Depropagation Kinetics of Sterically Demanding Monomers: A Pulsed Laser Size Exclusion Chromatography Study

Abstract

Conventional pulsed laser polymerization coupled with size exclusion chromatography (PLP−SEC) as well as multipulse pulsed laser polymerization has been employed to study the depropagation kinetics of the sterically demanding 1,1-disubstituted monomers dicyclohexyl itaconate (DCHI), dibutyl itaconate (DBI), and dimethyl itaconate (DMI). The effective rate coefficient of propagation, kpeff, was determined in bulk and solution of cyclohexanone (DCHI) and N-methylformamide (DMI) for monomer concentrations between 1.5 < < 7.1 mol L-1 in the temperature range 0 < T < 90 °C. The resulting Arrhenius plots (i.e., ln kpeff vs 1/RT) displayed a significant curvature in the higher temperature regimes and were analyzed in their respective linear parts to yield the activation parameters of the forward reaction. In the temperature region where no depropagation was observed, the following set of Arrhenius parameters for kp were obtained for the bulk systems: DCHI (Ep = 26.5 kJ mol-1, ln Ap/L mol-1 s-1 = 11.5), DBI (Ep = 21.3 kJ mol-1, ln Ap/L mol-1 s-1 = 10.4), DMI (Ep = 27.8 kJ mol-1, ln Ap/L mol-1 s-1 = 13.5). In addition, the kpeff data were analyzed in the depropagation regime for DCHI, resulting in estimates for the associated enthalpy and entropy (ΔH = −53.5 kJ mol-1 and ΔS = −142.3 J mol-1 K-1) of polymerization. The value for the heat of polymerization was independently measured via on-line differential scanning calorimetry (DSC) as well (ΔH = −55.0 kJ mol-1). ΔH of DBI and DMI were also determined via DSC or are available in the literature (ΔH = −42.0 and −60.5 kJ mol-1). These numbers were used to determine the respective entropies of polymerization for both monomers (ΔS = −110 and −156 J mol-1 K-1) by a fitting procedure of the kpeff data. DBI polymerization displays significantly different activation parameters as well as thermodynamic properties in comparison with the corresponding DCHI and DMI polymerizations. With decreasing monomer concentration, it is increasingly more difficult to obtain well-structured molecular weight distributions. The DCHI system displayed a significant reduction in kpeff with increasing cyclohexanone concentration.

Depropagation Kinetics of Sterically Demanding Monomers: A Pulsed Laser Size Exclusion Chromatography Study

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