MOBILITY OF KNOTS IN POLYETHYLACRYLATE NETWORKS - FLUORESCENCE ANISOTROPY MEASUREMENTS

The steady state fluorescence anisotropy of the chromophore dialkylben zene, which constitutes the crosslinks of polyethylacrylate and polyme thylmethacrylate networks, has been investigated over a range of tempe ratures, from -20 to 80 degrees C. In polymethylmethacrylate networks the limit anisotropy of dialkylbenzene (r(0) = 0.198) and vinylphenyl side groups of the elastic chains (r(0) = 0.304) have been determined by applying a correction method (previously reported) to discount arti facts typical of front face excitation. In polyethylacrylate networks it was found that the mobility of knots does not change appreciably wi th temperature even 100 degrees C above the glass transition of the sy stem (about -10 degrees C). It was concluded that polymer dynamics tha t affect the mobility of knots is different of that determining the mo tions of the elastic chains.