Coassembly of nucleating agents in polymeric media

Overview & Synopsis

Nucleation of semi-crystalline polymers, and in particular polypropylene, is an effective industrial strategy to control thermal, mechanical and optical properties and to shorten the compounding cycle. The design of nucleating agents remains industrially key to achieve desirable properties, such as toughness and optical clarity. The most cost-effective nucleating agents are low molecular weight organic molecules that form supramolecular self-assemblies in the polymer melt, which provide a heterogeneous surface that is favorable for the polymer to undergo epitaxial crystallization. Nevertheless, the design of nucleating agents is largely based on empirical relationships. In this study, we aimed to address this gap by exploring coassemblies of nucleating agents. We developed a complete methodology of analysis allowing a deep understanding of supramolecular systems in molten polymeric media. For this purpose, two nucleating agents were selected on the basis of their selectivity for different PP morphisms. Their assembly and structure were analyzed by spectrocopic, microscopic, calorimetric, and X-ray diffraction methods. We then proceeded to study the formation of the coassembled nucleating agents using the same set of techniques. Fitting and modeling of experimental measurements acquired at thermodynamic equilibrium allowed us to access the thermodynamic parameters of our system, which ultimately gave us insight into the nature of the hetero-interactions at a molecular level. This theoretical study revealed the microstructure of the obtained copolymers. We used this information to rationalize the structure-properties relationship of between nucleating agent structure and polypropylene crystallinity. Finally, inspired by this approach, we began to design and prepare a new model system that would allow us to understand these self-assembly processes at polymer-polymer interfaces.