The effect of deuteration on the ultrasonic properties of poly(methyl methacrylate)

Room-temperature ultrasonic compressional wave velocity and attenuation measurements have been carried out on commercial poly-methyl methacrylate (PMMA) and fully deuterated PMMA. Deuteration was found to reduce the velocity by 4.4 ± 1.2% which can be completely accounted for by the density change of 8.0%, assuming no changes in atomic force constants or molar volume. The attenuation was 17% higher in the deuterated sample. Making reasonable assumptions about the distribution function for the relaxation times of molecular groupings moving in two-well potentials, the attenuation increase is attributed to a reduction in the attempt frequency for barrier hopping of main chain and/or ester methyl groups.