ARM-LENGTH DEPENDENCE OF STRESS-RELAXATION IN STAR POLYMER MELTS

We apply our recent microscopic theory of stress relaxation in star po lymer melts to dynamic rheology data of Fetters et al. on melts of mon odisperse four-arm polyisoprene stars, with arm molecular weights in t he range 17 000 to 105 000 (M/M-e from 3.4 to 21.0, with M-e = 5000). The agreement between theory and experiment is excellent for all frequ encies and arm lengths, with physically reasonable values of plateau m odulus and friction factor and no other adjustable parameters. These d ata obey time-temperature superposition, with no evidence for anomalou s arm-length dependence of activation energies as seen in polyethylene -branched polymers.