Density Functional Theory Study of Free-Radical Polymerization of Acrylates and Methacrylates:  Structure−Reactivity Relationship

Abstract

Radical polymerization processes occur through a complex network of many different reactions. It is well-known that the polymerization rate is directly related to the monomer structure. The experimental polymerizability behavior is expressed as k p /k t 1/2 , where k p is the rate coefficient of propagation and k t is the rate coefficient of termination. In this study, the reactivity of a series of acrylates and methacrylates is modeled in order to understand the effect of the pendant group size, the polarity of a pendant group, and the nature of the pendant group (linear vs cyclic) on their polymerizability. The geometries and frequencies are calculated with the B3LYP/6-31+G(d) methodology whereas the energetics and kinetics of these monomers have been studied using the two-component BMK/6-311+G(3df,2p)//B3LYP/6-31+G(d) level of theory. For rotations about forming/ breaking bonds in the transition state, an uncoupled scheme for internal rotations has been applied with potentials determined at the B3LYP/6-31+G(d) level. Generally the rate constants for propagation k p mimic the qualitative polymerization trend of the monomers modeled and can be used with confidence in predicting the polymerizability behavior of acrylates. However in the case of 2-dimethylaminoethyl acrylate, chain transfer is found to play a major role in inhibiting the polymerization. On the other hand, the disproportionation reaction turns out to be too slow to be taken into consideration as a termination reaction.

A Perfect Couple: PLP/SEC/ESI‐MS for the Accurate Determination of Propagation Rate Coefficients in Free Radical Polymerization

“…These results are consistent with ab initio calculations that predict that both, the chain length dependence of k p and its dependence on the size of the ester chain are mainly an effect of the frequency factor, A being affected due to changes in the partition functions of the internal rotations of the propagation polymer chain. [19,[21][22][23][24] The activation energy depends mainly on electronic stabilization of the propagating radical and steric hindrance around the radical centre. E A is therefore expected to vary only by 1-2 kJ Á mol À1 with ester chain length.…”

“…Significant discrepancies in the Arrhenius parameters, A and E A , determined by a number of different research groups are found in the past literature, leading to inconsistencies between the conclusions of the individual authors [14][15][16][17][18] and also with theoretical predictions. [19][20][21][22][23][24] To address this problem, Zammit et al performed a comparison of the different calibration techniques in PLP/SEC of a number of poly(alkyl acrylates). These authors stated that -if MHKS parameters were accurately determined preferably using online multi-detection SEC -universal calibration was not the major cause of the observed inter-laboratory discrepancies in k p .…”

On the Use of Quantum Chemistry for the Determination of Propagation, Copolymerization, and Secondary Reaction Kinetics in Free Radical Polymerization

“…Intermolecular hydrogen abstractions like chain transfer to monomer and chain transfer to polymer were studied in various systems [106,[137][138][139][140][141]. Intramolecular hydrogen abstractions were investigated as well, focusing on the backbiting reactions that occur when a chain-end radical (CER) abstracts a hydrogen from its own backbone, forming a mid-chain radical (MCR) [70,106,[141][142][143][144].…”

Solvent Influence on Propagation Kinetics in Radical Polymerizations Studied by Pulsed Laser Initiated Polymerizations

“…In several studies it was suggested that the rate of the propagation reaction is largely governed by the relevant rotational modes of the transition state structure. [70][71][72][73][74] In the following text, some experimental aspects are briefly considered. In the main part experimental results are summarized and the origin of the solvent influence on homopolymerization k p is discussed, considering the results from theoretical studies.…”