Ep14 solubility parameters and gel permeation chromatography - UC San Diego - NANO 134 Darren Lipomi

The script begins with a discussion on concluding topics in thermodynamics, focusing on ways to encourage polymer mixing through similarity or complementarity. It explains that polymers can mix if they have similar or complementary intermolecular forces, which can be achieved by altering the molecular structure or through ionic interactions. The concept of 'like dissolves like' is also discussed, highlighting the phase behavior of polymer systems and the role of entropy and enthalpy in mixing.

The second paragraph delves into the Hildebrand solubility parameters, which are used to predict the solubility of solvents and polymers based on the energy of vaporization. It explains the concept of cohesive energy density and how it relates to the solubility parameter. The script also touches on the relationship between the enthalpy of mixing and the solubility parameters of the components involved, emphasizing its utility for nonpolar media.

This section provides examples of solubility parameters for different polymers, such as polytetrafluoroethylene (PTFE), polystyrene, and nylon 6-6. It discusses the impact of molecular structure on the solubility parameter, with fluorine's electronegativity in PTFE leading to a low parameter value. The paragraph also covers how to calculate solubility parameters using empirical approaches and the limitations of this method for very polar materials.

The script explains the empirical method for calculating solubility parameters, using PMMA (poly methyl methacrylate) as an example. It breaks down the calculation into components based on the different groups present in the polymer, such as CH3 and CH2 groups, and how these contribute to the overall solubility parameter. The importance of understanding the hydrodynamic volume and the impact of solvent quality on polymer size is also highlighted.

The fifth paragraph introduces ring-opening metathesis polymerisation (ROMP), a process used to create polymers with double bonds in their backbone. It describes the mechanism of ROMP, where a metal catalyst is used to break and reform double bonds, leading to the formation of polymers. The paragraph also mentions the significance of ROMP in drug discovery and small molecule manufacturing, and its connection to the Nobel Prize in 2005.

This section discusses the method of size exclusion chromatography (SEC), also known as gel permeation chromatography (GPC), for determining the size of polymer chains. It explains the process of SEC, where a polymer sample is passed through a column filled with gel beads of varying pore sizes. Larger polymer chains are excluded from the pores and exit the column first, while smaller chains enter the pores and exit later, allowing for size-based separation.

The script continues to elaborate on the SEC mechanism, emphasizing that separation is based on hydrodynamic volume rather than molecular weight. It discusses the importance of calibrating the SEC system with chemically similar standards, such as polystyrene, and the challenges faced when dealing with polymers that lack suitable standards, like semiconducting polymers.

The final paragraph focuses on the retention time and volume in SEC, which are initially indicative of molecular weight but require calibration with known standards for accuracy. It explains that high molecular weight polymers have smaller retention times and volumes, while low molecular weight polymers have larger ones. The script also addresses the limitations of using polystyrene as a standard for polymers with different chemical properties.