A series of polystyrene (PS) and a small amount of ultra high molecular wei
ght (UHMW) PS blends have been prepared by using tetrahydrofuran (THF). Mat
rix PS has an M-w of 423,000 (M-w/M-n = 2.36) and UHMW-PS has either an M-w
, of 3,220,000 (M-w/M-n = 1.05) or 15,400,000 (M-w/M-n = 1.30) in the range
of concentration from 0 wt% to 1.5 wt%. The influence of a small amount of
UHMW on dynamic viscoelasticity was investigated. At the frequency lower t
han 0.001 rad/s, the enhancement of G' was observed by the incorporation of
a small amount of UHMW. And the degree of enhancement was in the order of
M-w of UHMW and its concentration. The measurement of uniaxial elongational
viscosity for the blends was performed and the effects of UHMW on strain-h
ardening properties were analyzed at equal strain-rate conditions. The conc
entration of UHMW where the strain-hardening becomes substantially stronger
was determined. To get more insight into the cause of enhancement of strai
n-hardening at a certain concentration, the damping function from step-shea
r stress relaxation was measured. The influence of a small amount of UHMW o
n the damping function was found to be small. It was interpreted, from time
- and strain-dependency points, that the enhancement of strain-hardening by
a small amount of UHMW was governed by the long relaxation time.