End groups and molecular weight

The individual oligomers, arising from disproportionation (90) and chain growth (92—94), viz. 

Accordingly, the molecular weight of cationic polymers calculated from viscosity measurements corresponds to one basic group per macromolecule [184]. The number of polymer molecules (as well as of basic groups) is very close to the initial initiator concentration and remains constant over a long period, except the very beginning of polymerization [176, 177, 180, 188]. 

Whereas structure (113) prevails in cationic caprolactam polymers prepared at low temperature and short reaction periods, the fraction of amidine groups increases with temperature and time of polymerization. However, only small fractions of carboxyl groups were found in cationic polymers [180]. Only fractionated polymers contained equivalent amounts of basic and carboxylic groups which could also arise from hydrolysis of acyllactam groups [213]. 

The molecular weight distribution of cationic polymers is broader than the statistical one because new growth centres are formed during the polymerization. The presence of two maxima in the later steles of polymerization indicates the superimposition of two reaction mechanisms [213]. 

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One of the best studies of the relationship between polymer structure, end groups and molecular-weight distribution, and the mechanism of its formation is still an old classical study by Brown andMatheson on the system styrene-trichloroacetic acid. 

L.A. Narkon, Research of Additives, End Groups and Molecular-Weight Characteristics Effect on Polysulfone Thermoresistance, 1984, G.S. Petrov RIPM, Moscow, Russia. [Thesis on Chemical Sciences], (In Russian)... 

The structure of polyamide fibers is defined by both chemical and physical parameters. The chemical parameters are related mainly to the constitution of the polyamide molecule and are concerned primarily with its monomeric units, end-groups, and molecular weight. The physical parameters are related essentially to chain conformation, orientation of both polymer molecule segments and aggregates, and to crystallinity. 

Polybutadienes with carboxyl end groups and molecular weights of 10000 are produced with increased initiator concentration, addition of dianions, and termination with, for example, CO2. The subsequent conversion with polyisocyanates extends the chains and cross-links the product. Such polymers are conceived as liquid rubbers for the pour molding of tires. 

Vanden Eynde, X., Bertrand, R, Dubois, R, Jerome, R. (1998) Influence of end group and molecular weight on polybutadiene fingerprint secondary ion mass spectra. Macromolecules, 31,6409-6416. 

Nonstoichiometric Reactions. This addition of an SH group to a carbon-carbon double bond involves radical intermediates, but nevertheless exhibits the typical features of a polycondensation reaction. The end group and molecular weight are controlled by stoichiometry of the reactants (473). 

End groups and molecular weight are controlled by the diamine concentration (485). The introduction of protecting groups results in the following reactions (486) ... 

Some general known relationship between flammability and polymer structure are reviewed. Our studies on relating polymer end groups and molecular weights to flammability indicated that the known thermal degradation mechanisms for nylon 6 and polyethylene terephthalate (PET) are, in part, related to their flammability behavior. 

Figure 5.185 shows the process of thermal-oxidative degradation of polycarbonate [38]. Thermal-oxidative degradation proceeds hy radical chain reaction and is influenced by end groups and molecular weight. Figure 5.186 [769]. In addition, free bisphenol A and sodium salts catalyze oxidation.

The values of kact and Katrp can be determined independently, as described above, and the values of kjeact can be calculated from the ratio kact/KATRP, which is one of the commonly used approaches. Alternative experimental methods for determination of kdeact include the clock reaction wherein radicals are simultaneously trapped by TEMPO and the deactivator XMt Lni, " or analysis of the initial degrees of polymerization with no reactivation, end groups, and molecular weight distributions. Additionally, k[Pg.331]

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