Development of supramolecular liquid-crystalline polyurethane complexes exhibiting triple-shape functionality using a one-step programming process

Abstract

Supramolecular liquid crystalline polymers and shape memory polymers are attracting increasing interest as materials. In this paper, we describe the development of a supramolecular liquid crystalline shape memory polyurethane (SLCSMPU) complex that exhibits both liquid crystalline properties and shape memory properties. The complex is formed by incorporating 4-hexadecyloxybenzoic acid (HOBA) into a pyridine-containing shape memory polyurethane (PySMPU). The HOBA is tethered to the PySMPU by strong hydrogen bonding between the pyridine rings and the COOH of the HOBA, forming a SLCSMPU complex. Heat treatment plays an important role in the formation of hydrogen-bonded supramolecular liquid crystalline structures in these SLCSMPU complexes. Thus, the SLCSMPU complex not only maintains the intrinsic liquid-crystalline properties of HOBA, but can also form a stable polymeric film for various shape memory applications. Additionally, the SLCSMPU complex forms a two-phase separated structure composed of an amorphous polyurethane matrix and a HOBA crystalline phase, which includes the hydrogen-bonded crystalline HOBA phase and the free HOBA crystalline phase. Therefore, a simple one-step programming process is developed that produces SLCSMPU complexes with excited triple-shape functionalities due to their multiple phase transitions, especially when the molar ratio of HOBA/BINA is less than 0.8.