Oligomers Schulz—Flory distribution

The sensitivity of the product distribution for small changes of these parameters can also be exploited to our advantage the product distribution can be easily adjusted to changes of the demand for certain oligomers, but only within the limits of Schulz-Flory distributions ... 

Matkovskii et al. also studied ethylene oligomerization. They found that with the homogeneous TiCl —AlC HjCl catalytic system in benzene and at room temperature, the MWD of oligomers was quite similar to the Schulz-Flory distribution and its experimental average values, determined by G.P.C., agree with the theoretical ones derived by analyzing a kinetic model in an almost stationary approximation. 

The compositions of these oligomers can be tailored in part by the choice of organochromium compound, the support, and the reaction conditions. In general, the olefins produced are even-numbered and follow a Schulz-Flory distribution, with one exception nearly all these chromium compounds have a tendency to produce disproportionately more 1-hexene than the other a-olefins. Indeed, some organochromium compounds produce only 1-hexene, and no other olefin or polymer product. 

In all the above ethylene oligomerizations, Schulz-Flory distributions of oUgomers are observed which can be quantified by the a value, which represents the probability of chain propagation [117, 118]. The magnitude of a can be experimentally determined by the ratio of two oligomer fractions Eq. (5.1). The a value is usually preferred to be in the range of about 0.6 to about 0.8 to make a-olefins of the most commercial interest... 

The nickel-catalyzed Shell higher olefin process (SHOP) is of major industrial importance [9,11]. Ethylene is converted to a-olefins with a statistical distribution in which the lower oligomers are favored (so-called Schulz Flory distribution). This is carried out at 80-120 °C and 70 140 bar in the presence of a nickel catalyst with phosphine ligands such as Ph2PCH2COOK. The product mixture is separated into C4 io, C12-18, and C20+ fractions by distillation. 

Figure 6.16.2 Schulz-Flory distribution of ethylene oligomers. Mass and mol fractions are given as a function of the ratio of rate of insertion (ins) and rate ofelimation (eli) (insieli is equal to 1//3).

If the average molecular weight of the total oligomer is experimentally available, its monomer dependence allows one to decide which of the two reaction schema (set a or set b) is applicable. In either case, a normal molecular weight distribution (Schulz-Flory distribution) results. This means that the weight fraction nip of oligomer of degree of... 

The catalyst systems so far reported for the oligomerization of ethylene to linear a-olefins appear to operate all according to the same reaction mechanism which, in the absence of disturbing side reactions, leads to a Schulz-Flory distribution of molecular weights. This fixes the optimal weight fraction of oligomer of a particular molecular weight... 

We have arrived at a similar conclusion concerning an additional coordination of a double bond on the grounds of the molecular weight distribution of the oligomers in the initial stage of the reaction whidh corresponds to a Schulz-Flory distribution controlled by addition and transfer reactions. As well the formation of oligomers of cyclooctene and cyclododecene and the monomer-polymer equilibrium in the case of the metathetical polymerization of cyclopentene can be made plausible by this concept (Fig. 8). 

The oligomers obtained with these systems follow a Schulz-Flory type distribution. The nickel catalyst complexes can be divided into two groups nickel(ll) compounds modified with alkyl or hydride main-group metal derivatives (Ziegler-Natta type catalyst) and chelated nickel compounds with a Ni-C bond. 

A similar trend is observed for the polydispersities of the formed PPEs. At the beginning the polydispersity increases fast, to level off after about 24 h at a value of approximately 3—5. These values are higher than for a classic Flory—Schulz distribution, but it may be an effect of increased reactivity of the larger oligomers toward further metathesis. How-... 

---