Designing a polymer suitable for direct carbonization: the ReaxFF reactive approach

An atomistic view of the molecular changes characteristic for the carbonization were investigated using the ReaxFF molecular dynamics method, and further also analyzed using data science tools. To identify the structural characteristics of the polymers responsible for the promoting gas molecule production and development of all-carbon ring network we considered a range of polymers, differ in their backbone arrangement and type of the functional groups. Based on the quantitative measures, such as volatiles, carbon yield, all-carbon ring statistics, as well as connectivity of these rings, we determined some of the characteristics controlling a development of carbonous network, crucial for successful carbonization. We showed that a presence of 5-membered ring along the polymer backbone, especially furan, pyran ring and carbonyl groups, results in an evolution of high amount well connected 6-membered rings, whereas a presence of hydroxyl group or small number of heteroatoms leads to an opposite result. However, a presence of pyran/furan ring leads to a reduction in the carbon yield. Furthermore, to automatically infer the number of radical carbon for the considered systems, we also implemented a graph neural network using the Pytorch Geometric library. The evolution of reactive carbon was interpreted with the use of the Verhulst equation, where the fitting parameters were further examined as a possible useful tool in assessing the development of the carbonous network.