Unveiling Solvent Effects on β-Scissions through Metadynamics and Mean Force Integration

This study introduces a methodology that combines accelerated molecular dynamics and mean force integration to investigate solvent effects on chemical reaction kinetics. The newly developed methodology is applied to the β-scission of butyl acrylate (BA) dimer in polar (water) and nonpolar (xylene and BA monomer) solvents. The results show that solvation in both polar and nonpolar environments reduces the free energy barrier of activation by ∼4 kcal/mol and decreases the pre-exponential factor 2-fold. Employing a hybrid quantum mechanics/molecular mechanics approach with explicit solvent modeling, we compute kinetic rate constants that better match experimental measurements compared to previous gas-phase calculations. This methodology presents promising potential for accurately predicting kinetic rate constants in liquid-phase polymerization and depolymerization processes.

Pulsed Laser Polymerization – Size Exclusion Chromatography Investigations into Backbiting in Ethylhexyl Acrylate Polymerization

Free radical acrylate polymerization is associated with a considerable number of side reactions occurring during chain growth. Most notably, the secondary chain propagating radicals can undergo intramolecular transfer reactions, forming...

Update and Critical Reanalysis of IUPAC Benchmark Propagation Rate Coefficient Data

We present an updated and expanded dataset of benchmark propagation rate coefficient (kp) data obtained from pulsed laser polymerization (PLP) of 13 vinyl monomers (styrene, methyl methacrylate, ethyl methacrylate, butyl...

A machine-readable online database for rate coefficients in radical polymerization

An online database created and curated by an IUPAC subcommittee is introduced.

When Mayo falls short (Ctr ≫ 1): the use of cumulative chain length distribution data in the determination of chain transfer constants (Ctr) for radical polymerizations

A method to determine chain transfer constants in free radical polymerizations that are >1 using molecular weight distribution data.

Critically evaluated propagation rate coefficients for radical polymerizations: acrylates and vinyl acetate in bulk (IUPAC Technical Report)

Arrhenius parameters capturing the temperature dependence of radical polymerization propagation rate coefficients, k p, for methyl acrylate, butyl acrylate, and vinyl acetate in bulk are reported, based on the fitting of benchmark data sets compiled from independent laboratories using the pulsed-laser polymerization/size exclusion chromatography method. The reported k p values for acrylates hold for secondary-radical propagation and are needed to calculate effective propagation rate coefficients in situations where there is a significant population of mid-chain acrylate radicals resulting from backbiting, as will be the case at technically relevant temperatures. The results are compared to those previously reported for styrene and methacrylates to highlight the large differences in k p values seen between the major monomer families.

Solvent Effects on Radical Copolymerization Kinetics of 2-Hydroxyethyl Methacrylate and Butyl Methacrylate

2-Hydroxyethyl methacrylate (HEMA) is an important component of many acrylic resins used in coatings formulations, as the functionality ensures that the chains participate in the cross-linking reactions required to form the final product. Hence, the knowledge of their radical copolymerization kinetic coefficients is vital for both process and recipe improvements. The pulsed laser polymerization (PLP) technique is paired with size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) to provide kinetic coefficients for the copolymerization of HEMA with butyl methacrylate (BMA) in various solvents. The choice of solvent has a significant impact on both copolymer composition and on the composition-averaged propagation rate coefficient (k_p,cop). Compared to the bulk system, both n-butanol and dimethylformamide reduce the relative reactivity of HEMA during copolymerization, while xylene as a solvent enhances HEMA reactivity. The magnitude of the solvent effect varies with monomer concentration, as shown by a systematic study of monomer/solvent mixtures containing 50 vol%, 20 vol%, and 10 vol% monomer. The observed behavior is related to the influence of hydrogen bonding on monomer reactivity, with the experimental results fit using the terminal model of radical copolymerization to provide estimates of reactivity ratios and k_p,HEMA.

From n-butyl acrylate Arrhenius parameters for backbiting and tertiary propagation to β-scission via stepwise pulsed laser polymerization

A stepwise method to estimate the Arrhenius parameters for backbiting, tertiary propagation, and β-scission in acrylate radical polymerization.

Ab initio based kinetic Monte Carlo analysis to unravel the propagation kinetics in vinyl acetate pulsed laser polymerization

The radical propagation kinetics of vinyl acetate in pulsed laser polymerization (PLP) is studied by combining ab initio calculated rate coefficients with kinetic Monte Carlo modeling of PLP spectra.