Kinetics of anionic polymerization:I. The effect of the concentration of starting materials on the chain reaction growth rate
By the principle of stationarity:
Coordination polymerization. Explain monometallic and bimetallic mechanisms of stereoregular polymerization in the presence of Ziegler-Natta catalysts.
Anion-coordination polymerization is used to obtain stereoregular polymers. The catalyst serves as the matrix on which the polymer chain is built. This allows you to control the process to a greater extent than in other types of polymerization.
1. Li- and K-organic compounds, eg: butyllithium (Bu-Li)
1. The orientation of the monomer molecule with respect to the polarized bond takes place.
2. Introduction (embedding) of a monomer molecule with respect to a polarized bond.
The resulting polymers are stereoregular.
2. Ziegler-Natta catalysts
Initiation takes place under the action of catalysts discovered in 1953 by K. Ziegler and J. Natta, who received the Nobel Prize for this work in 1963. Ziegler-Natta catalysts are complexes of transition metal halides with organometallic compounds: TiCl4 + AlCl (C2H5) 2 .
Ziegler-Natta catalysts are complexes of transition metal halides with organometallic compounds: TiCl4 + AlCl (C2H5) 2.
Method of preparation: 
Two main mechanisms of the polymerization process are suggested: monometallic and bimetallic. Bimetallic involves the participation of both metals, and monometallic - only transient.
Bimetallic mechanism (active center - complex):
The monometallic mechanism (the Cossi-Arlman scheme):
Step 1. Alkylation of a transition metal
Explain the mechanism of inhibition of alternating copolymerization.
Currently, around 150 million tons a year around the world synthetic polymers, with most of this amount so-called large-tonnage polymers are created, and, first of all polymers based on vinyl monomers. And to polymeric materials are presented with new and new requirements, and the quantitymonomers, and as a consequence - types of polymers is limited.One of the simplest and most accessible methods of the new polymeric materials - carrying out of radical copolymerization. The use of controlled synthesis methods for copolymerization. The ability not only to control the molecular mass characteristics polymers, but also to obtain new structures that are inaccessible to the classical RP.
First, we consider a model of copolymerization using the SFRP mechanism.The main feature of the PKP in comparison with the traditional RP is The presence of an equilibrium between the growing ("living") and the inactive ("sleeping")
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state. When copolymerizing two monomers in the framework of the classical model of the Mayo-Lewis end link, the balance between active and 37 Sleeping chains will be determined not by one but by two parallel interactions:
P1Xkd1kt1P1 + X
P2Xkd2kt2P2 + X
Scheme 26
where P1X and P2X are nitroxyl adducts with a macroradical having at the end a link of the first (M1) and second (M2) monomers .In general, the ability of these adducts to dissociate intoradicals differ, and the process of copolymerization can be characterized the effective equilibrium constant Keff, which is a combination of true equilibrium constants
Kef = K1 (P1X) + K2 (P2X),
where, K1 and K2 are the true equilibrium constants for homopolymerization
K1 = ([P1 ·] · [X ·]) / [P1X], K2 = ([P2 ·] · [X ·]) / [P2X],
(P1X) and (P2X) are the proportions of the corresponding terminal units in the copolymer.
In this case, depending on the ratio of the quantities K1 and K2 and on the variation fraction of the adducts P1X and P2X in the course of the reaction, the process can proceed in different modes."Ideal" controlled radical copolymerization
If both the adducts P1X and P2X (Scheme 26) are readily dissociated into radicals, those. K1 ≈ K2 ≥ 10-11 mol / l, then the process proceeds in much the same way as
homopolymerization in controlled mode. A similar situation is realized by copolymerization of CT and its analogs in the presence of TEMPO. When copolymerizing CT and chloromethylstyrene initiated by PB, regardless of the ratio of monomers observed low polydispersity of copolymers (Mw / Mn <1.36) to deep conversions (~ 80%). Copolymerization of CT with vinylpyridine may also occur in controlled mode, since vinylpyridine is similar to CT in polymerization with TEMPO.
The structure of the copolymer macromolecules in the situation under consideration is determined by the usual laws of radical copolymerization. Not there are fundamental obstacles to controlled synthesis with using an ideal pseudo-living copolymerization of statistical, gradient and alternating copolymers. Naturally, in an ideal pseudo-living copolymerization, all chains grow simultaneously and
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Therefore, the copolymer must not only be characterized narrow molecular weight distribution, but also high compositional homogeneity
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