An ABA triblock containing a central soft block of poly[2,5-di(n-hexogycarbonyl) styrene] and outer hard block of poly(4-vinylpyridine): synthesis, phase behavior and mechanical enhancement

We designed and synthesized a series of ABA triblock copolymers containing an inner soft poly[2,5-di(n-hexogycarbonyl) styrene] (PHCS) block and an outer hard poly(4-vinylpyridine) (P4VP) block, wherein the PHCS block has the potential to form a columnar liquid crystalline phase at high temperatures and the P4VP block can complex with metal salt or organic molecules via non-covalent interactions. Using an atom transfer radical polymerization method, we prepared successfully the triblock samples with controlled molecular weights (MWs) and compositions. The triblocks were characterized with various experimental techniques including differential scanning calorimetry, dynamic mechanical analysis, small-angle X-ray scattering, and transmission electron microscopy. The experimental results indicate the occurrence of microphase separation. With the P4VP volume fraction lower than 20%, the triblocks exhibit the phase morphologies of cylindrical or spherical hard P4VP domains arranged in the soft PHCS matrix. Mechanical property testing reveals that the tensile strength and maximum elongation at break can be tuned by varying the total MW and composition of the samples, indicating that the triblock copolymer can be used as thermoplastic elastomer while carrying functional blocks. Applying the metal-ligand coordination interaction between P4VP and Zn2+, we prepared the hybrid of triblock and zinc perchlorate. Domain spacing expansion and phase morphology change induced by adding the metal salt are detected. Furthermore, because of the hybrid formation and the glass transition temperature of hard phase increased dramatically by adding only a small amount of the salt, the rubbery plateau of the hybrid is extended, indicating a better thermal stability than that of the pure triblock.