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

Abstract

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.

Understanding the regioselectivity of Michael addition reactions to asymmetric divinylic compounds

“…6, they can be arranged in an scis and s-trans conformation. Different authors [22][23][24] have studied the conformers of model monomers and their ndings suggest that all acrylic monomers, except MMA, are more stable in their cis conformation. For the particular case of the MMA monomer, long-range stabilizing interactions have been proposed as the origin of its preferential trans-conformation.…”

A Combined Computational and Experimental Study of Copolymerization Propagation Kinetics for 1‐Ethylcyclopentyl methacrylate and Methyl methacrylate

“…Consistent with our previous work on MMA homopropagation, we explored all possible conformers of reactants and TS originated from the s‐cis and s‐trans isomerization of a methacrylate monomer . In addition, we found that for ECPMA–MMA crosspropagation, another conformational consideration became important for the TS, which is the type of rotamer of the CC bond forming region, namely, anti and gauche, as depicted in Figure .…”

“…In the precedent work, we established a cost‐effective computational approach to calculate kinetic parameters describing MMA homopropagation . The predicted activation energy was in good agreement with the experimentally determined value.…”

“…The adopted ONIOM partition scheme is illustrated in Figure . This method has been shown to provide accurate geometries compared to conventional DFT calculations in our previous study on MMA homopolymerization . These optimized structures were then verified by vibrational frequency calculations at the same level of theory as the geometry optimizations, with reactants involving no imaginary frequencies and TS involving one imaginary frequency along the direction of bond formation.…”

“…On the basis of frequency calculations, zero‐point energies (ZPE) and free energy corrections were computed using scaled (0.9854) frequencies . Single point (SP) energy calculations were then carried out at the M06‐2X/6‐311+G(2df,p) level of theory, in order to identify the lowest free‐energy conformers of the reactants and TS and to obtain free energy changes (Δ G ≠ ) of propagation . SP calculations utilized an implicit solvation model on top of gas phase optimized structures to mimic the liquid phase environment that is typical of free‐radical polymerization.…”