Anionic polymerization kinetic chain length

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. 

The block copolymer produced by Bamford s metal carbonyl/halide-terminated polymers photoinitiating systems are, therefore, more versatile than those based on anionic polymerization, since a wide range of monomers may be incorporated into the block. Although the mean block length is controllable through the parameters that normally determine the mean kinetic chain length in a free radical polymerization, the molecular weight distributions are, of course, much broader than with ionic polymerization and the polymers are, therefore, less well defined,... 

In the section on anionic polymerization, we mentioned that it was time for you to do some work So here is the homework question you have been dreading. Show that in an anionic polymerization of an appropriate monomer in a protic solvent, NH3, initiated using NaNHj, the rate of polymerization is second-order in monomer concentration. Also, obtain an expression for the kinetic chain length. Try not to throw up oh your answer sheet ... 

In considering batch polymerization systems, the kinetics of polymerization can be used directly. For anionic polymerization with chain transfer, the kinetic chain length (x) can be shown to be a function of the monomer concentration ... 

The first example of a living polyolefin with a uniform chain length was disclosed in 1979 by Doi, Ueki and Keii 47,48) who used the soluble Ziegler-Natta catalyst composed of V(acac)3 (acac = acetylacetonate anion) and A1(C2H5)2C1 for the polymerization of propylene. In this review, we deal with the kinetics and mechanism of living coordination polymerization of a-olefins with soluble Ziegler-Natta catalysts and the synthesis of well-defined block copolymers by the use of living polyolefins. 

Apart from nitrate ions, the direct reduction of carbonate, phosphate, and silicate anions have all been reported. Some controversy surrounds the electroreduction of sulfate ions water may be implicated in this process. Inman and Wrench could only induce cathodic electroactivity of sulfate ions dissolved in a chloride melt by release of SO3, the conjugate acid, with a stronger Lux-Flood acid, metaphosphate, P03. While the alkali metal and alkaline earth sulfates, carbonates, and nitrates are clearly ionic, borate, phosphate, and silicate melts are highly polymerized. In such systems, the mobile cations move freely about the anion lattice network, which comprises a temperature- and compositional-dependent equilibrium between ion fragments of variable chain length. Inman and Franks observed kinetically limited electroreduction processes in a phosphate melt, as might be expected if only the smallest fragments of the dynamic polymer equilibrium are electroactive. 

Most Probable (Flory) Distribution The most probable or Rory distribution is described by the following equations. For polymerization problems. Equation 16.53 is appropriate, since chains of length zero are not considered Equation 16.52 is included for completeness only. It is a single-parameter distribution, with the shape of the distribution dependent only on the value of a. The Rory distribution describes the NCLD for a number of kinetic schemes, including batch condensation polymerization and anionic polymerization in a CSTR ... 

From the kinetics of the oxirane polymerization initiated hy alcoholate (l6) and hy fluorenyl potassium (27) and as fluorenyl and dihydronaphthalene mono anion (28) have approximately the same basicity, the ka2 over kpr0p ratio may be estimated to 20. Therefore, the length of the two growing polyether chains must be largely independent on the nature of the initiating site. 

A special type of kinetic enhancement in linear polymer is observed when the polymerization is carried out via the activated monomer (AM) mechanism. Instead of active species located on the chain ends, the active spedes is located on some of the monomer molecules. Most often, such an activation proceeds via proton transfer reactions - protonated (cationic process) or deprotonated (anionic process) monomer can further react with the chain ends of linear polymer, inaeas-ing their lengths. 

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