Polymerization kinetics degree

Our results show that the network density (vg - 1/Q Q = swelling degree) of the crosslinked polymers is a function of the light intensity, the exposure time, the acrylate content, the molecular weight of the uncrosslinked silicone, and also of the length of the spacer group between the acrylate or methacrylate unit and the silicone backbone. Oxygen influences only the polymerization kinetics, but it does not influence the network density. 

The objective of the present work was to determine the influence of the light intensity on the polymerization kinetics and on the temperature profile of acrylate and vinyl ether monomers exposed to UV radiation as thin films, as well as the effect of the sample initial temperature on the polymerization rate and final degree of cure. For this purpose, a new method has been developed, based on real-time infrared (RTIR) spectroscopy 14, which permits to monitor in-situ the temperature of thin films undergoing high-speed photopolymerization, without introducing any additive in the UV-curable formulation 15. This technique proved particularly well suited to addressing the issue of thermal runaway which was recently considered to occur in laser-induced polymerization of divinyl ethers 13>16. 

It can be shown that the degree of polymerization in emulsion polymerization can be derived from general polymerization kinetics [Eq. (3.79)] by neglecting chain transfer ... 

The polymerization kinetics of m-dodecalactam in chemical processing has been investigated in a more limited number of publications in comparison with e-caprolactam. It is not really possible to compare different data therefore only the results of Ref.37 will be discussed below. It was shown that up to a degree of conversionp 0.7, the kinetics of anionic activated polymerization of co-dode-calactam is described by the first-order equation ... 

Engineering of polymerization reactions requires a detailed knowledge of the phenomena that take place in the polymer reactor. This entails a model of the polymerization kinetics and the heat and mass transfer features of the particular polymerization and process. Polymerization reactions are usually complex and a certain degree of mathematical sophistication is required for effective modeling. Excursions into the details of particular reactions or modeling techniques are beyond the scope of this introductory text and this chapter is therefore limited to a review of the special considerations that apply in the case of various polymerizations and processes. Most of the following discussions are necessarily qualitative, for space reasons. 

For values of a between 1 and 10, the character of the polymerization kinetics is intermediate between that of emulsion and that of solution polymerization. This is the region of suspension or pearl polymerization, where the rate and degree of polymerization are somewhat higher than for reaction in solution. The value... 

The aforesaid complexities make it virtually impossible to write explicit general equations for the rate of polymerization, kinetic chain length, average degree of polymerization as has been done above for a completely dissociated ionic initiator. With the exception of those simple cases discussed above, each system in anionic polymerization represents a kinetically unique problem and must be solved separately. 

When, polymerization kinetics was analyzed at high degrees of conversion, however, there was a discrepancy between the calculated and experimental kinetic curves. 

A number of other aspects of polymerization in vesicles studied systematically by this group include initiation chemistry, cross-linking, monomer-surfactant compatibility, polymerization kinetics, and incorporation of polymerizable surfactants. Although phase separation was observed under all conditions, the degree of the phase separation appears to depend heavily on each of these polymerization conditions in a surprisingly intuitive way. 

The kinetic chain length should be related to the number-average degree of polymerization. The degree of complexity of this relation will depend on the existence or otherwise of side (chain-transfer) reactions. We now consider first the case where there are no chain-transfer reactions. By definition... 

ATRP a transition metal complex is needed for the activation of the alkyl-halide-ended macromolecules, and a wider range of temperatures can be applied. In both cases, the polymerization kinetics are governed by the activation-deactivation equilibrium and by the persistent radical effect [6]. The number-average degree of polymerization DP ) is calculated by the ratio of the initial monomer concentration to the initiator (i.e., alkoxyamine or alkyl halide) concentration, multiplied by monomer conversion. 

For instance, the kinetics of a propylene polymerization promoted by SiOa-supported metallocene catalysts depends on various factors the applied reaction engineering (gas-phase, bulk, or slurry-polymerization), the degree of catalyst/ cocatalyst distribution on the support, and the reaction conditions and parameters chosen. 

How is the chain length estimated If we define the instantaneous chain length as the ratio between the rate of propagation and rate of termination, we reach an expression for the kinetic degree of polymerization, DP, (equivalent to the number of mers in the chain) as follows ... 

Because of the high degree of unsaturation present in the polyester resin, the fully cured system was highly crosslinked. Assuming typical polymerization kinetics apply to these systems, elementary kinetics analysis indicates that the reaction order... 

The polymerization rate is directly proportional to the monomer concentration for ideal free radical polymerization kinetics. Deviations from this first-order kinetics can be caused by a whole series of effects which must be checked by separate kinetic experiments. These effects include cage effects during initiator free radical formation, solvation of or complex formation by the initiator free radicals, termination of the kinetic chain by primary free radicals, diffusion controlled termination reactions, and transfer reactions with reduction in the degree of polymerization. Deviations from the square root dependence on initiator concentration are to be primarily expected for termination by primary free radicals and for transfer reactions with reduction in the degree of polymerization. 

Kinetics, degrees of polymerization, and constitution can be changed, however, by a series of other reactions (see Section 20.4). Under certain conditions, for example, the appearance of cauliflower-shaped forms, frequently representing cross-linked polymers, is observed (popcorn polymerization). 

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