Microacoustic characterization of photopolymer crosslinkage

Abstract Two complementary microacoustic methods, microechography and acoustic microscopy, have been used to characterize the cross-linkage in photopolymers. The mechanical properties have been investigated as a function of the exposition time to UV by microechography. Two series of photosensitive layers of 38.1 and 50.8 μm thickness 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 between these results and the photocalorimetry studies prove that microechography, a non-destructive technique, is well adapted to control the cross-linkage. Acoustic microscopy studies, performed at a frequency of 530 MHz, reveal the influence of the atmosphere in contact with the monomer during exposure on the mechanical characteristics of the polymers. Microacoustic techniques appear to be quite complementary to microcalorimetry; the photocalorimetry allows us to study the cross-linkage during reaction, and the kinetic, the initiator efficiency and the microacoustic methods allow us to study the final material and possibly to reveal the local gradients.