Polymerization kinetics mass fractions

In spite of the presence of Nd-clusters, partial alkylation and micro heterogeneities the number of active Nd-species seems to be fairly constant during the course of a polymerization. Otherwise neither consistent polymerization kinetics (particularly lst-order monomer consumption up to high monomer conversion) nor linear increases of molar mass during the whole course of the polymerization would be observed in so many studies. It therefore can be concluded that the fraction of active Nd as well as the number of active catalyst species are fixed either at an early stage of the polymerization or even prior to initiation of the polymerization. It can be speculated whether the fixation of the number of active species occurs during catalyst prefor-mation/activation or even during the preparation of the Nd compound. In contrast to this consideration Jun et al. report on the decay of active cen-... 

Still some controversy about the precise mechanism, over the years a consensus has emerged that the F-T reaction is a polymerization of surface CH2 species derived from the hydrogenation of adsorbed CO. This is for example shown by the product hydrocarbon distribution where there is a monotonic decrease in yield with increase in molecular size. Plotting og WjN) against W (W = mass fraction N = carbon number) gives a characteristic graph (dotted line, Figure 15) which is typical for polymerization kinetics. 

The polymerization is mainly processed with acrylic acid, as mentioned before. This monomer has very fast reaction kinetics and is successfully tested in spray polymerization processes. In addition the salts of the acrylic acid, acrylates, are investigated. Four different acrylates have been generated by neutralization of the acid. These are lithium, sodium, potassium and ammonium acrylate by adding their hydroxides. Because of the limited solubility in water the maximum weight fraction of lithium, sodium, potassium and ammonium is 27.0, 32.2, 59.6 and 42.2%. Acrylic acid has been made available by BASF SE and was received by Sigma Aldrich. To increase the storage stability an inhibitor, hydroquinone monomethylether (MEHQ), with a mass fraction of 180-220 ppm had been added before shipping. 

As important as kinetic mechanism are the phase changes that occur in polymerization. Only a small fraction of polymerizations are carried out only in one phase thus thermodynamics, heat and mass transfer, and the kinetics of the phase change itself all play a role in determining the properties of the product polymer. Table IV indicates the principal types of kinetic mechanisms and reaction media which arise in polymerization reactors. Each of these classes of systems has its own peculiar problems so that polymerization reactor design can often be much more challenging than the design of reactors for short chain molecules. 

By combining thermodynamically-based monomer partitioning relationships for saturation [170] and partial swelling [172] with mass balance equations, Noel et al. [174] proposed a model for saturation and a model for partial swelling that could predict the mole fraction of a specific monomer i in the polymer particles. They showed that the batch emulsion copolymerization behavior predicted by the models presented in this article agreed adequately with experimental results for MA-VAc and MA-Inden (Ind) systems. Karlsson et al. [176] studied the monomer swelling kinetics at 80 °C in Interval III of the seeded emulsion polymerization of isoprene with carboxylated PSt latex particles as the seeds. The authors measured the variation of the isoprene sorption rate into the seed polymer particles with the volume fraction of polymer in the latex particles, and discussed the sorption process of isoprene into the seed polymer particles in Interval III in detail from a thermodynamic point of view. 

Kinetics. Hydrogen mordenite appears to be a good catalyst for the polymerization of n-butylvinylether. At 30 C Qj, the fraction of mass increase at time t, obeys the relationriiip... 

Kinetic investigations presented in [247, 248] showed that use of TiCU as catalyst for industrial piperylene fraction polymerization (components content, mass % rrans-piperylene 60,8, cis-piperylene 37,2, etc.) allows to produce oligopiperylene with high yield (80-95%) with desired MM (80-2000) at comparable high process duration (nearly 1 hour). Polymerization process in toluene medium is characterized by the first orders by catalyst and monomer with constants of chain propagation, transfer on monomer and catalyst rates 1,5, 0,04 and 0,86 l/mole-min accordingly. Oligomers MMD has unimodal character, but with synthesis temperature rise products polydispersity increases. 

In synthesizing polymers in vivo and in vitro, molecular homogenous ( monodisperse ) polymers (i.e., those in which every macromolecule has the same molar mass or molecular weight ) occur only under quite specific conditions. The overwhelming majority of polymer syntheses proceed more or less randomly, and the resulting macromolecular substances have more or less broad molar mass distributions. The kind of molar mass distribution obtained depends on the nature of the polymerization, which may be either thermodynamically or kinetically controlled. Each kind of distribution is characterized by a definite relationship between the mole fraction x and the degree of polymerization X. Consequently, it is possible in many cases to deduce the kind of polymerization involved from the type of distribution function obtained. 

Dijt et al. [41 ] also studied the desorption kinetics with reflectometry for PEO molecules adsorbed on a silica surface by replacing the polymer solution with solvent. For molar masses above 10 g mol no detectable decrease in the adsorbed amount takes place on the time scale of the experiment (hours to days). For lower molar mass some desorption is observed the decrease approaches about 15% for A/ = 7100 g mol. Owing to the high-affinity character of PEO on silica, complete detachment of the polymeric molecules is highly suppressed. With reflectometry one detects the change in the total mass present in flic surface layer. In order to check if changes in the volume fraction profile take place after replacing the polymer solution by solvent, measurements of the layer thickness are more relevant. 

Molecular masses at the onset of phase separation are determinative factors in the appearance of the thermodynamic incompatibihty of the network fragments. At the same time, up to now there are no experimental data on the MM of both components at various stages of reaction and at the onset of phase separation. For the blends of linear PU and PMMA synthesized in situ, we have determined the MM of both components after completion of the reaction. These values were also estimated for pure components obtained under the same conditions. It was found that the kinetic conditions of the reaction determine the MM and MM distribution by simultaneous curing, which are different from the results of polymerization of pure components. These data testify to the marked effect of the reaction conditions on the MM, and in such a way contribute to the understanding of the effect of reaction conditions on the phase segregation and fraction of an interfadal region. 

An example of the molar mass distributions that can be produced by RAFT polymerization is shown in Figure 6.2. The molar mass distributions are narrow (i)mole fraction of dead chains observed is small and consistent with that predicted by kinetic simulation using the usual kinetic parameters. 

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