ECI Digital Archives

Title

A novel interpretation of measured and simulated PLP data

Authors

Yoshi W. Marien, Ghent University, Belgium
Paul H.M. Van Steenberge, Ghent University, Belgium
Gilles B. Desmet, Ghent University, Belgium
Marie-Françoise Reyniers, Ghent University, Belgium
Guy B. Marin, Ghent University, Belgium
Christopher Barner-Kowollik, School of Chemistry, Physics and Mechanical Engineering
Dagmar R. D’hooge, Laboratory for Chemical Technology and Centre for Textile Science and Engineering, Ghent University

Conference Dates

May 20-25, 2018

Abstract

Figure 1 - Simulated ν dependency of the observed k_p in vinyl acetate PLP at 323 K. Case 1 (♦): chain length independent head-to-tail prop., Case 2 (■): chain length dependent head-to-tail prop., Case 3 (●): chain length dependent head-to-tail, head-to-head, tail-to-tail, and tail-to-head prop., and Case 4 (▲): Case 3 with backbiting by head and tail radicals, and mid-chain prop.

Pulsed laser polymerization (PLP) is an interesting technique to study individual reactions.^1-4 In PLP, photoinitiator radical fragments are generated at laser pulses with a frequency ν (or dark time Δt = ν^-1). Depending on the PLP conditions and the monomer type, the molar mass distribution (MMD) can possess specific characteristics, allowing the determination of intrinsic rate coefficients. Most known is that under well-chosen conditions a multimodal MMD with inflection points L_j (j = 1, 2, …) is obtained, allowing the determination of the propagation rate coefficient k_p ([M]₀: initial monomer concentration):

(1)

In this contribution, kinetic Monte Carlo (kMC) modeling is applied to allow a further understanding and exploitation of PLP. For PLP of acrylates, regression analysis to low frequency inflection point data at various solvent volume fractions is proposed as an additional new method to estimate the backbiting rate coefficient k_bb.⁵ Moreover, it is demonstrated that photodissociation, chain initiation and termination reactivities can be extracted from the complete PLP MMD.⁶ For the first time, the ratio of MMD peak heights has been used for the fast and reliable estimation of the photodissociation quantum yield,Φ.⁷

For PLP of vinyl acetate a unique combination of ab initio calculated rate coefficients and kMC simulations is considered to explain the experimental⁸ ν dependency of the observed k_p (cf. Case 4 in Figure 1; Eq. (1) with k_p^obs). Via a stepwise extension of the kMC model (cf. 4 cases in Figure 1), the ν dependency is attributed to backbiting of tail radicals formed via head-to-head propagation.⁹ In contrast to acrylates, backbiting of head radicals is shown to be kinetically insignificant in VAc PLP, further highlighting the chemical difference between both vinyl monomer types.

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Recommended Citation

Yoshi W. Marien, Paul H.M. Van Steenberge, Gilles B. Desmet, Marie-Françoise Reyniers, Guy B. Marin, Christopher Barner-Kowollik, and Dagmar R. D’hooge, "A novel interpretation of measured and simulated PLP data" in "Polymer Reaction Engineering X (PRE 10) (2018)", John Tsavalas, University of New Hampshire, USA Fouad Teymour, Illinois Institute of Technology, USA Jeffrey Stubbs, HP Inc., USA Jose R. Leiza, University of the Basque Country, Spain Eds, ECI Symposium Series, (2018). https://dc.engconfintl.org/prex/50