Copolymerization-conversion prediction from

Prediction of Copolymerization Conversion from Reactor Head-Space Vapor Composition... 

They were able to observe that inereased styrene eoneentrations reduces the polymerization rates of both methaerylate and styrene due to an inerease in the termination rate and due to flie stability of the styryl radical. Raising styrene concentrations also inereases the final methacrylate conversion, but the final styrene conversion decreases because styrene plasticizes the network, allowing methacrylate conversion to rise at higher styrene concentrations. The final concentration of radicals is reduced at higher styrene concentrations, because of an increase in the bimolecular termination rate for networks with low cross-link densities. The proportion of styryl radicals trapped in the vitrified matrix was found to be markedly higher flian the proportion predicted from the ratio of styrene monomer in the feed resin or from the copolymerization rate constants... 

Tanaka et al. used NPLC and RPLC to determine CCD of PMMA- -PS with different compositions and conversions synthesized from the copolymerization of methyl methacrylate and co-p-vinylbenzyl polystyrene macro monomer [ 158]. The good agreement between CCD obtained by both HPLC modes showed that the molecular weight effect on the CCD is negligible. As the macromonomer content increases, the CCD becomes sharper. These results are in accordance with the theoretical predictions. As the conversion increases at the same feed composition, the CCD becomes broader towards the low macromonomer content side, which is in contrast to the CCD of the samples obtained previously from oo-methacryloyl polystyrene macro monomer [159]. They also showed that the CCD is broadened as the graft length increases, in copolymer samples with a similar composition, in accordance with the theoretical prediction [159]. 

As for step copolymerization, differences in monomer reactivity in chain copolymerization affect the sequence distribution of the different repeat units in the copolymer molecules formed. The most reactive monomer again is incorporated preferentially into the copolymer chains but, because of the different nature of chain polymerization, high molar mass copolymer molecules are formed early in the reaction. Thus, at low overall conversions of the comonomers, the high molar mass copolymer molecules formed can have compositions which differ significantly from the composition of the initial comonomer mixture. Also in contrast to step copolymerization, theoretical prediction of the relative rates at which the different monomers add to a growing chain is more firmly established. In the next section a general theoretical treatment of chain copolymerization of two monomers is presented and introduces an approach which can be applied to derive equations for more complex chain copolymerizations involving three or more monomers. 

In a recent study, Tasdelen et al. synthesized a phenacyl morpholine-4-dithiocarbamate, which can act as both a photoiniferter and reversible addition fragmentation chain transfer (RAFT) agent. Polymerization of styrene was carried out in bulk under UV irradiation at above 300 nm at room temperature. The polymerization showed living characteristics up to 50% conversions and produced well-defined polymers with molecular weights close to those predicted from theory and relatively narrow poyldispersities (Mw/Mn 1.30). End group determination and block copolymerization... 

The first quantitative model, which appeared in 1971, also accounted for possible charge-transfer complex formation (45). Deviation from the terminal model for bulk polymerization was shown to be due to antepenultimate effects (46). Mote recent work with numerical computation and C-nmr spectroscopy data on SAN sequence distributions indicates that the penultimate model is the most appropriate for bulk SAN copolymerization (47,48). A kinetic model for azeotropic SAN copolymerization in toluene has been developed that successfully predicts conversion, rate, and average molecular weight for conversions up to 50% (49). 

Using copolymerization theory and well known phase equilibrium laws a mathematical model is reported for predicting conversions in an emulsion polymerization reactor. The model is demonstrated to accurately predict conversions from the head space vapor compositions during copolymerization reactions for two commercial products. However, it appears that for products with compositions lower than the azeotropic compositions the model becomes semi-empirical. 

Data of Nomura and Funita (12). The predictive capabilities of EPM for copolymerizations are shown in Figures 8-9. Nomura has published a very extensive set of seeded experimental data for the system styrene-MMA. Figures 8 and 9 summarize the EPM calculations for two of these runs which were carried out in a batch reactor at 50 °C at an initiator concentration of 1.25 g dm 3 water. The concentration of the seeded particles was 6x10 dm 3 and the total mass of monomer was 200 g dm 3. The ratio of the mass of MMA to the total monomer was 0.5 and 0.1 in Figures 8 and 9 respectively. The agreement between the measured and predicted values of the total monomer conversion, the copolymer composition, and the concentration of the two monomers in the latex particles is excellent. The transition from Interval II to Interval III is predicted satisfactorily. In accordance with the experimental observations, EPM predicted no new particle formation under the conditions of this run. 

The results of several copolymerization experiments with 7 are given in Table 3.8, from which it is clear that the assumption of similarity between 7 and benzyl methacrylate is reasonable. From Fig. 3.4. it is predicted that both MMA and MAN should copolymerize with 7 almost ideally , whereas styrene will deviate considerably from ideality . These predictions are verified by the results in Table 3.8. If the azo monomer is incorporated into the polymer in the same proportion as it is present in the initial monomer mixture, then it is possible to convert the, relatively valuable, azo monomer essentially 100% into polymer without changing the composition of the copolymer with conversion an important consideration for the technical utilisation of such products as the starting materials for graft copolymers. If the poly-... 

Simultaneous polymerization of two monomers by chain initiation usually results in a copolymer whose composition is different from that of the feed. This shows that different monomers have different tendencies to undergo copolymerization. These tendencies often have little or no resemblance to their behavior in homopolymerization. For example, vinyl acetate polymerizes about twenty times as fast as styrene in a free-radical reaction, but the product obtained by free-radical polymerization of a mixture of vinyl acetate and styrene is found to be almost pure polystyrene with hardly any content of vinyl acetate. By contrast, maleic anhydride, which has very little or no tendency to undergo homopolymerization with radical initiation, readily copolymerizes with styrene forming one-to-one copolymers. The composition of a copolymeir thus cannot be predicted simply from a knowledge of the polymerization rates of the different monomers individually. The simple copolymer model described below accounts for the copolymerization behavior of monomer pairs. It enables one to calculate the distribution of sequences of each monomer in the macromolecule and the drift of copolymer composition with the extent of conversion of monomers to polymer. 

To represent dispersion polymerization in conventional liquid media, several models have been reported in the literature, mainly focused on the particle formation and growth [33, 34] or on the reaction kinetics. Since our first aim is the reliable description of the reaction kinetics, we focus on the second type of models only. The model developed by Ahmed and Poehlein [35, 36], applied to the dispersion polymerization of styrene in ethanol, was probably the first one from which the polymerization rates in the two reaction loci have been calculated. A more comprehensive model was later reported by Saenz and Asua [37] for the dispersion copolymerization of styrene and butyl acrylate in ethanol-water medium. The particle growth as well as the entire MWD were predicted, once more evaluating the reaction rates in both phases and accounting for an irreversible radical mass transport from the continuous to the dispersed phase. Finally, a further model predicting conversion, particle number, and particle size distribution was proposed by Araujo and Pinto [38] for the dispersion polymerization of styrene in ethanol. 

With Q-e values (20), the reactivity ratios of comonomers, rj and r, can be estimated using Equations 2 and 3. Monomer reactivity ratios can also be determined empirically by carrying out a series of copolymerizations and determining the polymer composition at low conversions. (20b) The reactivity ratios can be used to predict the nature of the copolymer type from a polymerization. For example, when the product of q and r has a value of zero, an alternating copolymer is likely to result from the copolymerization. On the other hand, when the product is near the value of one, the copolymer is likely to be a random copolymer. In a copolymerization process, if one of the comonomers does not homopolymerize, such as in the copolymerization of styrene (rj=0.019) and maleic anhydride (rj=0.0) at 50 °C (20,21), the polymer produced would be an alternating copolymer (Reaction 4). 

Figure 7.4 shows the comparison of instantaneous and overall conversion and free monomer during the seeded semibatch emulsion copolymerizations of n-butyl acrylate/ methyl methacrylate (BA/MMA) calculated online from calorimetric measuranents and off-line by gravimetry [29]. These results show that calorimetry predicts overall conversion well but that the prediction of instantaneous conversion and free monomer is less accurate, especially when the polymerization is carried out under starved conditions and/or the monomer concentrations are very low in the reactor, as for the MMA in Figure 7.4d. Under these polymerization conditions, other more accurate techniques (but less robust and more expensive) such as Raman spectroscopy might be better suited for monitoring free monomer concentration [29].

Batch trials were performed on a kneader reactor where a bulk co-polymerization was carried out. Polymerization conversion, viscosity build, reaction kinetics, and heat transfer calculations were performed using the experimental data from the batch trials. A continuous process was proposed for this bulk copolymerization and the models and results from the batch trials were used in designing the continuous process. Predictions of the continuous process using the batch trial data are compared to the actual continuous process, with a focus on polymer conversion, heat transfer, and torque prediction. 

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