Steric triad composition

One problem encountered in the field is the apparent irre-producibility of the results of different workers, even those in the same laboratory. This is particularly the case with molar mass distribution and steric triad composition. The explanation of these apparent inconsistencies comes with the realization that the mechanisms are eneidic and the polymer properties are primarily determined by independent active centres of different reactivities and stereospecificities whose relative proportions are set at the initiation step, which is completed in the first seconds of the polymerization. The irreproducibilities arise from irreproducibilities in the initiation step which had not been thought relevant. Ando, Chfljd and Nishioka (12) noted that these rapid exothermic reactions tend to rise very significantly above bath temperature (we have confirmed this effect) and allowed for this in considering the stereochemistry of the propagation reaction. However our results show that the influence on the initiation reactions can have a more far-reaching effect. 

The effect on the chain configuration of the polymers was just as drastic. t-Butylmagnesium bromide in toluene solution at 230 produced a polymer of steric triad composition i h s 1 1 1 if initiated at the melting point of toluene, and i h s s 99 0 1 if initator solution at 230 was mixed with monomer solution at 230 K. 

Medium Effect on the Steric Dyad and Triad Composition of Polymers Produced by Initiation and Propagation at 250 and 225 K Using t-Butylmagnesium Compounds... 

The structures of stereoregular and tactic polymers described above are ideal. Real polymers are always irregular they do not have perfect steric or tactic structures. Thus, the mean sequence and composition of steric and configurational diads, triads, etc. must be given by suitable statistical parameters, in analogy to the case for constitutional diads, triads, etc. 

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