Preparation And Properties Of CuPc/PU Composites With High Dielectric Constant

Electroactive polymers (EAPs), which can realize electromechanical conversion under an external electric field, are attractive for a broad range of applications such as sensors, actuators and microelectromechanical systems. However, the low dielectric constant of a polymeric material is one of the key factors which limit the EAPs applications. Copper phthalocyanine oligomer (CuPc) has a very high dielectric constant and lower elastic modulus compared with ceramics. Therefore, when CuPc was incorporated in polymer matrix, the composite still take advantages like easy processing and good flexibility.In this thesis, CuPc was synthesized by solution method and successfully grafted with poly(p-chloromethyl styrene) (PCMS) (PCMS-g-CuPc) to improve the compatibility between the filler and the polyurethane (PU) matrix. Then, two kinds of composite films (CuPc/PU and PCMS-g-CuPc/PU) were prepared using solution cast method, and subsequently, hot-pressed technology. TEM morphologies reveal that the distribution of PCMS-g-CuPc in PU matrix was improved and CuPc particles were coated by PCMS with an average size of ca. 25nm, about 20 times smaller than that of CuPc in CuPc/PU. Both of the improvements remarkably enhanced the interface exchange coupling effect. As a result, the PCMS-g-CuPc/PU composite with 15wt% CuPc can realize a dielectric constant of ca. 350 at 100Hz, about 7 times larger than that of CuPc/PU, and the dielectric loss is relatively low. The dielectric constant enhancement of the hot-pressed films can be attributed to the elimination of the matrix deposition layer formed during the solution cast method and the homogeneous distribution of PCMS-g-CuPc in PU matrix. In order to further enhance the dielectric properties of the composites, CuPc was directly graftedonto PU chains (PU-g-CuPc) and PU-g-CuPc/PU composite films were prepared using solution cast method. According to the TEM morphologies, CuPc particles dispersed in PU matrix better and the size of CuPc particles is in the range of 10~20nm, which should further reinforce the interface exchange coupling effect. The dielectric constant of PU-g-CuPc/PU composite with 15wt% CuPc is ca. 440 at 100Hz, which is 8 times higher than that of CuPc/PU.