Solvent Effects on Acrylate k_p in Organic Media?—A Systematic PLP–SEC Study

Abstract

The Arrhenius parameters of the propagation rate coefficient, kp , are determined employing high-frequency pulsed laser polymerization-size exclusion chromatography (PLP-SEC) for the homologous series of five linear alkyl acrylates (i.e., methyl acrylate (MA), butyl acrylate (BA), dodecyl acrylate (DA), stearyl acrylate (SA), and behenyl acrylate (BeA)) in 1 m solution in butyl acetate (BuAc) as well as in toluene. The comparison of the obtained kp values with the literature known values for bulk demonstrates that no significant solvent influence neither in BuAc nor in toluene on the propagation reaction compared to bulk is detectable. Concomitantly, the kp values in toluene and in BuAc solution display a similar increase with increasing number of C-atoms in the ester side chain as was previously reported for the bulk systems. These findings are in clear contrast to earlier studies, which report a decrease of kp with increasing ester side chain length in toluene. The additional investigation of the longest and shortest ester side chain acrylate (i.e., BeA and MA) over the entire experimentally available concentration range at one temperature (i.e., 50 °C) does not reveal any general concentration dependence and all observed differences in the kp are within the experimental error.

The influence of hydrogen bonding on radical chain-growth parameters for butyl methacrylate/2-hydroxyethyl acrylate solution copolymerization

“…19 In general acrylic non-aqueous solution (and bulk) polymerizations are not significantly dependent on solvent choice. 20,21 Small deviations from bulk propagation behavior can be explained in terms of differences in solvent and monomer molar volumes, 20,22 and the "fish in water" argumentation applied to weak interactions: solvent molecules replacing monomer molecules allow for a higher rotational freedom of the monomer, including intermolecular interactions based on changing dipole moments of the solvent. 23 For these types of systems, copolymerization reactivity ratios are generally independent of solvent choice, as no strong interactions are present.…”

Dependence of Propagation Rate Coefficients in Radical Polymerization on Solution Properties: A Quantitative Thermodynamic Interpretation

“…As another example, we would also like to contribute to a recent debate in the literature regarding acrylate systems. Haehnel et al performed a study on the k p of acrylates with ester groups of different size in bulk, toluene and butyl acetate, and concluded in favor of an absence of solvent effect. In contrast, a solvent effect was suggested by Buback based on the data from Couvreur et al To provide a theoretical perspective to this question, we have assumed that all monomer–solvent systems mentioned in these publications belong to Case 3 (or the trivial Case 1), for which R ≈ 1, and have estimated the corresponding value of via Equation .…”

“…Comparison of measured and computed values of for a series of acrylates with different ester groups in toluene. The experimental ratios were determined using the bulk values cited by the authors of the two PLP–SEC studies; neither study included own measurements in bulk.…”

No Apparent Correlation of kp with Steric Hindrance for Branched Acrylates

“…In fact, the opposite is observed, as the propagation behavior apparently exhibits no clear or striking correlation in bulk and in 1 m solution in BuAc, neither from one monomer to another, nor from bulk to solution. This is a surprising observation, since it is in clear contrast to the other monomer families: for the linear alkyl acrylates, for example, our group was able to demonstrate that there is no significant variation in ln( k p ) with differing monomer concentrations from bulk to the very dilute conditions …”

“…This is a surprising observation, since it is in clear contrast to the other monomer families: for the linear alkyl acrylates, for example, our group was able to demonstrate that there is no signifi cant variation in ln( k p ) with differing monomer concentrations from bulk to the very dilute conditions. [ 36 ]…”