(193af) An Atomistic Evaluation of the Compatibility and Plasticization Efficacy of Phthalates in Poly(vinyl chloride)

Plasticizers are widely used to improve the properties and processability of certain polymer materials, such as polyvinyl chloride (PVC), in the plastic industry. Phthalates are the most widely used plasticizers on the market. These compounds tend to migrate out of the host polymer owing to their lack of chemical bonding and poor thermodynamic affinity with the polymer matrix, which results in the deterioration of materials performance, environmental contamination, and even harm to human health. Increasing governmental regulation is driving the search for more green and stable alternatives. Industrial selection of plasticizers largely relies on semi-empirical rules and even for successful candidates, it is often difficult to answer why they outperform other molecules in terms of effectively reducing the glass transition temperature and elastic modulus of the material. In this study, we build full-atom molecular models for the reliable prediction of plasticizer performance based on its chemical structure. A group of phthalates with similar molecular structure but different side chain configurations are simulated as test cases. Simulation results are in good agreement with experimental reports of their plasticization efficiency, thermodynamic compatibility, and migration resistance. Molecular insight from our simulation also helps us understand the fundamental relationship between plasticizer structure and its performance. This is the first step towards our eventual goal of developing a computational protocol for screening candidate plasticizers based on their chemical structures and finding high-performance and stable alternatives to phthalates. Beyond the PVC-plasticizer systems, we also note that chain length has a nontrivial effect on the cohesive energy and solubility parameter of long-chain polymers. This dependence will be discussed and should be an important consideration in the thermodynamic property prediction of polymers from molecular simulation.