Steven G. Arturo

Systematic Method for Thermomechanically Consistent Coarse-Graining: A Universal Model for Methacrylate-Based Polymers.

We present a versatile systematic two-bead-per-monomer coarse-grain modeling strategy for simulating the thermomechanical behavior of methacrylate polymers at length and time scales far exceeding atomistic simulations. We establish generic bonded interaction parameters via Boltzmann inversion of probability distributions obtained from the common coarse-grain bead center locations of five different methacrylate polymers. Distinguishing features of each monomer side-chain group are captured using Lennard-Jones nonbonded potentials with parameters specified to match the density and glass-transition temperature values obtained from all-atomistic simulations. The developed force field is validated using Flory-Fox scaling relationships, self-diffusion coefficients of monomers, and modulus of elasticity for p(MMA). Our approach establishes a transferable, efficient, and accurate scale-bridging strategy for investigating the thermomechanics of copolymers, polymer blends, and nanocomposites.

Assessment of a Cost-Effective Approach to the Calculation of Kinetic and Thermodynamic Properties of Methyl Methacrylate Homopolymerization: A Comprehensive Theoretical Study.

In this work, we carried out a comprehensive density functional theory (DFT) study on the basis of a trimer-to-tetramer radical reaction model to assess a cost-effective approach to perform the calculation of kinetic and thermodynamic properties of methyl methacrylate (MMA) free-radical homopolymerization. By comparing results from several different functionals (PBE, M06-2X, wB97XD, KMLYP, and MPW1B95), in conjunction with a series of basis sets (6-31G(d,p), 6-31+G(d,p), 6-31G(2df,p), 6-311G(d,p), 6-311+G(d,p), 6-311+G(2df,p), 6-311+G(2df,2p)), we show that calculations using M06-2X/6-311+G(2df,p)//B3LYP/6-31G(2df,p) provide an activation energy of 5.25 kcal mol(-1) for the homopropagation step, which is within 1 kcal mol(-1) of the experimental value. However, this method predicts a heat of polymerization of 17.37 kcal mol(-1) that is larger than the experimental value by 3.5 kcal mol(-1). MPW1B95/6-311+G(2df,p) on the B3LYP/6-31G(2df,p) geometries produces a heat of polymerization value within 1 kcal mol(-1) of experimental data, yet overestimates the activation energy by 3 kcal mol(-1). In addition, we evaluated the performance of ONIOM MO:MO calculations on the geometry optimization of species comprising our MMA polymerization model and found that ONIOM(B3LYP/6-31G(2df,p):B3LYP/6-31G(d)) is capable of producing geometries in very good agreement with the full B3LYP/6-31G(2df,p) calculations. Subsequent calculations of energies using M06-2X/6-311+G(2df,p) based on the ONIOM geometries provided an activation energy value comparable to that based on the full B3LYP/6-31G(2df,p) geometries.

Application and comparison of derivative-free optimization algorithms to control and optimize free radical polymerization simulated using the kinetic Monte Carlo method

Abstract The diversity of the potential arrangements of multiple monomers along the length of polymer chains and their impact on polymer properties spark interest in the design of polymer sequence characteristics for particular applications. Kinetic Monte Carlo (KMC) is a technique that can track the explicit arrangement of monomers in the polymer chains, yet it is difficult to integrate with conventional gradient-based optimization algorithms that are typically invoked to design polymer properties. In this work, we applied and compared derivative-free optimization algorithms to incorporate KMC simulations and find synthesis conditions for achieving property targets and minimizing reaction time, advancing our ability to carry out the design of polymer microstructures and control polymerization processes.