BACKGROUND: Selection of a polymer for two-phase partitioning bioreactor (TPPB) applications has previously been limited to heuristic approaches. However, recent interest has focused on first principles' selection methods based on polymer crystallinity, glass transition temperature and polymer-solute thermodynamic affinity. In this work, a framework is proposed to evaluate and predict polymer-solute thermodynamic affinity via the polymer-phase activity coefficient.

Solid imidazolium-based polyionic liquids (PILs; a class of polyelectrolyte) were synthesized for the absorption of n-butanol and other inhibitory biosynthesis products from dilute aqueous solutions.

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Two-phase partitioning bioreactor technology involves the use of a secondary immiscible phase to lower the concentration of cytotoxic solutes in the fermentation broth to subinhibitory levels. Although polymeric absorbents have attracted recent interest due to their low cost and biocompatibility, material selection requires the consideration of properties beyond those of small molecule absorbents (i.e., immiscible organic solvents). These include a polymer's (1) thermodynamic affinity for the target compound, (2) degree of crystallinity (wc ), and (3) glass transition temperature (Tg ). We have examined the capability of three thermodynamic models to predict the partition coefficient (PC) for n-butyric acid, a fermentation product, in 15 polymers. Whereas PC predictions for amorphous materials had an average absolute deviation (AAD) of ≥16%, predictions for semicrystalline polymers were less accurate (AAD ≥ 30%). Prediction errors were associated with uncertainties in determining the degree of crystallinity within a polymer and the effect of absorbed water on n-butyric acid partitioning. Further complications were found to arise for semicrystalline polymers, wherein strongly interacting solutes increased the polymer's absorptive capacity by actually dissolving the crystalline fraction. Finally, we determined that diffusion limitations may occur for polymers operating near their Tg , and that the Tg can be reduced by plasticization by water and/or solute. This study has demonstrated the impact of basic material properties that affects the performance of polymers as sequestering phases in TPPBs, and reflects the additional complexity of polymers that must be taken into account in material selection.

Imidazolium ionomer derivatives of an isobutylene-rich elastomer demonstrated superior absorption characteristics for target molecules of biological interest compared to their non-ionic parent material, while retaining biocompatibility with a range of suspended cell cultures.