Solvent effects on free-radical copolymerization of styrene and 2-hydroxyethyl methacrylate: a DFT study

Abstract

The free-radical homopolymerization and copolymerization kinetics of styrene (ST) and 2-hydroxyethyl methacrylate (HEMA) in three different media (bulk, DMF, toluene) have been investigated by means of Density Functional Theory (DFT) calculations in combination with the Polarizable Continuum Model (PCM) and the Conductor-like Screening Model for Real Solvents (COSMO-RS). The conventional Transition State Theory (TST) is applied to calculate the rate parameters of polymerization. Calculated propagation rate constants are used to predict the monomer reactivity ratios, which are then used in the evaluation of the copolymer composition following the Mayo-Lewis equation. It is found that copolymerization reactions in bulk and toluene show similar transition geometries; whereas, DMF has a tendency to form H-bonding interactions with the polar HEMA molecules, thus decreasing the reactivity of this monomer during homopolymerization and towards ST during copolymerization. Calculations of copolymer composition furthershow that the amount of HEMA monomer in the ST-HEMA copolymer system decreases in the polar DMF solution. The calculated spin densities of the radical species are in agreement with the rate parameters and confirm that the copolymerization propagation rate of the ST-HEMA system is in the order: k p (bulk) E k p (toluene) > k p (DMF).

Polymerization Kinetics of Poly(2-Hydroxyethyl Methacrylate) Hydrogels and Nanocomposite Materials

“…This gives rise to a reduction in the polymerization rate compared to neat HEMA, more pronounced as the amount of nano-silica is increased. It should be noted here that similar results have been observed during polymerization of HEMA in polar solvents, such as DMF [28].…”

DFT Modeling of the Alternating Radical Copolymerization and Alder-Ene Reaction between Maleic Anhydride and Olefins

“…The reasons of the formation of alternate polymers by MA and olefins are still unclear in detail. The methods of quantum chemistry based on the density functional theory were successfully used for the analysis of different radical polymerization processes [50][51][52], including homo-and copolymerization of acrylates [53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71], acrylamides [70,72,73], and acrylonitrile [74]. However, as far as we know, DFT-based methods have not been extensively used for visualization and comprehensive analysis of the free radical alternating copolymerization of donor and cyclic acceptor monomers, except the publications of Matsumoto et al, devoted to the copolymerization of N-methylmaleimide (MMI) with olefins [75], and MA with 2,4-dimethylpenta-1,3-diene [76].…”

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

“…Aromatic compounds are capable of forming weak hydrogen bonds owing to their π electrons, with substitution by a methyl group increasing the donor ability of the ring [27]. It has been hypothesized that this reduces the electron density of the HEMA double bond and further enhances its reactivity, as suggested in a recent computational study [28]. However, it is unlikely that this effect is stronger than that introduced by intermolecular H-bonding between HEMA units.…”

“…While all studies relate the behavior to the hydroxyl functional group, the literature has been unable to reach a consensus on the cause of the increased reactivity. It has been hypothesized that a donor–acceptor complex between the growing polymer radical and the aromatic solvent affects reactivity [28,31], and that the non-polar solvent may lead to partial solubility that results in localization of the monomer species and preferential solvation [23,26] or to enhanced H-bonding involving HEMA units in the polymer chain [18]. As discussed for the copolymer composition results, perhaps all of these factors contribute to the behavior observed.…”