| Abstract
| - Unique rheological properties of combined low melt viscosity and high melt elasticity arereported for a novel series of dendritically branched polystyrenes. Unlike previous studies, dendriticallybranched materials having different molecular weights but all possessing the same number of generationsare studied; this allows the determination of true scaling relationships. Zero shear viscosities scale withthe second power of molecular weight until corrected to a state of constant free volume, upon which theyscale with the first power of molecular weight. Importantly, the steady state shear compliance for thematerials increases with increasing molecular weight and is very large compared to other chainarchitectures. This finding holds potential technological importance as it may be possible to simultaneouslydecrease viscosity and increase elasticity by blending with these novel structures. Dynamic light scatteringand small-angle neutron scattering studies demonstrate the self-similar nature of these highly branchedpolymers, thereby establishing that the chain architecture is well-defined. Evidence of entanglements ismissing. Remarkably, this implies that it is possible to prepare unentangled polystyrenes having amolecular weight in excess of 1 000 000 (g/mol). Melt dynamics are complex; exhibited behaviorencompasses aspects of both classical Rouse−Zimm response and the power-law behavior associated withfractal or gelling systems. Neither Rouse−Zimm nor power-law relaxation time distributions are capableof quantitatively describing the data. However, the corrected viscosity scaling and the viscosity shearthinning behavior are in rough agreement with a theory of polymeric fractals proposed by Muthukumar[J. Chem. Phys. 1985, 83, 3161].
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