The oscillatory flow birefringence properties (characterized by the magnitude Sm and relative phase angle θs of the complex mechanooptic coefficient S*) of solutions containing what were thought to be four-armed polystyrene stars (equal length arms linked with SiCl4) with narrow distribution number average molecular weights of 2.34 × 105 and 8.58 × 105 have been measured over a frequency range from 100 to 2 × 103 Hz at several temperatures. The solvent was Aroclor 1248, lot KM 502, a chlorinated biphenyl. The data have been extrapolated to obtain infinite dilution properties which are compared with the predictions of the Zimm-Kilb theory. The fits obtained indicate that the samples have substantial amounts of functionality polydispersity; the supposedly four-arm molecules apparently consist of a mixture of two-, three-, and four-armed structures, with the major component having three arms. Also, the values of the hydrodynamic interaction parameter required to generate theoretical fits to the data are essentially the same as those required to fit infinite dilution oscillatory flow birefringence and viscoelastic properties of linear polystyrenes in Aroclor solvents but are substantially different from those obtained for star polystyrene molecules from infinite dilution viscoelasticity studies. The precision obtainable with the oscillatory flow birefringence technique suggests that it may be a useful method for detecting small amounts of long-chain branching. © 1979, American Chemical Society. All rights reserved.
