Ultrasonic measurements of photo-crosslinked unsaturated polyether urethane copolymers

Photo-crosslinking of unsaturated methacrylic side groups attached to copol ymers of polyether urethane in the presence of benzoin methyl ether as phot olabile initiator had been investigated. Longitudinal ultrasonic attenuatio n in the solid form of these materials has been measured at 2, 4, 6, and 8 MHz in the temperature range 240-360 degrees K before and after the photo-c rosslinking process and in combination with difunctional acrylate ester mon omer. The occurance of crosslinking and the presence of secondary relaxatio n process beta -relaxation was confirmed. The activation energies, as well as the relaxation frequencies have been obtained. Elastic moduli in these m aterials were calculated and related to the composition before and after cr osslinking as well as to the difunctional acrylate ester monomer.