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Influence of long-chain branching on time-pressure and time-temperature shift factors for polystyrene and polyethylene

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Abstract

Rheological characterizations were carried out for two polystyrenes. One was a linear polymer with M w =222,000 g/mol and M w /M n =2, while the other was a randomly branched polystyrene with M w =678,000 g/mol and a broad molecular weight distribution. Experiments performed included oscillatory shear to determine the storage and loss moduli as functions of frequency and temperature, viscosity as a function of shear rate and pressure, and multi-angle light scattering to determine the radius of gyration as a function of molecular weight. The presence of branching in one sample was clearly revealed by the radius of gyration and the low-frequency portion of the complex viscosity curve. Data are also shown for three polyethylene copolymers, one (LLDPE) made using a Ziegler catalyst and two made using metallocene catalysts, one (BmPE) with and one (LmPE) without long-chain branching (LCB). While the distribution of comonomer is known to be much more uniform in LmPE than in LLDPE, the pressure shift factors were the same for these two polymers. The pressure and temperature shift factors of the two polystyrenes were identical, but, in the case of polyethylene, the presence of a small amount of LCB in the BmPE had a definite effect on the shift factors. These observations are discussed in terms of the relative roles of free volume and thermal activation in the effects of temperature and pressure.

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Acknowledgements

We thank Dr. J. Kaschta for the GPC-data and Dr. J. Hepperle for providing the branched polystyrene.

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Authors and Affiliations

  1. Department of Chemical Engineering, McGill University, 3610 University Street, H3A 2B2, Montreal, Quebec, Canada

    Hee Eon Park & John Dealy

  2. Department of Materials Science, Institute of Polymer Materials, University Erlangen-Nürnberg, Martensstr. 7, 91058, Erlangen, Germany

    Helmut Münstedt

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  1. Hee Eon Park
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  2. John Dealy
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  3. Helmut Münstedt
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Correspondence to John Dealy.

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Park, H.E., Dealy, J. & Münstedt, H. Influence of long-chain branching on time-pressure and time-temperature shift factors for polystyrene and polyethylene. Rheol Acta 46, 153–159 (2006). https://doi.org/10.1007/s00397-006-0116-0

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  • DOI: https://doi.org/10.1007/s00397-006-0116-0

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