Catalyst fragmentation

The final variable to be mentioned here is the presence of impurities. These may be metallic fragments residual from Ziegler-type processes or they can be trace materials incorporated into the polymer chain. Such impurities as catalyst fragments and carbonyl groups incorporated into the chain can have a serious adverse influence on the power factor of the polymer, whilst in other instances impurities can have an effect on aging behaviour. 

Is a Cluster the Real Catalyst Fragmentation and Aggregation Phenomena... 

We wanted to be able to correct measurements of dielectric loss (conductance) and dielectric constant of polymerizing styrene solutions for whatever contribution arose from the dead polystyrene present in the solutions. What better way to make polystyrene that was free of all catalyst fragments and polar groups than to irradiate pure, dry styrene Using the same exhaustive drying technique that we were developing for our a-methylstyrene studies, we prepared a batch of pure, dry styrene. This was then to be irradiated under such conditions that approximately 15% conversion to polymer would occur. 

No foreign materials or catalyst fragments need be incorporated into the polymer. This can be important in electrical or medical applications. 

Steps (b) and (c) remove S02 and S03 from all the catalytic oxidation equipment (avoiding corrosion). They also cool equipment and catalyst slowly (avoiding thermal stress and catalyst fragmentation). 

Industrial catalyst bed gas pressure varies slightly between acid plants depending on altitude. It also tends to increase slightly over time as catalyst beds become clogged with dust and catalyst fragments. 

In Figure 22(a), an approximately 2-mm catalyst fragment shows an evidently similar peripheral penetration of alloy at X40 magnification. In Fig. 22(b), the penetration is increased toward the interior. At the highest pressure, 50 atm, there is substantial penetration throughout the whole interior, and Fig. 22(c) shows behavior exactly similar to the virtual section in Fig. 21(c). Also clearly evident in Fig. 22(c) are dark spaces identifiable with unpenetrated pore voids. These have an apparently similar appearance and spatial distribution to the dark unpenetrated hypothetical voids shown black in Fig. 21(c). 

Catalyst Fragment of AC Monomer Propagation rate constant in l/(mol X s) Ref. 

Certain catalysts, such as the 7r-allyl nickel halides, which are effective for butadiene, exist in dimeric form and are converted into active species by dissociation. Partial dissociation followed by addition of monomer to the active catalyst fragments would result in the rate of polymerization being proportional to [C2] [M], where C2 represents the dimeric catalyst species. 

Method of preparation incorporation of catalyst fragments, double bond formation... 

The insertion reaction has both cationic and anionic features. There is a concerted nucleophilic attack by the incipient carbanion polymer chain end on the a-carbon of the double bond of the monomer together with an electrophilic attack by the cationic counterion (G) on the alkene tt-electrons. The catalyst fragment acts essentially as a template or mold for the orientation and isotactic placement of incoming successive monomer units. Isotactic placement occurs because the Initiator fragment forces each monomer unit to approach the propagating center with the same face. This mechanism is referred to as catalyst site control or enantiomorphic site control. 

Buried within the polymer, the dispersed catalyst fragments are difficult to see, even with the best microscopy. Nevertheless, one can observe... 

FIGURE 52 Large catalyst fragment obtained by plasma ashing of polymer. 

TABLE 14 Some Typical Dimensions Involved in the Catalyst Fragmentation Process... 

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