Kinetic features of radical polymerization occurring with auto-acceleration

SUMMARY: An approach for modeling chain-length dependent termination rate coefficients is presented. The method is based on the assumption that free-radical chain length may be considered as a continuous variable. As compared to discrete numerical methods, in continuous modeling the number of independent dimensionless parameters can be significantly reduced. As a consequence, for a wide variety of monomers the conversion dependence of k t can be predicted without extensive numerical calculations. The method may also be used to determine polymerization conditions under which simpler models of k t (which neglect effects arising from the dependence of k t on chain length) may be applied. Calculations for methyl methacrylate, styrene, and butyl acrylate bulk polymerizations up to high degrees of monomer conversion show that the impact of chain length on termination varies with conversion and strongly depends on the type of monomer.

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“…The data for MMA and styrene are from ref. 11,26,27) The BA data are from ref. According to the classification proposed in ref.…”

Section: Calculations and Discussionmentioning

confidence: 99%

“…The calculations that follow thus do not include the range of very high conversions (x F 0.8). The kinetic parameters for MMA, styrene 11,26,27) and BA 28,29) polymerizations are given in Tab. 1.…”

Section: Calculations and Discussionmentioning

confidence: 99%

Modeling termination kinetics in free-radical polymerization using a reduced number of parameters

Buback¹,

Egorov²,

Kaminsky³

1999

Macromol. Theory Simul.

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“…In this case the high density of the matrix network (4 times higher in comparison with theoretical one) impedes the outlet of radicals from the ''cage'' and diffusion may restrict not only the termination reaction but initiation. In [22] for polymerization of n-alkyl methacrylate it was shown that diminishing the termination constant is determined by lowering the free volume of the reaction media and by the appearance of topological entanglements leading to the formation of entanglement network. It was also established that by polymerization of styrene and MMA in beforehand prepared three-dimensional networks the termination constant is 3 orders lower as compared to bulk.…”

Section: Experimental Partmentioning

confidence: 99%

Effects of Confinement on the Kinetics of Formation of Sequential Semi‐Interpenetrating Polymer Networks

Alekseeva

Lipatov

Sorochinskaya

et al. 2007

Macromolecular Symposia

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Summary: Peculiarities of formation kinetics of sequential semi-interpenetrating polymer networks (semi-IPNs) based on crosslinked polyurethane (PU) with different cross-linking density and linear polystyrene (PS), polybutylmethacrylate (PBMA) and polymethacrylate acid (PMAA) have been studied. The experimental data show the dependence of the kinetic parameters of polymerization on M c , this dependence being different for various monomers. Sharp discrepancy in molecular mass distribution of polymers formed in various matrices has been observed. The differences in dependencies of reaction kinetics and molecular mass distribution are supposed to be connected to various dependence of the chain growth and termination of various monomers on the density of network, i.e. on the confinements imposed by the intranetwork space.

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“…9 These changes lead to diffusion control of the large polymeric radical chains and suppression of their translation through the reacting system, leading to autoacceleration. [10][11][12][13][14][15][16][17][18][19] The termination rate decreases with increasing polymer concentration, and radical recombination eventually occurs more rap-idly by a radical propagating through nearby vinyl groups until meeting and terminating with another radical. This latter termination regime is referred to as reaction diffusion-controlled termination.…”

Section: Introductionmentioning

confidence: 99%

“…At very low double bond conversions a gel of infinite molecular weight forms, which dramatically decreases the reacting species' mobility . These changes lead to diffusion control of the large polymeric radical chains and suppression of their translation through the reacting system, leading to autoacceleration. − The termination rate decreases with increasing polymer concentration, and radical recombination eventually occurs more rapidly by a radical propagating through nearby vinyl groups until meeting and terminating with another radical. This latter termination regime is referred to as reaction diffusion-controlled termination. − As the reacting species' mobility decreases further, the small monomer molecule also becomes diffusion-controlled and autodeceleration is observed.…”

Section: Introductionmentioning

confidence: 99%

A Modeling Investigation of Chain Length Dependent Termination during Multivinyl Free Radical Chain Photopolymerizations: Accounting for the Gel

Lovestead

Bowman

2005

Macromolecules

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A mathematical model of multivinyl monomer free radical photopolymerizations that takes into account chain length dependent termination (CLDT) and gel formation (an infinite network) was utilized to obtain a more accurate picture of network formation and multivinyl monomer photopolymerization kinetics. The model predicts an increased probability that a radical chain is attached to the gel with increasing chain length and double bond conversion. Accounting for CLDT delays radical incorporation into the gel and induces gel formation at earlier double bond conversions. Increasing the initiation rate also delays gel formation. When the model is expanded to account for the probability that a highly mobile sol radical reacts to become a nearly immobile gel radical, the importance of CLDT prior to reaction diffusion-controlled termination is increased. This result is attributed to bimolecular termination occurring between a short (<10-mer) sol radical and a long gel radical (short−long radical termination). The transition from a CLDT important regime to reaction diffusion-controlled termination is characterized by a transition from primarily short−long to primarily long−long (gel−gel) radical termination.

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Kinetic features of radical polymerization occurring with auto-acceleration

Cited by 5 publications

References 31 publications

Modeling termination kinetics in free-radical polymerization using a reduced number of parameters

Modeling termination kinetics in free-radical polymerization using a reduced number of parameters

Effects of Confinement on the Kinetics of Formation of Sequential Semi‐Interpenetrating Polymer Networks

A Modeling Investigation of Chain Length Dependent Termination during Multivinyl Free Radical Chain Photopolymerizations: Accounting for the Gel

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