Living polymers association

Propagation of Living Polymers Associated with Bivalent Cations... 

Similar divergences are found for lithium poly-2,4-hexadiene solution (1 10-3 M in living polymers) for which a sixfold decrease of viscosity upon protonation corresponding to a degree of association of 1.7 was reported 113), whereas only a threefold decrease, i.e. a degree of association of 1.4 was indicated earlier 1,8). The difference between the 1.7 and 1.4 values was tentatively attributed to a slow decomposition of the active ends over a period of two weeks U8) notwithstanding their reported good... 

Anionic polymerisation of hydrocarbon monomers is initiated by lithium butyl to produce a living polymer the association number of which in solution is required to elucidate the kinetics. When the living polymer (for example polystyryl lithium) is terminated, the polystyrene can be isolated and a solution then made to determine its molecular weight, M. If the living polymer is associated in solution, the ratio of its... 

LIVING POLYMERS, AND ELECTRON TRANSFER PROCESSES, Interscience Publishers, 1968, persumably pp. 499 and 500) has himself recently used this Technique albeit without acknowledging the original or later association work, the development of the capping technique which he has exploited, nor his faulty commentary."... 

When the oxygen deactivates the freeze dried living polymers without additives, the coupling reaction becomes predominant and can reach up to 60%. We explain this result by the association of the living ends preexisting In the solution, and kept In the solid state. The proximity of these carbanlons and consequently of the radical after the electronic transfer favours the coupling reactions. 

From the Table IV, it also shows that the low styrene content in the copolymer may relate to the polymerization temperature. As the polymerization temperature was increased from 5° to 70°C, the styrene content of the butadiene-styrene copolymer decreased from 21.7% to 9.1%, respectively. The decreasing in styrene content at higher temperature is consistent with the paper reported by Adams and his associates (16) for thermal stability of "living" polymer-lithium system. In Adams paper, it was concluded that the formation of lithium hydride from polystyryllithium and polybutadienyllithium did occur at high temperature in hydrocarbon solvent. The thermal stability of polystyryllithium in cyclohexane is poorer than polybutadienyllithium. From these results, it appears that the decreasing in styrene content in lithium morpholinide initiated copolymerization at higher temperature is believed to be associated with the formation of lithium hydride. 

Interestingly, there have been repeated attempts to view such gradual structural changes due to chemical equilibria as phase transitions as well [262]. Instructive examples for such an analysis are living polymers — for example, in demixing solutions of polymers [263] and in sulfur [264], where the reversible polymerization process has been treated as a second-order phase transition. The experimental evidence for such an interpretation is, however, at best weak [265], and classical association models [266] describe the thermodynamic properties equally well. 

All authors accept the alternating incorporation of epoxide and anhydride into the macromolecular chain 36 39.40.45 52.73-74). However, the mechanisms of termination and chain transfer have not yet been elucidated. Although the lability of the nitrogen atom is obvious 39 40 44> and its salts or associates are readily thermally decomposed 89), Fischer 39 detected its presence in precipitated polyesters by elemental analysis. A simple calculation confirms the presence of the nitrogen atom in almost every tenth macromolecule. In this case, the isolated polyester might be a living polymer and, on the addition of monomers, it might initiate another copolymerization. Similar experiments have not been reported so far. 

The kinetic scheme with constant reaction of the polymer/monomer droplet increases fairly quickly with conversion, and the mobility of the polymer chains rapidly falls below the mobility of the monomer. The reduced diffusion of live polymer chains in the droplet will reduce the rate of termination of polymerization. The associated increase in the number of radicals will cause a rapid increase in the polymerization rate. This phenomenon is well known as the Trommsdorf or gel effect [8,9]. The gel effect causes a growth of the polymer chain length and widening of the molecular weight distribution (Figure 9.5). 

Further work by Schulz and his co-worker has shown the results for the polymethylmethacryl sodium system to be influenced by the bifunctional nature of the living polymer employed, with in particular a contribution from an intramolecular association of ion pairs. This has led to a careful re-evaluation of the system using one-ended living polymer in the presence of excess of common ion salt, Na+BPh4 , with, for example, a resulting estimate for / p( ) at —73 °C of 168 s" somewhat higher than previously reported. 

Here we can draw an analogy with the equilibrium dissociation reaction, when the association rate constant in equilibrium is not limited by diffusion, regardless of the viscosity of the medium. In our opinion, this question requires at present a theoretical and experimental investigation. It is customary to assume that radical polymerization is characterized by a rather intensive chain termination reaction and a short time for the propagation of one chain, as compared to the time of polymerization. The existence of continuous processes ( living polymers) has been ascertained for anionic9 and cationic polymerization10, where there is no bimolecular interaction of active centers with one another. Let us now examine certain radical polymerization processes in which the chain termination reactions are considerably inhibited or almost excluded. 

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