Isotatic polymers

Polymers wherein all adjacent asymmetric carbon atoms over the length of the Polymer chain have the same space configuration are known as isotatic polymers. 

Figure 10.24. Bercaw catalysts for syndiotactic polymer and isotatic polymer...

The very large dipole moment of polymers results in strong intermolecular forces in solution. Atactic and isotatic polymers have different dipole moments. The dipole moment of the atactic poly(vinyl isobutyl ether) is 10% lower than that of the isotactic form, showing that the isotactic polymer adopts a more ordered structure with group dipoles tending to align parallel to each other. 

The polymerization of butadiene and isoprene with an organometallic compound-transition metal compound Ziegler-Natta type catalyst can lead to polymers wdth a microstructure which is all cis-1,4-, trans l,4-, isotatic 1,2- (or 3,4-), syndiotactic 1,2- (or 3,4-), or a combination of two or more of these structural imits. The polymer microstructure may be dependent upon the ratio of the catalyst components, the temperature, and the reaction medium. 

J.E. Volponi, L.H.I. Mei, and D. dos Santos Rosa, The use of differential photocalorimetry to measure the oxidation induction time of isotatic polypropylene, Polym. Testing 2004, 23, 461 165. 

The corresponding 13C-NMR spectrum is shown in Fig. 8.3. One set of lines (more abundant) is identical with the spectrum of the polymer obtained from the optically pure enantiomer. Thus it was concluded that in the polymer prepared from racemic DBO two sets of signals corresponding to isotatic and syndiotactic dyads are present. 

The most recent catalysts for syndiotactic polypropylene are complexes, like i-propyl(cyclopen-tadienyl-l-fluorenyl)hafiiium dichloride with methyl aluminoxane. Another, similar catalyst is /-propyl(/7 -cyclopentadienyl- / -fluorenyl)zirconium dichloride with methyl aluminoxane. These catalysts yield polymers that are high in syndiotactic material (the zirconium-based compound yields 86% of racemic pentads)Commercial production of syndiotactic polypropylene is in the planning stage. What catalytic system will be used, however, is not known at this time. Some of the properties of the two isomers, isotatic and syndiotactic polypropylenes, are compared in Table 5.5. 

B De Roover, J Devaux, R Legras. Maleic anhydride homopolymerization during melt functionalization of isotatic polypropylene. J Polymer Sci Polymer Chem 34 1195-1202, 1996. 

Other polymers have other growth directions, e.g. monoclinic isotatic polypropylene grows faster along the a-axis. Similar behaviour is observed with... 

They can polymerize vinyl monomers regardless of the monomers molecular weight or stress hindrance they produce very uniform polymers of narrow molecular weight distribution they can polymerize a olefins with very high stereoregularity to give isotatic or syndiotactic polymers. 

In the following subsections are given examples of the use of Raman spectroscopy to obtain this orientation information for three polymers isotatic polypropylene (iPP), high-density polyethylene (HDPE) and poly(ethylene terephthalate) (PET). 

Due to the industrial importance of the process, many semicrystalline polymers have been investigated polyethylene [116-121], isotatic polypropylene [122-127], polybutene-1 [128], polyoxymethylene (or poly acetal) [129-131], polyamide 6 [132], poly(phenylene sulphide) (PPS) [133], and so on. 

Figure 11.10 Comparison of experimentally determined growth rates of spherulites of i-polystyrene with ( ) experimental (— ) theoretical values. (From J. Polym. Sci. Polym. Phys. Ed., 21, Kennedy, M. A., G. Turturro, G. R. Brown, and L. E. St.-Pierre Retardation of spheralitic growth rate in the crystallization of isotatic polystyrene due to the presence of a nucleant, Copyright 1983 hy John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc.)...

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