Preparation of Isotactic Polypropylene

After 2 h the polymerization is terminated by addition of 20 ml of 2-propanol, and stirring continued for another 30 min at 60 °C the reaction mixture decolorizes and becomes white. After filtration using a Buchner funnel and several washings with warm petroleum ether the polymer is dried to constant weight in vacuum at 70 °C. Yield 29.5 g. 

The polypropylene so obtained has a high molecular weight and is crystalline.The proportion of isotactic polymer, determined by extracting with heptane for 10 h in a Soxh-let apparatus, is 98.5%. Isotactic polypropylene shows similar solubility behavior to polyethylene, but has a higher melting point (crystalline melting range 165-171 °C). 

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The above Cp2MQ2 species are immediate precursors for highly active Ziegler-Natta catalysts for die preparation of isotactic polypropylene with methylalumoxane as a cocatalyst die racemic mixtures can be directly employed in stereospecific propylene polymerizations (see Section IV,D,2) (225,227,228) the enantiomers are employed in asymmetric hydrooligomerizations ofa-olefins... 

TiCl4/MgCl2 catalysts may be used for the polyethylene synthesis, but not for the preparation of isotactic polypropylene. In fact, although these catalysts are highly reactive for the propylene polymerization, they are not stereospecific enough to give a commercially interesting product. 

Only dibutyl H-phosphonate has been reported to be used directly (together with other cocatalysts) for the preparation of isotactic polypropylene [125], Most of the other catalysts based on dialkyl H-phosphonates comprise of their metal and anunonium derivatives. Sodium dialkyl phosphite is used as a catalyst for the cyclotrimerization of 2,4-toluenedi-isocyanate with phenyl, m-chlorophenylene or a-naphthylisocyanates, forming oligomeric diisocyanates containing triisocyanurate cycles [126]. 

AveUa, M., Cosco, S., and Errico, M. E. 2005. Preparation of isotactic polypropylene/organoclay nanocomposites by solution mixing methodology Structure and properties relationship s. Macromolecular Symposia 228 147-154. 

Yang, K., Huang, Y, and Dong, J.-Y. 2007. Efficient preparation of isotactic polypropylene/ montmorillonite nanocomposites by in situ polymerization technique via a combined use of functional surfactant and metallocene catalysis. Polymer 48 6254-6261. 

The preparation of syndiotactic polypropylene is carried out in the 195-230 K range, while the preparation of isotactic polypropylene takes place at 295-365 K if the catalyst is suspended and at 380-425 K in the presence of a homogeneous catalyst. These conditions are very mild compared to those for radical polymerization which is carried out at 295-470 K and 100-300 MPa. Ziegler-Natta catalysts are also utilized in polymerization of 1,3 dienes and cycloalkenes, for example, butadiene, isoprene, cyclobutene, cyclopentene, and dicyclopentadiene. Conjugated dienes may form the... 

The three different stereochemical forms of polypropylene all have somewhat different properties, and all can be made by using the right polymerization catalyst. Propylene polymerization using radical initiators does not work well, but polymerization using Ziegler-Natta catalysts allows preparation of isotactic, syndiotactic, and atactic polypropylene. 

The program just described, for Rietveld analyses using generalized coordinates, has been used in the structural analysis of isotactic polypropylene recently undertaken both with x-ray and with neutron powder diffraction data. We believe this analysis (Immirzi, in preparation) to be the first Rietveld analysis of a polymer done from x-ray data. Rietveld analyses of polymers from neutron data have been done but, at least in the polyethylene case reported by Willis and co-workers (15), there was no use of generalized coordinates. 

Results of X-ray Rietveld analyses of isotactic polypropylene (excerpted from Imnirzi, in preparation)... 

Elastomeric polypropylenes with thermoplastic behavior can be prepared from conformationally dynamic metallocenes such as bis(2-arylindenyl)zirconium dichlorides. These can exist in two conformations in the course of the chain lifetime a chiral rac isomer which is stereodirecting and an achiral meso isomer which is aspeciflc. The resulting polymer consists of blocks of isotactic polypropylene alternating with runs of atactic material (equation 12). 

About 45% of the propylene produced is used for the production of isotactic polypropylene. About 10% fractions of the total are consumed for each of acrylonitrile production, the preparation of the oxo-alcohols, for propylene oxide, and for cumene (isopropylbenzene) production. 

Figure 3.5 Lattice parameters of isotactic polypropylenes randomly copolymerized with various proportions of butene-1. The crystal is monoclinic, with the chain helical axis in the c direction. The data include the results (in solid symbols) obtained with single crystals prepared from solution (Cavallo et al.]5) and those (in open symbols) obtained with melt crystallized samples (Tumer-Jones16).

Varga, J. (2002). Beta-modification of isotactic polypropylene Preparation, structure, processing, properties, and apvplication.. Macromol Sci, Phys. B., Vol. B41, Issue 4-6, pp.1121-1171. 

A) DSC heating curves of isotactic polypropylene, prepared by temperature gradient annealing, as a function of scanning rate (1) 1.25 (11) 2.5 (111) 5 ... 

Lin, C.W., Ding, S.Y. and Hwang, Y.W. 2001. Interfacial crystallization of isotactic polypropylene molded against the copper surface with various surface roughnesses prepared hy an electrochemical process. J. Mater. Sci. 36 4943 948. 

Bikiaris, D. N., Papageoigiou, G. Z., PavUdou, E., Vouroutzis, N., Palatzoglou, P, and Karayannidis, G. P. 2006. Preparation by melt mixing and characterization of isotactic polypropylene/ Si02 nanocomposites containing imtreated and surface-treated nanoparticles. Journal of Applied Polymer Science 100 2684—2696. 

Ljungberg N, Cavaille J-Y, Heux L (2006) Nanocomposites of isotactic polypropylene reinforced with rod-like cellulose whiskers. Polymer 47 6285-6292 Lu Y, Weng L, Cao X (2005) Biocomposites of plasticized starch reinforced with cellulose crystallites from cottonseed linter. Macromol Biosci 5 1101-1107 Lu J, Wang T, Drzal LT (2008) Preparation and properties of microfibrillated cellulose polyvinyl alcohol composite materials. Compos Part A 39A 738-746 Magalhaes WLE, Cao X, Lucia LA (2009) Cellulose nanocrystals/cellulose core-in-shell nanocomposite assemblies. Langmuir. doi 10.1021Aa901928j Malainine ME, Mahrouz M, Dufresne A (2005) Thermoplastic nanocomposites based on cellulose microfibrils from Opuntiaficus-indica parenchyma cell. Compos Sci Technol 65 1520-1526 Marchessault RH, Sundararajan PR (1983) Cellulose. In Aspinall GO (ed) The polysaccharides. Academic, New York... 

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