Low propagation

The exceptionally low propagation constants of t-butyl and of phenyl methacrylate are notable. The polymerization of the former monomer was thoroughly examinedS5). At temperatures even as high as 25 °C this reaction, when performed in THF in the presence of salts depressing dissociation of ion-pairs, yields polymers of highly uniform size. The reaction is strictly first order in growing polymers and in monomer, and no... 

A careful consideration of Eq. 3-140b shows that for a strong retarder (z 1), the polymerization rate will be negligible until the inhibitor concentration is markedly reduced. When the inhibitor concentration becomes sufficiently low, propagation can become competitive with the inhibition reaction. This is more readily seen by considering the equation... 

The rate constants of a-hydrogen atom abstraction from four hydrocarbons by cumylperoxy, tetralylperoxy, and 9,10-dihdroanthracyl-9-peroxy radicals and by the normal chain-carrying peroxy radicals are compared in Table VIII. The results show that the reactivities of peroxy radicals are affected by the nature of the organic group. The relatively low propagation constant for the oxidation of pure cumene may be caused by the low reactivity of the cumylperoxy radical. 

Advantages Accurate, very low propagation delay Disadvantages Can be realized with fewer parts... 

Fry Nicholls (Ref 6) studied the expln of MAPP/air vapor clouds. MAPP is a mixt of 51/26/23%methylacetylene/propane/propadiene. Results of their expts in terms of Mach numbers for the propagation velocity are shown in Figs 13, 14 and 15. In Figs 13 and 14 initiation sources are indicated. Obviously, weak initiation results in low propagation velocity. The abcissa in Figs 13 and 14 is the distance (inches) from the initiation source. Fig 15 shows the mean values of the measured Mach numbers for detonations of various fuel/air compns. It also establishes the detonability range of these mixts of about 2.4 to 10 volume % of fuel. Inci-... 

The solder-filled cable was by far the most stable configuration, having the highest recovery current (/mr), high minimum propagating current (/mp), and very low propagation velocity for currents up to Ic (approximately 2000 A at 4 T). 

The incorporation of more than two isoprene units in the coupling product is limited due to the very low propagating rate of this monomer at room temperature. Moreover, the massive coupling of the P — PI° radical is possible because of its low tendency to be deactivated by Co(acac)2 [60]. 

Big LEO global communication systems, also called LEO constellations, such as Globalstar and Iridium , provide a mobile communication system using a net formed by a huge number of satellites (up to 90 positioned in few orbit plans). These communication systems use this type of orbit mainly due to the low propagation delay (20-30 m) of the signal. 

Bulk Polymerization. The idea of bulk polymerization is attractive, since the polymer would not require water removal and the process would not have the low propagation rates and high chain transfer rates of solution processes (see Bulk and Solution Polymerizations Reactors). But bulk polymerization of acrylonitrile is complex. Even after many investigations into the kinetics of the polymerization, it is still not completely imderstood. The complexity arises because the polymer precipitates from the reaction mixture barely swollen by its monomer. The heterogeneity leads to kinetics that deviate from normal. 

Equation 160 shows that the polymerization rate is inversely proportional to the inhibitor concentration. It should be kept in mind that the inhibitor concentration will decrease during the reaction. Each free radical generated by the initiation process will consume one inhibitor molecule. If the inhibitor concentration finally becomes sufficiently low, propagation can become competitive with the inhibition reaction. 

In free radical polymerization, initiators are used that decompose (form radicals) with a moderate rate, so that new radicals are formed during the entire process. Since termination is also moderately rapid, the concentration of radicals is always low. Propagation is very rapid, and though the growing chains "live" only a short... 

The radiation-induced cationic polymerization in the presence of onium salts has attained practical importance for the EB curing of systems containing epoxides or vinyl ethers [22,23]. The chemical structures of typical compounds were presented in Table 3.23. THE does not play a role in this context, because of its very low propagation rate constant (kp 4 x 10 lmol s ). A reaction mechanism for the polymerization of vinyl ethers in the presence of an iodonium salt, as proposed by Crivello [22], is shown in Scheme 5.8. 

The successful fabrication of planar waveguides with proper spectroscopic properties and low propagation loss is not the ultimate goal. Demonstration of efficient laser or optical amplification requires a channel waveguide configuration, with lateral and transverse confinement. This supplementary step often generates extra propagation loss. 

Georges and co-workers [41] reported the first controlled polymerisation using the NMP technique. The stable free radical 2,2,6,6-tetramethyl-l-piperidynyl-N-oxy (TEMPO) was initially used, with a thermal radical initiator, for the polymerisation of styrene. NMP polymerisations usnally require higher polymerisation temperatures, and it was not possible to polymerise acrylates in the presence of excess TEMPO in the early systems, due to the very low propagation rate. The radical polymerisation... 

Finally, a further important barrier that may become important, especially at the end of the breeding cycle, is the limited propagation rate. Low propagation rates limit introduction on the market. 

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