Isotactic polypropylene synthesis

Karmarkar, A. Aggarwal, R Modak, J. Chanda, M. Grafting of m-isopropenyl-a,a-dimethylbenzyl isocyanate onto isotactic polypropylene Synthesis and characterization. J. Polym. Mat. 2003, 20, 101-107. 

Plastomer, a nomenclature constructed from the synthesis of the words plastic and elastomer, illustrates a family of polymers, which are softer (lower hexural modulus) than the common engineering thermoplastics such as polyamides (PA), polypropylenes (PP), or polystyrenes (PS). The common, current usage of this term is reshicted by two limitahons. First, plastomers are polyolehns where the inherent crystallinity of a homopolymer of the predominant incorporated monomer (polyethylene or isotactic polypropylene [iPP]) is reduced by the incorporahon of a minority of another monomer (e.g., octene in the case of polyethylene, ethylene for iPP), which leads to amorphous segments along the polymer chain. The minor commoner is selected to distort... 

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. 

Highly active MgCl2 based catalysts can be obtained by mechanical treatment of mixtures of MgCl2 and Ti-compound. During such treatments the MgCl2 structure undergoes substantial variations which may affect the catalyst performance considerably. A Lewis base can also be added to the systems. The presence of the base is essential for the synthesis of isotactic polypropylene. Both cases will be considered separately. 

A further breakthrough was the synthesis of enantiomeric sterorigid ansa-metallocenes by Brintzinger and co-workers [33] and the discovery by Ewen [34] that such racemic metallocene/methylalumoxane systems generate isotactic polypropylene. It was further found that the metallocene structure determines the polymer structure [35-37]. Again, with these compounds polyolefins such as syndiotactic polypropylene become available on a large scale [38]. Indeed, metallocene/methylalumoxane catalysts offer new prospects for olefin oligomers and polymers [39 2],... 

Early metal-metallocene-alkene polymerization catalysts permit the synthesis of highly isotactic polypropylene . They rely on controlling the stereochemistry of alkene insertion by the use of chiral C2 symmetric metallocenes . Late metal systems for alkene polymerization , and copolymerization of alkenes and CO , have also been developed. 

Dong, J.Y. Wang, Z.M. Han, H. Chung, T.C. Synthesis of isotactic polypropylene containing a terminal Cl, OH, and NH2 group via metallocene-mediated polymerization/chain transfer reaction. Macromolecules 2002, 35, 9352. 

Hagihara, H. Tsuchihara, K. Sugiyama, J. Takeuchi, K. Shiono, T. Copolymerization of propylene and polar allyl monomer with zirconocene/ methylaluminoxane catalyst catalytic synthesis of amino-terminated isotactic polypropylene. Macromolecules 2004, 37, 5145. 

Staudinger predicted a correlation between the physical properties of a polymer and its main-chain stereochemistry as early as 1929. Flowever it was not imtil 1947 that Schildknecht reported the first stereoregular synthetic polymer. - Amidst considerable controversy, he attributed the crystalline properties of a polyfisobutyl vinyl ether) to an ordered stereochemistry, or tacticity, of the polymer backbone. In 1954, research in the field of stereoregular polymers gained a tremendous amormt of momentum when Natta discovered the synthesis of a crystalline isotactic polypropylene using a heterogeneous or-ganometallic catalyst. Since these initial discoveries, the synthesis of polymers of defined stereochemistry... 

The synthesis of polypropylene brought a new scenario and major efforts at that time concentrated on controlling the stereoregularity, synthesizing the most regular isotactic polypropylene, and understanding its polymorphism these efforts have continued for many years. 

The tyqrical structure of metallocene catalyst molecules is reminiscent of that of enzyme molecules, which also catalyze the uniform s5mthesis of a biopolymer molecule. Metallocenes are also capable of determinate control of polymerization reactions of a given tacticity and chain length, for example the synthesis of isotactic polypropylene with a uniform molar mass [4,5],... 

Fig. 3.1 C2v-Ewen s precursor for the synthesis of partially isotactic polypropylene...

Figure 3.8 Synthesis of end-group-functionalized isotactic polypropylene using ZnEt2 or BAZ as chain-transfer agents during propylene polymerization.

Various metal complex systems of Ziegler type are widely applied within industry for the production of high-density polyethylene, isotactic polypropylene, 1,4-c/s-and 1,4- rans-polymers of isoprene and 1,2-poly butadiene, and many other types of copolymers, such as ones based on ethylene and propylene, which could not be produced earlier based on traditional methods of synthesis. 

For isotactic polymers and copolymers the behavior is complex and depends on the method of synthesis and the types of defects that result. For instance, isotactic polypropylene synthesized using Zeigler-Natta catalysts has a quite different defect content from the same polymer synthesized... 

Isotactic polypropylene (iPP) was the first stereo regular polymer to be synthesized. The determination of its crystal structure was instrumental in establishing that the synthesis of the polymer was indeed stereo specific. The TG helical conformation, the 3/1 helix, is the only conformation free of serious steric repulsions in the isotactic chain. Finding this as the observed helix in the crystal... 

In the 1950s, high density PE (HDPE) was marketed. Shortly afterwards in 1953 Ziegler and Natta independently developed a family of stereospecific transition-metal catalysts that led to the synthesis and commercialisation of HDPE as well as isotactic polypropylene... 

These results show that using catalyst 9a for polypropylene synthesis results in isotactic polypropylenes not in the manner of stereoblock polymers, but as iPPs with statistically distributed stereoerrors. 

Shiono, T. Kurosawa, H. Soga, K. Synthesis of isotactic polypropylene functionalized with a primary amino group at the initiation chain end. Macromolecules 1994, 27, 2635—2637. 

---