(429b) Computer-Aided Polymer Design Using COSMO-RS

COSMO-RS¹ is a successful and accurate statistical thermodynamics method that has distinct advantages for computer-aided molecular design (CAMD)²: (1) it incorporates QM-derived electronic and structural information; (2) thermodynamic property estimation of fluids is extremely fast assuming that a unique surface charge distribution called a sigma profile is known for each species in solution; and (3) COSMO-RS as a technique is amenable to integration with common CAMD strategies^3,4. However, CAMD using COSMO-RS is still a developing research area and has thus far typically focused on small molecule and solvent design. Addressing polymeric systems with COSMO-RS-based CAMD opens these powerful design techniques to diverse applications in membranes, electronics, aerospace materials, green chemistry, etc. Polymer design with COSMO-RS also benefits from the method’s accuracy in this domain as has recently been shown for a few properties⁵.

We address the optimization of polymers in this work with two primary strategies. The first leverages the simplicity of calculating the sigma profiles of polymeric structures from monomeric sub-units⁵. This strategy naturally leads to a mixed-integer nonlinear programming (MINLP) formulation which allows for the design of a copolymer from a large number of monomeric candidates. As a second strategy, we project the high-dimensional search space of polymeric structures into a lower dimensional space of the sigma moments (the statistical moments of the sigma profiles). This allows for the use of state-of-the-art derivative-free optimization (DFO) algorithms to address the design problem in a meaningful lower-dimensional space, for which they have been shown to be effective at finding good solutions in CAMD problems³. Because this strategy designs structures at each iteration, we also discuss the possibility of using molecular dynamics (MD) simulations for each designed system to improve the accuracy of the property estimates. We apply the methods to a few case studies drawn from the polymer literature.

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3. Austin ND, Sahinidis NV, Trahan DW. A COSMO-based approach to computer-aided mixture design. Chemical Engineering Science. 2017 Feb 23;159:93-105.
4. Scheffczyk J, Fleitmann L, Schwarz A, Lampe M, Bardow A, Leonhard K. COSMO-CAMD: A framework for optimization-based computer-aided molecular design using COSMO-RS. Chemical Engineering Science. 2017 Feb 23;159:84-92.
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