Elongational viscosity of multiarm (Pom-Pom) polystyrene

Jens Kromann Nielsen, Henrik K. Rasmussen, Kristoffer Almdal, Ole Hassager

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review


Two branched narrow molar mass distribution polystyrene melts have been synthesized: A multiarm A_nAA_n Pom-Pom polystyrene and AA_n asymmetric star polystyrene where n indicates the number of arms. The Pom-Pom and asymmetric star have molar masses 260 kg/mol and 255 kg/mol, respectively. The Pom-Pom was estimated to have 2.5 arms on average, while the estimate is 3.3 for the asymmetric star. The molar mass of each arm is about 27 kg/mol. The melts were characterized in the linear viscoelastic regime and in non-linear elongational rheometry. The transient elongational viscosity for the Pom-Pom molecule was found to be separable in time and strain for elongation rates larger than the inverse reptation time. Up to a Hencky strain of 2.7, the corresponding strain tensor component is closely approximated by a model that assumes the arms to be fully relaxed while the backbone is part of an unrelaxed entanglement network model. At Hencky strain above 2.7 a saturation of stress occurs that we interpret as withdrawal of the arms into the backbone tube. The observed strain associated with arm withdrawal is significantly larger than that predicted from an equilibrium force balance on the branch points while it corresponds well with an estimate of the maximum stretchability of the backbone. Time-strain separability was not observed for the 'Asymmetric star' molecule at the elongation rates investigated. The transient elongational viscosity for the 'Pom-Pom' molecule went through a reproducible maximum in the viscosity at the highest elongational rate.
Original languageEnglish
Title of host publicationThe Society of Rheology 78th Annual Meeting
Number of pages1
Place of PublicationMaine, USA
PublisherThe Society of Rheology
Publication date2006
Publication statusPublished - 2006
Event78th Annual Meeting of the Society of Rheology - Portland,ME, United States
Duration: 1 Jan 2006 → …
Conference number: 78


Conference78th Annual Meeting of the Society of Rheology
Country/TerritoryUnited States
Period01/01/2006 → …


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