Monomer conversion dependence

Figure 14A shows experimental N data (see Eq. (22)) plotted against monomer conversion. The additivity of N is valid only for its monomer conversion dependent functions ... 

Equations 1.42 and 1.43 provide the solution for the inverse problem [21]. The forced variation of the reactor geometry and the measurement of monomer conversion dependence on R, enable the estimation of the value. It is important, that... 

As has been indicated above, the termination rate coefficient is—depending on the monomer in question—strongly dependent on the overall monomer conversion. The conversion dependencies of the (average) termination rate coefficient have been reported for several monomers, with most measurements being done via the SP-PLP technique, which allows to point-wise probe the kinetics of the polymerization reaction up to high overall monomer conversions. A typical kt vs monomer conversion dependence is given in Figure 6 for the example of methyl acrylate and dodecyl acrylate. The data are taken from Reference 331. 

Figure 4. Relative monomer conversion depending on incubated temperature.

Figure 5. Monomer conversion depending on reaction time for polymerization using different immobilized CALB in scCOz at 70 "C and 10 MPa. Accurel, QDE2-3-4, and Novozyme-435.

The calculation of the monomer conversion depends on the operation mode. Table 6.3 summarizes the expressions for the different reactors. The instantaneous copolymer composition refers to the composition of the copolymer that is being formed at a given time. Referred to monomer 1 this composition is given by Eq. (60), where is the polymerization rate of monomer i. 

Fig. 3.21 Monomer conversion dependence of number average molar mass (M ) and polydispersity index (M /M ) of macromonomer =-S-S-(PS-Br)2 during the ATRP process...

Combined Chain-Length and Monomer Conversion Dependence... 

Figure C2.1.3. Schematic dependence of tire molecular weight of a polymer as a function of tire degree of monomer conversion for different polymerization reactions.

Unless working with superdried systems or in the presence of proton traps, adventitious water is always present as a proton source. Polymeriza tion rates, monomer conversions, and to some extent polymer molecular weights are dependent on the amount of protic impurities therefore, weU-estabHshed drying methods should be followed to obtain reproducible results. The importance is not the elimination of the last trace of adventitious water, a heroic task, but to estabhsh a more or less constant level of dryness. 

The production rate is 2—4 t/h, depending on the feed rate, monomer concentration in the feed, and conversion. The conversion of isobutylene and isoprene typically ranges from 75—95% and 45—85%, respectively, depending on the grade of butyl mbber being produced. The composition and mol wt of the polymer formed depend on the concentration of the monomers in the reactor Hquid phase and the amount of chain transfer and terminating species present. The Hquid-phase composition is a function of the feed composition and the extent of monomer conversion. In practice, the principal operating variable is the flow rate of the initiator/coinitiator solution to the reactor residence time is normally 30—60 minutes. 

Styrene-based polymer supports are produced by o/w suspension polymerization of styrene and divinylbenzene. Suspension polymerization is usually carried out by using a monomer-soluble initiator such as benzoperoxide (BPO) or 2,2-azo-bis-isobutylnitrile (AIBN) at a temperature of 55-85°C (19). A relatively high initiator concentration of 1-5% (w/w) based on the monomer is used. The time required for complete monomer conversion must be determined by preliminary experiments and is usually between 5 and 20 h, depending on the initiator concentration, the temperature, and the exact composition of the monomer mixture (11-18). 

Lu et al. [86] also studied the effect of initiator concentration on the dispersion polymerization of styrene in ethanol medium by using ACPA as the initiator. They observed that there was a period at the extended monomer conversion in which the polymerization rate was independent of the initiator concentration, although it was dependent on the initiator concentration at the initial stage of polymerization. We also had a similar observation, which was obtained by changing the AIBN concentration in the dispersion polymerization of styrene conducted in isopropanol-water medium. Lu et al. [86] proposed that the polymerization rate beyond 50% conversion could be explained by the usual heterogenous polymer kinetics described by the following equation ... 

There are some reports that values of kp are conversion dependent and that the value decreases at high conversion due to kp becoming limited by the rate of diffusion of monomer. While conversion dependence of kp at extremely high conversions is known, some data that indicate this may need to be reinterpreted, as the conversion dependence of the initiator efficiency was not recognized (Sections 3.3.1.1.3,3.3.2.1.3 and 5.2.1.4). 

For very active transfer agents, the transfer agent-derived radical (T ) may partition between adding to monomer and reacting with the polymeric transfer agent (Pn 1) even at low conversions. The transfer constant measured according to the Mayo or related methods will appear to be dependent on the transfer agent concentration (and on the monomer conversion).40 2 A reverse transfer constant can be defined as follows (eq. 20) ... 

The solvent in a bulk copolymerization comprises the monomers. The nature of the solvent will necessarily change with conversion from monomers to a mixture of monomers and polymers, and, in most cases, the ratio of monomers in the feed will also vary with conversion. For S-AN copolymerization, since the reactivity ratios are different in toluene and in acetonitrile, we should anticipate that the reactivity ratios are different in bulk copolymerizations when the monomer mix is either mostly AN or mostly S. This calls into question the usual method of measuring reactivity ratios by examining the copolymer composition for various monomer feed compositions at very low monomer conversion. We can note that reactivity ratios can be estimated for a single monomer feed composition by analyzing the monomer sequence distribution. Analysis of the dependence of reactivity ratios determined in this manner of monomer feed ratio should therefore provide evidence for solvent effects. These considerations should not be ignored in solution polymerization either. 

The reaction rate in a continuous reactor is dependent on monomer conversion but it does not vary with time once steady-state... 

Initial comparison of CFSTR runs with similar feed conditions indicates conditions for which the monomer conversion may be dependent on mixing speed. However, when the effects of experimental error in monomer conversion and differences in reaction temperature are considered, the monomer conversion is seen to be relatively independent of mixing speed for rpm equal to or greater than 500. Comparing Run 14 with Run 12 reveals a small decrease in monomer conversion in spite of a rise in reactor temperature of 2°C. This indicated the presence of a small amount of bypassing or dead volume at the lower mixing speed. This imperfect mixing pattern would also be present in Run 15. 

Observed monomer concentrations are presented by Figure 2 as a function of cure time and temperature (see Equation 20). At high monomer conversions, the data appear to approach an asymptote. As the extent of network development within the resin advances, the rate of reaction diminishes. Molecular diffusion of macromolecules, initially, and of monomeric molecules, ultimately, becomes severely restricted, resulting in diffusion-controlled reactions (20). The material ultimately becomes a glass. Monomer concentration dynamics are no longer exponential decays. The rate constants become time dependent. For the cure at 60°C, monomer concentration can be described by an exponential function. 

The molecular weight distribution of a polymer produced with a chain shuttling catalyst/CSA system is highly dependent on reaction conditions. The extent of reversibility with the catalyst/CSA pairs was therefore further explored through a series of polymerizations over a range of monomer conversions (i.e., yield). A representative example from this secondary screening process is described below for precatalyst 17. Several members from this well-studied bis(phenoxyimine)-based catalyst family [39] were identified as poor incorporators in the primary screen. A series of ethylene/octene copolymerizations using 17 was performed across a... 

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