3 and TBC-4 having 53 and 58 wt% azo contents produced lamellar and a mixture of cylinder and lamellar nanostructures compared to other TBCs, which formed hexagonal cylindrical nanostructures. Every TBCs exhibited photoresponsive behavior under UV irradiation and thermal relaxation.

Keywords:

• Self-assembly
• thermal transitions
• mesophase
• photoresponsive behavior
• morphology

Acknowledgments

A. Z. acknowledges the support of Hanyang University (HU) to this study. A. Z. expresses his respectful gratitude to all collaborators who have made contributions to this work. A. Z. is grateful to HU for using its facilities and providing an excellent atmosphere to carry out this research. A. Z. is thankful to Prof. Yang-Kyoo and Dr. Je-Gwon for their advice and help during the experiments.

Disclosure of potential conflicts of interest

There are no conflicts to declare.