Synthesis and Shape Memory Property of a MDI Based Liquid Crystalline Polyurethane

Liquid crystalline polyurethanes (LCPU) were prepared from 4,4’-methylenediphenyl diisocyanate (MDI), 1,6-hexanediol (HDO), 2,2-dimethylol propionic acid (DMPA) and polytetramethylene ether glycol (PTMG). The experiments synthesized three liquid crystalline polyurethane films with different soft/hard segment ratio. Chemical and structural characterization of the polyurethanes were investigated by Fourier transform infrared, X-ray diffraction, thermogravimetric analysis, differential scanning calorimeter and polarized microscopy respectively. Swelling rate and shape memory property were tested. The results indicated that the polyurethane with 62% soft segment and large group of carboxyl displayed excellent swelling and shape memory properties, and the shape recovery rate reached 100%. It was found that the crystallinity, thermal stability decreased and the temperature flexibility, water absorption and shape recovery rate increased with the increase of polytetramethylene ether glycol.