High molecular weight polymers styrenes

The polymerization of styrene by Zr (benzyl) 4 has the characteristics of producing high molecular weight polymers by a very slow polymerization process. This can be reasonably explained by a slow initiation process followed by a fast propagation reaction. These two processes are probably chemically similar but differ significantly in rate for structural reasons. 

Quantitative polymerizations of butadiene and copolymerizations of butadiene with styrene to high molecular weight polymers have been obtained. Plots of In (M0/Mt)versus time are linear, indicating a first order dependence on monomer. 

Reactivity Is typical of an acrylamide. For example, compound 1 shows essentially 1 1 copolymerizablllty with butyl acrylate. Copolymerizablllty has also been demonstrated with styrene, other acrylates and methacrylates, vinyl acetate (VAc), VAc/ethylene and vinyl chlorlde/ethylene. High molecular weight polymers and copolymers remain soluble. Indicating any chain transfer to polymer, e.g. through abstraction of the acetal hydrogen. Is minor. 

Redox polymerizations are usually carried out in aqueous solution, suspension, or emulsion rarely in organic solvents. Their special importance lies in the fact that they proceed at relatively low temperatures with high rates and with the formation of high molecular weight polymers. Furthermore, transfer and branching reactions are relatively unimportant. The first large-scale commercial application of redox polymerization was the production of synthetic rubber from butadiene and styrene (SBR1500) at temperatures below 5 °C (see Example 3-44). 

Diethyizinc is not an active catalyst for polymerization of ethylene oxide and propylene oxide, but gives a high molecular weight polymer from styrene oxide (78) and a copolymer from styrene oxide and propylene oxide (79). This behavior is interpreted by assuming that styrene oxide easily reacts with diethyizinc to give a catalytically active species Zn[OCH2CH PhEt]2 (79,80). 

This behavior is an evidence of the small-scale mechanism of the molecular motion of polystyrene in the electric field each monomer unit of the polymer chain is oriented virtually independently of other units, just as in the monomeric styrene. Equation (99) shows that for high molecular weight polymers K is proportional to S, This accounts for the much higher values of K for rigid-chain polymers than for flexible-chain polymers (Table 13) since the corresponding values of S are of order of m nitudes 10—10 for flexible and approximately unity for i%id polymers in the electric field. 

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