Depropagation kinetics of sterically demanding monomers: A pulsed laser size exclusion chromatography study
Szablan, Zachary, Stenzel, Martina H., Davis, Thomas P., Barner, Leonie, & Barner-Kowollik, Christopher (2005) Depropagation kinetics of sterically demanding monomers: A pulsed laser size exclusion chromatography study. Macromolecules, 38(14), pp. 5944-5954.
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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, k(p)(eff) was determined in bulk and solution of cyclohexanone (DCHI) and N-methylformamide (DMI) for monomer concentrations between 1.5 < c(M)(0) < 7.1 mol L-1 in the temperature range 0 < T < 90 degrees C. The resulting Arrhenius plots (i.e., In k(p)(eff) 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 k(p) were obtained for the bulk systems: DCHI (E-p 26.5 M mol(-1), In A(p)/L mol(-1) s(-1) = 11.5), DBI (E-p = 21.3 kJ mol(-1), In A(p)/L mol(-1) s(-1) = 10.4), DMI (E-p 27.8 kJ mol(-1), In A(p)/L mol(-1) s(-1) = 13.5). In addition, the k(p)(eff) data were analyzed in the depropagation regime for DCHI, resulting in estimates for the associated enthalpy and entropy (Delta H = -53.5 M mol(-1) and AS = -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 (Delta H = -55.0 kJ mol(-1)). Delta H of DBI and DMI were also determined via DSC or are available in the literature (Delta H = -42.0 and -60.5 M mol(-1)). These numbers were used to determine the respective entropies of polymerization for both monomers (Delta S = -110 and -156 J mol(-1) K-1) by a fitting procedure of the k(p)(eff) 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 k(p)(eff) with increasing cyclohexanone concentration.
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|Item Type:||Journal Article|
|Divisions:||Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > Institutes > Institute for Future Environments
Current > QUT Faculties and Divisions > Science & Engineering Faculty
|Copyright Owner:||Copyright 2005 American Chemical Society|
|Deposited On:||29 Jul 2016 01:38|
|Last Modified:||29 Jul 2016 01:39|
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