Dielectric properties of castor oil cross-linked polyurethane

A series of polyurethanes cross-linked with castor oil were synthesized and the influence of the polyurethane chemical structure on molecular relaxations in such systems was determined. Three different castor oil rates were used in the synthesis of the cross-linked polyurethane chains. These cross-linked polyurethanes were compared with a linear polyurethane which was obtained by chain extension with 1,4-butane diol. The dielectric properties and relaxation phenomena of the polyurethane were studied as a function of the hard segment structure and cross-linker content as structural variables and frequency and temperature as experimental variables. It was found that the formation of hydrogen bonds between urethane groups of physical networks may control the molecular mobility, but the chemical nature and content of the cross-links of the hard segments strongly influences the molecular relaxation. The relaxation peaks were observed in the temperature range of -65 to 60 degrees C for polyurethane with different cross-linked segment contents, peaks which shifted to high temperature with the increase in frequency.