Instantaneous initiation

Figure 3.3 Cumulative ( ) and instantaneous ( ) initiator efficiency (/) of AIBN as initiator in S polymerization (50% v/v toluene, 70 °C) as a function of monomer conversion (lines are a polynomial fit to the datapoints).1,32...

Sulfonation of the common feedstocks proceeds with a highly exothermic instantaneous initial reaction, followed by a fast but not instant step that is also highly exothermic. The second reaction does not always proceed to completion (e.g., LAB, FAME) in the lower zone of a short residence time falling film reactor (FFR). For these organic feedstocks aging under well-defined conditions of temperature and reaction time is required. 

Instantaneous monomer feed flow-rate. Instantaneous initiator feed flow-rate. Time-averaged monomer solution flow-rate in oscillatory steady-state. 

Fig. 17 — Chemical Instantaneous Initiator open end of the fuse lighter.

How is the instantaneous initial velocity of an enzymatic reaction measured What precautions must be taken to ensure that a true instantaneous velocity is being obtained ... 

In living polymerization, with instantaneous initiation reaction and no chainterminating process, the MWD of the living polymer can be expressed by a Poisson... 

Assuming that we are dealing with so-called "living" polymerization (in the absence of chain termination in the course of polymerization), the kinetic mechanism of (o-dodecalactam polymerization with instantaneous initiation can be written as... 

The rate of radical generation or production (Rpr) is related to the rate constant for initiator decomposition, c, by Equation 10.3 where [I] is the instantaneous initiator concentration. The factor of 2 is included because two initiator or primary radicals are... 

The monomeric radical anion is dimerized [reaction (41)1, and polymerization takes place on the ions or ion pairs. The equilibrium (46) is very rapidly established. Radical defects decay by combination thus naphthalenesodium is used quantitatively for practically instantaneous initiation. This method can therefore also be used to prepare polymer chains of uniform length. The regenerated naphthalene does not usually cause trouble. In some cases, the aromatic residue can be incorporated into the chains [190] (the metal cation is omitted for simplicity). 

It continuously increases if initiation is slow, until it reaches the same value as that for the ideal case of instantaneous initiation. If initiation is fast but termination occurs, the tangent decreases continuously following the declining concentration of growing species as shown in Fig. 2, which often leads to only partial monomer conversion. For example, if [M]0 =... 

Thus, termination will have a mostly kinetic effect. Figure 4 shows the semilogarithmic plots for various ratios R, = k,/kp, taking kp 1 mol-1L-sec, arbitrary concentrations [M]0 = 1 mol/L, [I]0 = 0.001 mol/L, and assuming instantaneous initiation. 

Rate expressions that depend on more than one concentration are more difficult to obtain experimentally than those that depend just on one. One method is to find the instantaneous initial rates of reaction for several values of one of the concentrations, holding the other initial concentrations fixed from one run to the next. The experiment can then be repeated, changing one of the other concentrations. The following example illustrates this procedure. 

A large tank is connected to a smaller tank by means of a valve. The large tank contains N2 at 690 kPa while the small tank is evacuated. If the valve leaks between the two tanks and the rate of leakage of gas is proportional to the pressure difference between the two tanks p - P2), how long does it take for the pressure in the small tank to be one-half its final value The instantaneous initial flow rate with the small tank evacuated is 0.091 kg mol/hr. 

It is doubtful, however, that a true living system without termination or transfer exists in these polymerizations instead we believe that the narrow distributions may result from a combination of essentially instantaneous initiation, relatively long kinetic lifetime, and kinetic termination without transfer. H. Morawetz has derived an equation relating the molecular weight distribution to the relative rates of propagation and termination and the concentration of active species for such a case ( ). The equation accounts for the possible occurrence of narrow distributions, and we are presently experimentally investigating these calculations and predictions for the polymerization of the p-isopropyl monomer. 

The first successful experimental observation of the dynamics of the chemical bond was accomplished in the 1980s [2]. The clocking of such an ultrafast event requires an almost instantaneous initiation of the dynamics which can be accomplished by a femtosecond laser pulse. After this flash of electromagnetic radiation -the pump pulse - the dynamics of the induced photochemical reaction is probed via another ultrashort interaction with a probe pulse. This is repeated at various time delays between the pump and probe pulse and a series of snapshots are obtained which together constitute a molecular movie of the dynamics. 

Living polymers resulting from an instantaneously initiated but non-terminated polymerization, have a nearly Poisson molecular weight distribution, provided that Mo > Me. The polymerization seems to cease as the concentration of the residual monomer attains its equilibrium value - no further conversion of the monomer into polymer could be detected at that stage of the reaction. Nevertheless, the system is not yet in its ultimate equilibrium state. 

The scenarios in series A concern initiation by purposely added initiator RX. Figures 1-8 (A-D) and 10 (A-D) show the diagnostic plots for the ideal case (instantaneous initiation, scenario Al, dotted lines) together with the effect of the various complicating factors, i.e., instantaneous initiation plus zero order chain transfer to monomer (scenario A2a), instantaneous initiation plus first order chain transfer to monomer (scenario A2b), instantaneous initiation plus both... 

Fig, IA. Number of polymer chains vs conversion. B Number average molecular weight vs conversion. C Rate of polymerization vs time. D Conversion vs time. Diagnostic plots for instantaneous initiation (At), with various chain transfers (A2a, A2b, A2c) and for slow initiations (A3a, A3b)... 

In series C both purposeful-initiation and H20 induced-initiation exist. Figure 5A-D shows the diagnostic plots for instantaneous initiation by H20 ... 

The instantaneous initial drive that causes fluid pressure to begin to equilibrate can be expressed by... 

We derived estimates of relative mixing times by considering the volume of fluid that is needed to move in each scenario in order to reach equilibration and the relative mixing drive (an instantaneous initial volumetric rate) as estimated from the permeability, viscosity and pressure difference or diffusion coefficient depending upon the mixing mechanism. 

Instantaneous initiation efBciency of AIBN during solution styrene polymerization... 

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