Preparation of High Performance Dielectric Elastomers by Tailoring the Aggregation Structure of Polyurethane

The phase structure, crystallization and hydrogen bonding of thermal polyurethane (TPU) were controlled by annealing process. And the modulus and dielectric constant (epsilon') of TPU were tailored to improve the electromechanical properties of TPU. Scanning electron microscopy (SEM) and small angle X-ray (SAXS) were used to study the crystalline structure of TPU. The changes of hydrogen bonding of TPU were semi-quantitatively analyzed by infrared spectroscopy. The microphase separation structure of TPU was studied by atomic force microscope (AFM). The results show that changing annealing temperature and time results in complex aggregation structures, thus leading to very different electromechanical properties. After annealing at 80 degrees C, large numbers of soft segment crystals were formed with the hard phase distributing in the continuous soft phase. Both phase separation and the destruction of hydrogen bonding were improved compared with those of 150 degrees C annealing treatment. Therefore, higher epsilon' and lower modulus were obtained, resulting in larger actuated strain. Besides, under the condition of low temperature annealing, a wide range of soft segment crystals were produced, which makes the molecular chains of soft segments closely arranged, resulting in a significant increase in the breakdown strength of TPU. The results show that after annealing at 80 degrees C for 6 h, the electrical breakdown strength of TPU increases from 25 kV/mm to 32 kV/mm, and the maximum actuated strain increases from 0.77% to 3.3%, increased by 4.3 times. [GRAPHICS] .