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A 3D Simulation Investigation of the Influence of Temperature Increases on the Accuracy of Propagation Rate Coefficients Determined by Pulsed-Laser Polymerization
- Nikitin, Anatoly N., Lacík, Igor, Hutchinson, Robin A.
- Macromolecules 2016 v.49 no.24 pp. 9320-9335
- molecular weight, polymerization, polymers, temperature profiles, vinyl acetate
- A numerical approach has been developed to capture the inhomogeneous and nonstationary processes of pulsed laser polymerization (PLP). The new simulation tool has been applied to systematically investigate how temperature gradients that develop in the sample cell influence the accuracy of propagation rate coefficients, kₚ, determined by the PLP-SEC method. Although the temperature in the center of the sample cell may increase more than 30 °C during pulsing of bulk vinyl acetate (VAc), this increase does not greatly influence the accuracy of kₚ determined from the cumulative polymer molar mass distribution (MMD), provided that overall conversion in the system is kept low. Simulations indicate that the dependence of kₚ on laser pulse repetition rate observed experimentally for VAc is not caused by nonisothermal gradients. However, the temperature increases cause a widening of the peaks in MMDs, a loss of the expected PLP structure, and a slight increase in kₚ values with the number of pulses applied. These observations are demonstrated experimentally for vinyl pivalate (VPi), with simulated MMDs in good agreement with those measured experimentally. The pulse repetition dependence of kₚ observed in the literature for VPi is verified, with the value determined at 30 °C, kₚ = 7270 L mol–¹ s–¹, also in good agreement with literature.