MICROACOUSTIC CHARACTERIZATION OF PHOTOPOLYMER CROSS-LINKAGE

Two complementary microacoustic methods, microechography and acoustic microscopy, have been used to characterize the cross-linkage in photop olymers. The mechanical properties have been investigated as a functio n of the exposition time to UV by microechography. Two series of photo sensitive layers of 38.1 and 50.8 mum thicknesses have been studied at a frequency of 200 MHz. The rapid evolution of the longitudinal wave velocity with the state of cross-linkage and the good agreement betwee n these results and the photocalorimetry studies prove that microechog raphy, a non-destructive technique, is well adapted to control the cro ss-linkage. Acoustic microscopy studies, performed at a frequency of 5 30 MHz, reveal the influence of the atmosphere in contact with the mon omer during exposure on the mechanical characteristics of the polymers . Microacoustic techniques appear to be quite complementary to microca lorimetry; the photocalorimetry allows us to study the cross-linkage d uring reaction, and the kinetic, the initiator efficiency and the micr oacoustic methods allow us to study the final material and possibly to reveal the local gradients.