Ternary Solid–Liquid Equilibria of Semicrystalline, Branched Polymer Solvent Mixtures—A Theoretical Study by Means of Lattice Cluster Theory

et al. 2021

Ind. Eng. Chem. Res.

Self Cite

In this work, a thermodynamic model is developed based on continuous thermodynamics and lattice cluster theory to describe solid−liquid equilibria of polymer−solvent systems, where the polymer shows a certain molecular architecture, semicrystallinity, and a continuous molecular weight distribution. The new thermodynamic model is validated by predicting the solid− liquid phase behavior of ethylene/1-hexene copolymer−1,2,4-trichlorobenzene mixtures for different short-chain branchings, degrees of crystallinities, and molecular weight distributions. It turned out that this thermodynamic model is capable of capturing the solid− liquid transition zone, where a manifold of solid−liquid equilibria exists, due to the continuous character of the molecular weight distribution. For the first time, the coexistence region of the solid−liquid transition of a polyethylene−solvent system is predicted based on a thermodynamic consistent model. Further model calculations show how the polydisperse nature of the polymer influences the coexistence region in a complex and nonlinear manner, especially in the low-molecular-weight regime. This gives new insights into the solid−liquid phase behavior of polydisperse polymer−solvent mixtures and provides valuable information on the field of polymer crystallization.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermodynamic Modeling of the Solid–Liquid Phase Transition in Polyethylene Copolymer–Solvent Systems Based on Continuous Thermodynamics and Lattice Cluster Theory

Fan

Zeiner

et al. 2021

Ind. Eng. Chem. Res.

Self Cite

Impact of higher order diagrams on phase equilibrium calculations for small molecules using lattice cluster theory

Zimmermann

Walowski

The Journal of Chemical Physics

2018

The Lattice Cluster Theory (LCT) provides a powerful tool to predict thermodynamic properties of large molecules (e.g., polymers) of different molecular architectures. When the pure-component parameters of a certain compound have been derived by adjustment to experimental data and the number of atoms is held constant within the molecule so that only the architecture is changed, the LCT is capable of predicting the properties of isomers without further parameter adjustment just based on the incorporation of molecular architecture. Trying to predict the thermodynamic properties of smaller molecules, one might face some challenges, which are addressed in this contribution. After factoring out the mean field term of the partition function, the LCT poses an expression that involves corrections to the mean field depending on molecular architecture, resulting in the free energy formally being expressed as a double series expansion in lattice coordination number z and interaction energy ε̃. In the process of deriving all contributing sub-structures within a molecule, some parts have been neglected to this point due to the double series expansion being truncated after the order ε̃2z−2. We consider the neglected parts that are of the order z−3 and reformulate the expression for the free energy within the LCT to achieve a higher predictive capability of the theory when it comes to small isomers and compressible systems. The modified version was successfully applied for phase equilibrium calculations of binary mixtures composed of linear and branched alkanes.

Thermodynamic Principles for the Design of Polymers for Drug Formulations

Fischlschweiger

Annu. Rev. Chem. Biomol. Eng.

2019

Polymers play an essential role in drug formulation and production of medical devices, implants, and diagnostics. Following drug discovery, an appropriate formulation is selected to enable drug delivery. This task can be exceedingly challenging owing to the large number of potential delivery methods and formulation and process variables that can interact in complex ways. This evolving solubility challenge has inspired an increasing emphasis on the developability of drug candidates in early discovery as well as various advanced drug solubilization strategies. Among the latter, formulation approaches that lead to prolonged drug supersaturation to maximize the driving force for sustained intestinal absorption of an oral product, or to allow sufficient time for injection after reconstitution of a parenteral lyophile formulation, have attracted increasing interest. Although several kinetic and thermodynamic components are involved in stabilizing amorphous dispersions, it is generally assumed that maximum physical stability, defined in terms of inhibition of drug crystallization, requires that the drug and excipient remain intimately mixed. Phase separation of the drug from its excipient may be the first step that ultimately leads to crystallization. We discuss the role of advanced thermodynamics using two examples: ASD and vitamin E–stabilized ultrahigh–molecular weight polyethylene implants.