Predicting miscibility in polymer blends using the Bagley plot: Blends with poly (ethylene oxide)

Polymer blending is an interesting approach for developing new polymeric materials with unique properties. However, polymer blends are mostly immiscible. In fact, miscible polymers are in most cases considered as exceptional cases owing to the general rule of polymer immiscibility. Above all, investigating miscibility of polymers is quite difficult in a practical sense. Such difficulties emanate from high viscosity of the species, which tend to cause thermal degradation during processing, and low diffusion towards equilibrium.

Spanish researchers led by professor Emilio Meaurio at the university of the Basque Country obtained Bagley miscibility maps of polymer blends with poly(ethylene oxide) using current group contribution methods. The calculated solubility parameters were graphed in a Bagley plot and were used to inquire miscibility regions through comparison with the experimental results obtained from miscibility analyses. Their work is published in peer-reviewed journal, polymer.

The authors built Bagley plots for poly(ethylene oxide) blends by applying solubility parameters computed according to the group contribution methods developed by Hoftyzer-Van Krevelen, Hoy and Stefanis-Panayiotou. They also used the Yamamoto-Molecular Break (Y-MB) method implemented in the Hansen Solubility Parameters in Practice (HSPiP) software, which creates automatically first-order UNIFAC functional groups and applies an adaptive Neural Network methodology to account for inter-group interactions. They selected the poly(ethylene oxide) blends owing to its miscibility with a good number of miscible and immiscible polymeric materials. This allowed them to have a good representation of its solubility map with the appropriate information. The authors also obtained an additional Bagley plot by applying the miscibility parameters from solubility tests.

The authors observed that the plot obtained from solubility parameters assuming the Hoftyzer-Van Krevelen group contribution method indicating that miscible systems create circular region of 2.5MPa^1/2 around poly(ethylene oxide). Poly(ethylene oxide) is considered a non auto-associated polymeric material with accessible and strong acceptor groups. Therefore, its radius can be expected to be larger when compared to other polymers. In case the counterpart polymers contain complementary groups, miscibility can be achieved at larger distances. Complementary groups can establish hydrogen bond interactions with the ether groups of poly(ethylene oxide).

The authors realized that the Bagley plot from the parameters of the Hoy method had an expected behavior as most points followed a curvilinear trend. The total solubility parameters from this group contribution method were reliable, but the procedure to obtain the partial components was questionable. The research team therefore resolved that developing a Bagley plot to test the miscibility of polymer blends using this group contribution method may not offer much advantage over using the total solubility parameters directly.

They were able to analyze in their work a Bagley plot developed using experimental miscibility parameters drawn from solvent testing analyses. Unfortunately, this was also unable to define the miscibility around poly(ethylene oxide). However, the solubility parameter approach offers a simple and useful route to analyzing polymer miscibility. The success of the authors was pegged at the correct implementation of the proposed method, specifically in determining the solubility parameters of the polymers involved in the blend.

This study explored comprehensively the methods available for the application of the solubility parameters approach in a bid to predict the miscibility of polymer-polymer blends using blends with poly(ethylene oxide). The cloud of points obtained helped them to draw conclusions about coherent as well as the accuracy of every method used to obtain the miscibility parameters.

This paper analyzes the current procedures to predict polymer miscibility based on the solubility parameter approach.