Branch distribution lower activation temperature

Lower activation temperatures are usually preferred in commercial operations, despite the lower activity. The corresponding redistribution of sites results in improved polymer physical properties. An example is shown in Table 12, which is a list of the ESCR values, the resistance to chemical attack, of several ethylene-butene and ethylene-hexene copolymers. These copolymers were made at constant MI and density with Cr/ silica catalysts activated at various temperatures. The measured ESCR value decreases as the activation temperature is raised. This change results in part because the MW distribution is narrowed, but more so because the longest chains contain less branching.13... 

The oil furnace process involves a liquid hydrocarbon, usually a heavy petroleum oil, which is injected, sprayed, and mixed with preheated air and natural gas in a reactor. Part of the hydrocarbon is burned to maintain the reaction temperature ranges of 1,450 to 1,800 °C and the remainder is converted to carbon black. This process has a lower residence time and yields a narrower distribution of carbon black aggregate sizes, higher surface activity, and open aggregates (branched or grapelike (bulky)). 

Porosities were analyzed by use of the Kelvin equation on the adsorption branch. Assuming a cylindrical pore model the analysis yields an average pore radius distributed around a peak at 2 nm, i.e. at the very low end of the mesopore [ref. 4] range. From literature there has been much evidence that the lower closure point of the hysteresis loop occurs above a certain critical relative pressure characteristic of the adsorptive at a particular temperature for nitrogen at 77 K this critical relative pressure is about 0.45 [ref. 5]. In the present experiments the related hysteresis loop is therefore rather unusual. It may result either from a distortion of the structure of the adsorbent which is difficult to reverse or from an activated passage of the nitrogen molecules. This may have some bearing on the type of... 

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