Original Contribution

Rheologica Acta

, Volume 44, Issue 4, pp 342-351

First online:

A regularization-free method for the calculation of molecular weight distributions from dynamic moduli data

  • Job D. GuzmánAffiliated withDepartment of Chemical Engineering, Illinois Institute of TechnologyThe Dow Chemical Company
  • , Jay D. SchieberAffiliated withDepartment of Chemical Engineering, Illinois Institute of Technology Email author 
  • , Richard PollardAffiliated withThe Dow Chemical Company

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Abstract

There are several models for the determination of molecular weight distributions (MWDs) of linear, entangled, polymer melts via rheometry. Typically, however, models require a priori knowledge of the critical molecular weight, the plateau modulus, and parameters relating relaxation time and molecular weight (e.g., k and α in τ=kMα). Also, in an effort to obtain the most general MWD or to describe certain polymer relaxation mechanisms, models often rely on the inversion of integral equations via regularization. Here, the inversion of integral equations is avoided by using a simple double-reptation model and assuming that the MWD can be described by an analytic function. Moreover, by taking advantage of dimensionless variables and explicit analytic relations, we have developed an unambiguous and virtually parameter-free methodology for the determination of MWDs via rheometry. Unimodal MWDs have been determined using only a priori knowledge of the exponent α and dynamic moduli data. In addition, the uncertainty in rheological MWD determinations has been quantified, and it is shown that the reliability of the predictions is greater for the high-molecular-weight portion of the distribution.

Keywords

Molecular weight distribution Uncertainty Dynamic moduli