ULTRASONIC-DETECTION OF PHOTO CROSS-LINKING IN SOME ACRYLATE COPOLYMERS

The copolymerization of glycidyl methacrylate (GMA) with methyl methacrylate (MMA) at 65-degrees-C with 2,2'-azobisisobutyronitrile as radical initiator has been investigated. Monomer reactivity ratios for GMA and MMA are found to be r1 = 0.90 +/- 0.001 and r2 = 0.83 +/- 0.002, respectively. One of the copolymers obtained (GMA-MMA) containing 30% epoxide, was modified by reaction with acrylic acid. The polymerization of the unsaturated polyacrylic ester obtained has been photoinitiated in a solid state matrix. The ultrasonic pulse-echo technique was used, in the range of frequencies between 2.5 and 6 MHz and temperatures between 270 and 360 K, to detect the secondary relaxations in GMA-MMA. The activation energies for such relaxations were calculated and interpreted according to the flexibility of those unsaturated polyacrylate ester copolymers, both before and after exposure to ultraviolet irradiation, and also in the absence and presence of polyfunctional acrylate ester monomer.