Search

A kinetic Monte Carlo model of polyurethane polymerization which explicitly tracks the polymer sequences is developed and shared. This model is benchmarked against theoretical and experimental polyurethane data and used to investigate the effect on oligomer distributions of unequal reactivity of the first and second isocyanate to react. The reverse reactions using thermodynamic consistency are then added to the framework, and analogous to the addition polymerization concept of ceiling temperature, equilibrium chain length distributions at various temperatures are calculated. For a mixture of three monomers AA, BB, and CC, where BB and CC do not react with one another, are present in stoichiometric proportions, and have different enthalpies of reaction with AA, an odd‐even effect emerges. Odd length chains are more likely than even length chains for temperatures at which BB and CC have significantly different equilibrium conversions. The concept of ceiling temperature that is typically cited for addition polymers is extended here to provide a measure of conditions under which depolymerization for recycling is favored. [ABSTRACT FROM AUTHOR]

The crosspropagation of 1-ethylcyclopentyl methacrylate (ECPMA) and methyl methacrylate (MMA) has been studied using a combination of quantum chemistry calculations and experiment. Our computational work utilizes a trimer-to-tetramer reaction model, coupled with an ONIOM (B3LYP/6-31G(2df,p): B3LYP/6-31G(d)) method for geometry optimization and an M06-2X/6-311+G(2df,p) method plus SMD solvation model for single point energy calculations. The results show several trends: the identity of the ultimate unit of a trimer radical affects not only the preferred conformation of the region where the reaction takes place, but also the reactivity of the radical; the addition of an ECPMA monomer to the radicals is generally favored compared to an MMA monomer; the pen-penultimate unit of a trimer radical shows a nonnegligible entropic effect; the penultimate unit effect is implicit for the ECPMA-MMA copolymer system. Finally, terminal model reactivity ratios fitted based on the explicit rate coefficients calculated from the quantum chemical results are compared with those from experimental measurements. The computations not only agree qualitatively with experimentally derived results in terms of the selectivity of ECPMA-MMA crosspropagation, but also give reasonable quantitative predictions of reactivity ratios. [ABSTRACT FROM AUTHOR]

It is challenging to track explicit copolymer sequences and related measures using continuum kinetic models. We developed a generalized framework based on kinetic Monte Carlo (KMC) to model free radical polymerization of any number of monomers to obtain the explicit sequence and its distribution. The KMC framework was applied to copolymerization of butyl acrylate/methyl methacrylate (BA/MMA) and methyl acrylate/methyl methacrylate (MA/MMA), and the simulation output was compared with experimental results. Sequence characteristics that were not accessible via experiments were then predicted. Explicit monomer sequence information was used to construct operating diagrams to design a representative copolymer recipe with a specific sequence target as a function of molecular weight and monomer conversion. [ABSTRACT FROM AUTHOR]

1,5-Hydrogen transfer reactions in methyl acrylate and butyl acrylate free-radical polymerization are studied using quantum chemistry and transition state theory to estimate the kinetic parameters ( ktr, Ea, and A) with tetrameric radicals, requiring a number of atoms that ranks among the largest polymeric mimics to date. A two-step transformation accounted for the overall reaction: rotation from an extended conformation to a coiled conformation and abstraction of the fifth hydrogen atom by the end-chain radical. UB3LYP/6-31G(d) was used for geometry optimization, validation of the transition states, and calculation of frequencies that were used to obtain thermodynamic properties. The more computationally demanding level of theory, MPWB1K/6-31G(d,p), was used for calculation of the electronic energy. [ABSTRACT FROM AUTHOR]