Bulk and suspension polymerization of vinyl chloride: the two-phase model

Talamini, G.; Visentini, A.; Kerr, J.

doi:10.1016/s0032-3861(97)00254-1

Cited by 19 publications

(22 citation statements)

References 25 publications

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“…51 According to Ravey et al 52 the polymer-rich phase is (2), and the propagation (3) reactions of the model vinyl chloride propagating radical (4). Also shown are the geometries of the corresponding vinyl chloride "polymer" (5), the radical product (6) of the 1-2 hydrogen shifts, vinyl chloride monomer (7), chloroallylic end group (8), and the addition of the propagating PVC radical to the double bond of the chloroallylic end group (9).…”

Section: Scheme 8 Model Reactions Used In the Calculation Of The Ratmentioning

confidence: 99%

New Insight into the Formation of Structural Defects in Poly(Vinyl Chloride)

et al. 2005

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The monomer conversion dependence of the formation of the various types of defect structures in radical suspension polymerization of vinyl chloride was examined via both 1H and 13C NMR spectrometry. The rate coefficients for model propagation and intra- and intermolecular hydrogen abstraction reactions were obtained via high-level ab initio molecular orbital calculations. An enormous increase in the formation of both branched and internal unsaturated structures was observed at conversions above 85%, and this is mirrored by a sudden decrease in stability of the resulting PVC polymer. Above this threshold-conversion, the monomer is depleted from the polymer-rich phase, and the propagation rate is thus substantially reduced, thereby allowing the chain-transfer processes to compete more effectively. In contrast to the other defects, the chloroallylic end groups were found to decrease at high conversions. On the basis of the theoretical and experimental data obtained in this study, this decrease was attributed to copolymerization and abstraction reactions that are expected to be favored at high monomer conversions. Finally, a surprising increase in the concentration of the methyl branches was reported. Although a definitive explanation for this behavior is yet to be obtained, the involvement of transfer reactions of an intra- or intermolecular nature seems likely, and (in the latter case) these could lead to the presence of tertiary chlorine in these defects.

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Section: Scheme 8 Model Reactions Used In the Calculation Of The Ratmentioning

confidence: 99%

New Insight into the Formation of Structural Defects in Poly(Vinyl Chloride)

et al. 2005

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“…[14][15][16]18,20 Therefore, the observed rate coefficients (also called apparent rate coefficients) of the monomolecular reactions in the polymer-rich phase and all the reactions in the monomerrich phase are considered to be related to the chemical reaction only and are equal to the intrinsic rate coefficients. The observed rate coefficients of bimolecular reactions in the polymer-rich phase are regarded as the sum of a reactionrelated term and a diffusion-related term and are calculated as follows: 20,38…”

Section: Combination Of Reaction and Diffusionmentioning

confidence: 99%

“…For reactions [13][14][15][16][17][18][19] in Table 4, rate coefficients have been obtained based on ab initio calculations reported by Purmova et al 10 and Van Cauter et al 24 The ab initio calculated values were taken as initial guesses and adjusted to obtain a good fit to the experimental data reported by Purmova et al 9 The pre-exponential factors of the hydrogen abstraction reactions are taken from Kiparissides et al 16 …”

Section: Combination Of Reaction and Diffusionmentioning

confidence: 99%

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Microkinetic Modeling of Structural Properties of Poly(vinyl chloride)

2009

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The free radical suspension polymerization of vinyl chloride is modeled at the elementary reaction level, systematically taking into account diffusion limitations. By deriving balances for structurally distinct polymer and radical species the formation of structural defects can be followed: monomer conversion, averages of the molar mass distribution and the structural defects content can be calculated as a function of polymerization time for industrially relevant conditions. A good agreement between literature reported and calculated values for these properties is obtained for a polymerization temperature range of 325-340 K, a dicetyl peroxydicarbonate and dimyristyl peroxydicarbonate initiator concentration range of 0.00069-1.0 wt %, and a monomer conversion range of 12-96%. The increase of the branching content and the decrease of the terminal double bond content at high monomer conversions can be explained in terms of a favoring of monomolecular reactions and the increasing importance of addition reactions to unsaturations at these conditions.

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“…The above physical assumption known as the two -phase model was proposed forty years ago by Talamini [2] and reviewed more recently by the same author [3] in the light of experience accumulated. With different modifi cations this model has been used in numerous studies issued from academia, but has proved to be a good support also for describing the behavior of real industrial systems.…”

Section: Kinetics Of Polymerizationmentioning

confidence: 99%