Free radical concentration, during polymerization

In polymerization of styrene in benzene at 60°C using 0.1 mol benzoyl peroxide initiator and 1 mol of monomer, is 1.38 x 10, assume steady state and calculate the free-radical concentration during the reaction. If is 176/mol what is the rate of propagation What is the lifetime of a growing radical if k is 7.2 x 10 What is the rate of propagation if the initiator efficiency is 72% ... 

Various techniques have been studied to increase sohds content. Hydroxy-functional chain-transfer agents, such as 2-mercaptoethanol [60-24-2], C2HgOS, reduce the probabihty of nonfunctional or monofunctional molecules, permitting lower molecular-weight and functional monomer ratios (44). Making low viscosity acryhc resins by free-radical initiated polymerization requires the narrowest possible molecular-weight distribution. This requires carehil control of temperature, initiator concentration, and monomer concentrations during polymerization. 

This reaction is a termination and limits the molecular weight of the final molecule. In solution or melt polymerization the level of free radical concentration must for this reason not be raised over 10 to 10 M to 3deld reasonably high molecular weight (5). In case a ci3 tal surface would contain higher numbers of mobile free radicals, termination would be unavoidable. Also, crystal nucleation by active intermediate oligomers, as is observed in crystallization during step reaction polymerization, would most likely lead to termination. 

The equation for the rate of propagation, shown above, contains the term [M ]. It designates radical concentration. This quantity is difficult to determine quantitatively, because it is usually very low. A steady state assumption is therefore made to simplify the calculations. It is assumed that while the radical concentration increases at the very start of the reaction it reaches a constant value almost instantly. This value is maintained from then on and the rate of change of free-radical concentration is assumed to quickly become and remain zero during the polymerization. At steady state the rates of initiation and termination are equal, or Ri = R i=2Xi[M ]. It is possible to solve for [M ], which can then be expressed as ... 

The maximum free radical concentration [R+ ] is reached immediately after the laser pulse has been applied. It is the sum of the radical concentration formed at each laser flash, p, and the amoimt of free radicals still in the system, which are prodnced by former pnlses, [R ]. This value is identical to the minimum free radical concentration in the polymerizing system. Radical formation during the dark time is neglected. Assnming that termination is not dependent on the chain length, the rate law for termination can be written as... 

The principle of the pidsed laser technique is simple hut ingenious. A monomer/photoinitiator mixture is irradiated by a pulsed laser beam. Each laser flash generates free radicals which initiate a polymerization process. No new free radicals are formed during the dark time periods. All growing macroradicals formed hy one specific laser pidse have the same chain length within a narrow Poisson distrihution. As the free radical concentration decreases owing to termination processes, the rate of termination decreases according to equation 46, too. 

The minimum polydispersity index from a free-radical polymerization is 1.5 if termination is by combination, or 2.0 if chains ate terminated by disproportionation and/or transfer. Changes in concentrations and temperature during the reaction can lead to much greater polydispersities, however. These concepts of polymerization reaction engineering have been introduced in more detail elsewhere (6). 

However, an important problem arises during the peroxidative removal of phenols from aqueous solutions PX is inactivated by free radicals, as well as by oligomeric and polymeric products formed in the reaction, which attach themselves to the enzyme (Nazari and others 2007). This suicide peroxide inactivation has been shown to reduce the sensitivity and efficiency of PX. Several techniques have been introduced to reduce the extent of suicide inactivation and to improve the lifetime of the active enzyme, such as immobilization. Moreover, Nazari and others (2007) reported a mechanism to prevent and control the suicide peroxide inactivation of horseradish PX by means of the activation and stabilization effects of Ni2+ ion, which was found to be useful in processes such as phenol removal and peroxidative conversion of reducing substrates, in which a high concentration of hydrogen peroxide may lead to irreversible enzyme inactivation. 

SINs. Two SIN compositions were studied, one having 10% oil prepolymer and the other 20% oil prepolymer, both dissolved in the styrene-DVB monomer solution. During the synthesis several morphological changes occurred in the mixture. Early in the reaction all components formed a mutual clear solution which was slightly yellow due to the original color of the prepolymer. As the free radical polymerization of styrene began, the polystyrene first produced remained soluble. At a critical concentration, phase separation... 

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