Isotactic polypropylene rates

Eastman Chemical has utilized a unique, high temperature solution process for propylene polymerization. Polymerization temperatures are maintained above 150°C to prevent precipitation of the isotactic polypropylene product in the hydrocarbon solvent. At these temperatures, the high rate of polymerization decreases rapidly, requiring low residence times (127). Stereoregularity is also adversely affected by high temperatures. Consequentiy, the... 

Metallocene isotactic polypropylenes (MET.PP) are accessible with different melting points under the commercial range of melt flow rate (Fig. 11). The variation of melting points in these polymers is linked with the presence of different lengths of isotactic sequences. Mechanical properties of polypropylene... 

In the crystallization of isotactic polypropylene from the melt, the number and size of the spherulites (and hence the rate of crystallization) can be influenced by the addition of certain nucleating agents.The smaller the spherulites, the greater is the transparency of the polypropylene film.The mechanical properties can also be affected in some cases. 

The first work reported in this area was an investigation of isotactic polypropylene which was fatigued at a rate of 10 hz with an elongation of one to five percent. The spectra showed no shifts in frequency but reversible intensity changes were observed. The data were interpreted in terms of the presence of a smectic-like structure as a result of the cyclic stress 304i 305>. 

The oxidation rate of 0.5 gram atactic polypropylene with 0.02M cobalt acetate in 10 ml. of a 1/1 mixture by volume of chlorobenzene and acetic acid increases from 2.7 X 10"4 to 2.76 X 10"8 mole kg. 1 sec."1 in the presence of 0.04M sodium bromide. The rate of powdered isotactic polypropylene under the same conditions increases only from 2.05 X 10"8 to 2.45 X 10"3 mole kg. 1 sec. 1 in the presence of sodium bromide. 

Under the conditions used these compounds were the most active derivatives of pyrocatechol. High activity was found also with two derivatives having acyl groups (Table I). The decrease in the rate of oxygen absorption in isotactic polypropylene in the presence of 4-caproyl-, 4-lauroyl-, and 4-stearoylpyrocatechol compared with pyrocatechol is shown by Fic (10). The activity of 4-alkyl and 4-acyl derivatives of pyrocatechol found at high temperatures in polypropylene differs from the published data on the activity of 4-dodecyl- and 4-lauroylpyrocatechol in lard (39) compared with pyrocatechol, the relative activity decreased in the presence of the first substance by 15%, and it decreased in the presence of the second by as much as 68%. Tamura and co-workers... 

A new technique for following rapid rates of crystallization. II. Isotactic polypropylene. Polymer 3, 35—42 (1962). 

The steric configuration is extremely important in the polymer. Only isotactic polypropylene (iPP) has the properties necessary for forming fibers. The molecules are cross-linked only by Van der Waals forces, so it is important that they pack as closely as possible. The isotactic molecules form a 3, helix, as shown in Fig. 12.21,16 and exhibit a high crystallization rate. The atactic molecules, shown in the figure, do not pack well, and although the syndiotactic molecules can pack better and crystallize, this configuration is not a normal product of commonly used catalyst systems. 

U.V. Makedonov, A.Z. Margolin, H.la. Rapoport, LS. Shibriaeva About the reasons of the change of effective constants of the rate of reactions of continuation and chains breaks in the period of oxidation induction of isotropic and oriented isotactic polypropylene////zg/zzzzo/eczz/z7r compounds (1986), 28 (A), No 7, 1380-1386 (in Russian). 

It is to be noted that Ti, A1 and ethyl benzoate are present in nearly equal molar ratio. Results of propylene polymerization with this type of catalyst showed that ethyl benzoate enhanced the rate of formation of isotactic polypropylene, while it decreased the rate for atactic polypropylene. Ethyl benzoate seems to make the catalytic sites sterically more specific. 

To study cooling rate effects which might affect the supramolecular self-assembly of trisamides in i-PP, we investigated the influence of the processing conditions on the electret performance. Isotactic polypropylene containing 0.09 wt% of compound 1 was chosen for these experiments. After compression molding, the films... 

Polypropylene is a polyolefin found in high concentrations in the plastic waste stream. Of the different types of PP, isotactic polypropylene is the one most widely used on a commercial scale and so is the type predominant in plastic wastes. Compared to PE, the backbone of the PP molecule is characterized by the presence of a side methyl group at every second carbon. This fact implies that half of the carbons in a PP chain are tertiary carbons and so, as a consequence of their higher reactivity, PP is thermally degraded at a faster rate than PE. Thus, as can be seen in Figure 4.7, the PP weight loss in TGA measurements starts at a lower temperature compared to both HDPE and LDPE. 

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