Tube dilation process in star‐branched cis ‐polyisoprenes

Tube theory of entangled polymer dynamics

“…Perhaps the most surprising and informative recent application of dielectric spectroscopy has been the case of entangled star polymers [188,189]. A`dynamic dilution' theory, in which the tube gradually dilates as entanglements are released by other stars in the neighbourhood [190], accounts for the rheological response with remarkable accuracy (see section 4.3.2 below).…”

“…The rheological relaxation spectrum itself is vastly broader for star polymer melts than linear chains. This is true of both rheological [85] and dielectric response [188]. As the molecular weight of the arms is increased, so the near-plateau of relaxation modes represented by G 00 …!…”

“…We might therefore expect it to be followed even more closely in star melts, if tube dilation is indeed rigorously true in that case. However, recent results indicate a departure from the tube dilation prediction for x¸2=3 [188] for Z armˆ8 . Increasing Z arm to 16 makes the picture even clearer (see data of ®gure 18).…”

Viscoelastic Relaxation of Linear Polyisoprenes: Examination of Constraint Release Mechanism

“…Therefore, a test of the CR feature is desired for polymers other than PS so that the CR model 2,3) can be refined on a rigid experimental basis. This test is desired in particular for cis-polyisoprenes (PI) for which molecular tests [15][16][17][18][19][20][21][22][23][24] of the entanglement dynamics have been recently made with the aid of the combination of the † To whom correspondence should be addressed.…”

“…8, we note that τ obs is longer than τ CR for these systems and the difference between τ obs and τ CR is enhanced time comparable with the reptation time thereby broadening the terminal mode distribution. 2,3) This broadening can be well described through the molecular picture of dynamic tube dilation, [17][18][19][20][21][22][23][24] a coarse-grained picture for the CR mechanism.…”