Autoacceleration in Free Radical Polymerization. 1. Conversion

O’Shaughnessy, Ben; Yu, Jane

doi:10.1021/ma00096a032

Cited by 66 publications

(67 citation statements)

References 30 publications

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“…A constant k t dependent on the chain length would give a better result. For long chains, the termination would be smaller than for small active chains due to a restricted mobility [37][38][39][40][41][42], which leads to an increase of the mass molecular weight and the polydispersity.…”

Section: Resultsmentioning

confidence: 99%

Kinetic modeling of free radical polymerization of styrene initiated by the bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane

Cavin

2000

Polymer

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This paper deals with the kinetic study of bulk free radical polymerization of styrene initiated with the commercial bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane (Lupersol 256). The polymerization kinetics is investigated by DSC measurement for temperatures between 80 and 110ЊC and for initiator initial concentration from 0.115 up to 0.46 mol%. The experimental conversion and reaction rate are compared and discussed with the calculated values. For modeling the polymerization rate, a reaction scheme similar to the one given by Yoon and Choi (Polymer 1992;33(21):4582-4591) has been used and adapted. A detailed diffusional and semi-empirical model proposed by Chiu et al. (Macromolecules 1983;16(3):348-357) has been modified by Rouge (Etude de la polymérisation radicalaire du styrène initiée par un amorceur bifonctionnel dans un réacteur tubulaire à recyclage, Diploma work, DC, EPF, Lausanne, 1997) in order to describe these results. The model allows the description of the number molecular weight, but the polydispersity is underestimated for conversion higher than 70%. For temperature higher than 100ЊC, thermal initiation must be taken into account. The efficiency factor is found close to 1, but seems to decrease for temperatures above 100ЊC. ᭧

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Section: Resultsmentioning

confidence: 99%

Kinetic modeling of free radical polymerization of styrene initiated by the bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane

Cavin

2000

Polymer

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“…This gave credence to the general idea of ''short-long'' termination processes, [39,40] in which short radical chains control the termination reaction. [41] This picture postulates that during the gel-effect the termination of a long chain becomes so hindered due to diffusional limitations that it can only terminate when a ''short'' chain diffuses into its vicinity. As the population of ''short'' chains is presumably small, at this point the overall rate of termination decreases strongly.…”

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confidence: 99%

A Review of Modeling of Diffusion Controlled Polymerization Reactions

Achilias¹

2007

Macro Theory & Simulations

231

292

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A plethora of models have been developed quantifying the effect of diffusion‐controlled phenomena on polymerization reactions. The most prominent approaches are reviewed here, including innovative ones that have emerged over the last decade. Free‐radical and step‐growth polymerizations are considered in a way to show that similar models have been used in both mechanisms. In free‐radical polymerization the models proposed are subdivided according to their theoretical background into four categories: (i) based on a Fickian description of reactant diffusion; (ii) free‐volume theory based; (iii) chain‐length dependent; and, (iv) empirical. The reversible addition‐fragmentation technique is discussed, together with two industrially important case‐studies, solid state polycondensation and epoxy‐amine curing.magnified image

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“…We will see below how the predictions of the Flory-Schulz theory are modified 27 when one considers the dependence of k t on chain length at low conversions. At higher conversions, the Flory approximation becomes completely inadequate [33][34][35] as dead polymer accumulates in the polymerization mixture, slowing down the dynamics of reacting chains, and causing the famous autoacceleration phenomenon. 1 According to theory, the success of the Flory theory during low conversion FRP stems from a weak power law dependence of termination rate constant on chain lengths at low polymer concentrations.…”

Section: Flory-schulz Theory and Beyondmentioning

confidence: 99%

“…Now, to obtain the steady-state living MWD, let us consider the dynamics of living chains, which obey: 9,34,35 where ψ(N, t) is the number of living chains of length N units at time t, and H(N, t) is the "reaction field", i.e., the total reaction rate per chain of length N due to all other living chains in the system, given by…”

Section: Flory-schulz Theory and Beyondmentioning

confidence: 99%

Photocopying Living Chains. 1. Steady-State

et al. 2001

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We present the first ever measurements of living chain molecular weight distributions (MWDs), ψ o (N), in free radical polymerization (FRP), using a new technique, the "photocopy method". Though living chains are the fundamental objects in FRP, their MWDs have eluded measurement until now, principally due to their very short lifetimes (j1 s). In the photocopy method, the living population is converted, essentially instantaneously, to a labeled inert one by "photoinhibitor" molecules activated by a short laser pulse. This floods the FRP with photoinhibitor radicals, which ideally (i) are extremely slow to initiate new living chains yet (ii) couple with existing living chains (and each other) at near diffusion-controlled rates and (iii) carry a fluorescent label. Thus, the living chains are "frozen" and labeled. They are subsequently detected selectively using GPC equipped with a fluorescence detector (a second detector simultaneously detects unlabeled chains). We applied the photocopy method to low conversion methyl methacrylate FRP. Our measured MWDs are exponential as predicted by the classical FlorySchulz theory (which ignores the chain length dependence of the termination rate constant, k t), but only for chains longer than the mean living chain length N h o. For N < N h o, our data are consistent with a stretched exponential as predicted by modern FRP theories accounting for N dependence of kt. However, the small N data may also be accounted for by nonideal effects, initiation of new living chains by photoinhibitors, which lead to power law behavior. Another complication is that thermal initiation persists during the photocopying process in its present form. Thus, post-laser-pulse initiated living chains react with photoinhibitor radicals, distorting the measured MWDs from that of the steady-state living chains. From the measured living and dead MWDs, we infer living and dead chain concentrations and mean lengths and the fraction of living chains terminating via coupling. Finally, using reported values of propagation rate constants, we estimate mean living chain lifetime, polymerization rate, and the average termination rate constant.

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Autoacceleration in Free Radical Polymerization. 1. Conversion

Cited by 66 publications

References 30 publications

Kinetic modeling of free radical polymerization of styrene initiated by the bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane

Kinetic modeling of free radical polymerization of styrene initiated by the bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane

A Review of Modeling of Diffusion Controlled Polymerization Reactions

Photocopying Living Chains. 1. Steady-State

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