Bernoullian statistics poly

When these results are compared with those from the polymerization of the other monosubstituted oxiranes (9), it should be emphasized that the partly crystalline fraction of poly(styrene oxide), I, obtained in the presence of the ZnEt2/H20 catalyst is so far the only polyoxirane reported which does not follow Bernoullian statistics. Only one other case, namely that of the polymerization of phenylthiirane by a coordination catalyst system, is known until now which follows first-order Markov statistics (10). 

As an example of the statistical analysis of a tacticity sequence distribution. Table 1.9 gives the experimental distribution for poly(vinyl chloride) derived from Figure 1.19, together with the distribution calculated for Bernoullian statistics with P = 0.456. The agreement is within experimental error up to tetrads. A Bernoullian sequence distribution and a preference for syndio-... 

Preliminary NMR measurements indicate that Bernoullian statistics are also found with 3-substituted poly(3-propiolactones), e.g. poly(3-trichloro-methyl 3-propiolactone). 

The crystallization of racemic di-a-substituted poly(B-propiolactones) is not due to the formation of short isotactic sequences of R or S units since the polymer obeys Bernoullian statistics, as we have discussed above. Its crystallization necessarily involves the incorporation into the crystal of motifs of R and S configurations. 

Several complications are encountered in attempts to interpret the o-aromatic proton resonance patterns of poly(3,4,5-trideuteriostyrene) in terms of its microstructure. Firstly, the resonance patterns cannot be reconciled with a Bernoullian distribution of meso and racemic diads. It seems that the resonance of units centered in rrmr tetrads may occur in the lowest field area rather than in the central (heterotactic) area, as expected. When this assumption is made, the probability of an isotactic (meso) placement in polystyrene, as prepared by free radical methods at 50°, is 0.3, a rather reasonable value. Of course, it is also possible that the microstructure of polystyrene may not be describable by Bernoullian statistics. 

The sequence distribution [31] of hydrophobic comonomer in hydrophobic poly(sodium acrylates) has also been obtained for low molecular weight/high hydrophobe materials. These polymers have been found to obey Bernoullian statistics. 

Statistical copolymers are those in which the monomer sequence follows a specific statistical law (e.g., Markovian statistics of order zero, one, two). Random copolymers are a special case of statistical copolymers in which the nature of a monomeric unit is independent of the nature of the adjacent unit (Bernoullian or zero-order Markovian statistics). They exhibit the structure shown in Figure 6.1. If A and B are the two monomers forming the copolymer, the nomenclature is poly (A-stat-B) for statistical copolymers and poly (A-ran-B) for the random case. It should be noted that sometimes the terms random and statistical are used indistinctly. The commercial examples of these copolymers include SAN poly (styrene-ran-acrylonitrile) [4] and poly (styrene-ran-methyl methacrylate) (MMA) [5]. 

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