(717d) Computer Aided Polymer Design Using Multiscale Modeling

Computer Aided Molecular Design (CAMD) is a technique that is finding increasing use in chemical product design. The goal of CAMD is to design (identify) chemical structures that meet a set of specified product criteria. This approach is substantial in the design of new products as it is cheaper and fasted than traditional synthesize-and-test paradigm. In CAMD solution steps, the property constraints are evaluated using a set of pre-selected predictive property models that use groups, atom-connectivity as well as molecular-descriptors to represent the generated molecular structures at different scales of size and structural details.

A multiscale modelling approach is necessary for design of polymer based products because it involves the design of the polymer repeat unit (at the macroscopic scale) and the arrangement of the repeat unit (at the microscopic scale). CAMD algorithm uses fragments to design the polymer repeat unit. Here, the fragments are the groups defined by Marrero/Gani (MG) and the property prediction models are based on MG group contribution approach. As there is a limitation on the availability of extensive experimental values of polymer properties, one cannot expect the entire group table without missing parameter entities. At times, there can be some polymer repeat unit structures, which cannot be totally represented by groups in the specified group contribution methods. A meso scale approach is therefore considered at this point where an atom-connectivity method is applied. The missing group and/or the missing group contributions for a property are determined automatically (without the need for additional experimental data) using the atom-connectivity models. The integration of group contribution and atom-connectivity index model is termed as the group contribution plus model (GC+) and these models, which have now been extended for the prediction of polymer repeat unit properties. These GC+ models have been implemented in the CAMD algorithm. A number of case studies have been done for identifying the repeat units, which promise to have the specified product criteria. A polymer design, however, cannot be confined to repeat unit identification. In reality, a polymer is not a single repeat unit or some repeat units arranged linearly, but it is a complex structure whose property can at times vary with the number of repeat units, the alignment of these repeat units, the branching frequency of the repeat units, etc.

Hence a micro scale approach need to taken for designing a polymer and to validate if it has the required property as promised by the identified repeat unit, obtained as an output from CAMD design, or not. In this approach, a long polymer chain is built using the identified repeat units in different ways and molecular dynamics simulations are carried out to either validate if the polymer has the required criteria or to calculate other properties which may not have GC+ property models. For example, free volume and diffusion of gases when the polymer product is to be used as sealant for some applications.

This presentation will highlight the multiscale modelling for design of polymers through a case study indicating the design of Polyisobutylene that can be used in many areas like biomedical, commercial, etc.