Synthesis and properties of polyetherketone-block-polybenzobisthiazole-block-polyetherketone ABA triblock copolymers

Abstract

As an approach to rigid-rod molecular composites, a series of PEK-b-PBZT-b-PEK ABA triblock copolymers were synthesized. Three different types of polyetherketones (PEKs) as coil A-block units and the carboxylic acid-terminated polybenzobisthiazoles (PBZTs) with two different molecular weights as rigid-rod B-block units were utilized to afford the targeted ABA triblock copolymers. The resulting triblock copolymers were insoluble in common polar aprotic solvents such as N-methylpyrrolidinone, dimethylformamide, dimethyl-acetamide, and dimethyl sulfoxide but showed greatly improved solubility in strong acids such as trifluoroacetic acid, methanesulfonic acid (MSA), trifluoromethanesulfonic acid, and sulfuric acid. Good quality films could be cast from solutions. Alternatively, we could also process these copolymers by the compression molding technique. The block copolymer samples were simply heated above the transition temperatures of the coil components and pressed into articles with desired shapes. The wide-angle X-ray diffraction study of the selected solution-cast film exhibited a long-range ordering, which is indicative of microphase separation. This was further confirmed by the results from small-angle X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In addition, the UV-vis absorption behavior of the copolymer solutions implied that the ground state conformations of PBZT in MSA were greatly dependent on the amorphous or the semicrystalline nature of the PEK unit, which has little or no effect on the emission properties.