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Entanglement Transition of Randomly Branched Polymers in the Hyperbranched Class

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posted on 19.09.2006, 00:00 by Suneel Kunamaneni, D. Martin A. Buzza, Daniel J. Read, David Parker, Alan M. Kenwright, W. James Feast, Anne L. Larsen
We study the melt rheology of randomly branched polymers in the hyperbranched polymer (HBP) class which are formed by the co-condensation of AB and AB2 type monomers. Specifically, we study the effect of branch length Mx on the entanglement transition in the HBP class. To this end, two series of HBPs were prepared using AB2 mole fractions of 10% and 1% respectively. This allowed us to vary Mx from just below to just above Me, the entanglement molecular weight for linear chains of the same chemistry. For the 10% branched samples (Mx < Me), we were able to quantitatively model the low and intermediate frequency rheology data using a Rouse model for unentangled chains. For the 1% branched samples (Mx > Me), there is a clear entanglement plateau for the higher molecular weight samples and we were able to quantitatively model the rheology around the entanglement plateau region using the tube model. Our data demonstrate conclusively that the entanglement transition for randomly branched polymers in the HBP class is controlled by Mx and the transition occurs around Mx Me. These conclusions are the same as for randomly branched polymers in the percolation class. We are able to explain these results using either the Colby−Rubinstein model or double reptation model for entanglements if we assume that whole molecules and side branches with Rouse times less than the Rouse time of an entanglement do not contribute to entanglement formation.