Rheology of Star-Branched Polyisobutylene

Abstract

The rheology of high molecular weight, six-arm-star polyisobutylenes (PIB) was measured and compared to the behavior of linear PIB. The polymers had equivalent plateau moduli and conformed well in the terminal zone to the time-temperature superposition principle. Moreover, the temperature coefficients of the terminal relaxation times were identical for the star and linear polymers. Since the trans and gauche conformations in PIB have virtually the same energy, this absence of enhanced temperature sensitivity in star PIB, as well as the thermorheological simplicity, is consistent with an interpretation of the rheology of branched polymers based on an arm retraction mechanism.

Effect of temperature on the terminal relaxation of branched polydimethysiloxane

“…2 is consistent with a lack of such enhancement in PDMS. Similar results were reported for PIB [19,20]. This correspondence between the effects of branching on the temperature dependence and on thermorheological complexity is predicted by models [8][9][10].…”

“…Thus, the arm retraction models predict thermorheological simplicity and no difference in temperature dependence between branched and linear chains. This is exactly what was found both for stars [19] and for arborescent combs [20]. PIB is unusual in this regard; well-entangled branches have usually been found to enhance the temperature dependence of the rheological properties.…”

Reentanglement Kinetics in Polyisobutylene

“…In this work we performed interrupted shear flow experiments on neat polyisobutylene (PIB). The molecular weight was five times the entanglement molecular weight of PIB (M e = 9400 Da 22 ), sufficiently high to yield stress overshoots but low enough that melt fracture and inhomogeneous flow could be avoided. We find that consistent with prior results on polymer solutions, the entanglement recovery time is significantly longer than the linear relaxation time; that is, partially disentangled chains recover their structure more slowly than expected from their equilibrium mobility, even though diffusion per se is faster for chains having fewer entanglements.…”

Filler Dispersion in Hyperbranched Polyisobutylene

“…The properties of the linear polymer have been studied by many techniques, including mechanical spectroscopy, [21][22][23][24] light scattering, 25 optical birefringence, 26,27 neutron scattering, 28,29 dielectric spectroscopy 29 and computer simulation. 30,31 A few studies of star-branched PIB have appeared, 32,33 while our recent interest has been the viscoelastic response of hyperbranched polyisobutylene. [34][35][36] Produced by carbocationic polymerization, these materials have a random, tree-like structure, 37 lacking the self-similarity of dendrimers.…”