Polypropylene, syndiotactic

Syndiotactic polypropylene became commercially available about ten years ago with the advent of single-site catalysts. Unlike its atactic and isotactic counterparts, its manufacture presented serious challenges to polymer scientists and engineers. Even under the best conditions, its syndiotacticity rarely exceeds 75%, based on pentad sequences. It typically has both a lower melting point (approximately 138 °C relative to approximately 155 to 160 °C) and density (0.89 g/cm3 relative to 0.93 g/cm3) than isotactic polypropylene. Syndiotactic polypropylene crystallites have a much more complex structure than the isotactic form, which impedes its crystallization. Therefore, in general, the syndiotactic form of polypropylene crystallizes very slowly. 

The main characteristics of most of these heterogeneous catalysts is that, due to the size and shape of the complex, the insertion is only possible for one particular spatial orientation of the monomer, which, in the case of an asymmetric monomer like propylene, leads to a good control of tacticity. While use of Ti-based catalyst can lead to isotactic polypropylene, syndiotactic polypropylene is obtained using V-based catalysts. 

We will then examine other flexible polymer crystallization instances which may be interpreted, at least qualitatively, in terms of the bundle model. We will concentrate on crystallization occurring through metastable mesophases which develop by quenching polymers like isotactic polypropylene, syndiotactic polypropylene etc. In principle also hexagonal crystallization of highly defective polymers, and order developing in some microphase-separated copolymer systems could be discussed in a similar perspective but these two areas will be treated in future work. A comparison between the bundle approach and pertinent results of selected molecular simulation approaches follows. 

Being acquainted with the structure of poly(a-olefin)s, one may reasonably explain some of the differences in their physicochemical properties. For example, isotactic polypropylene, the chains of which in the helical conformation can be closely packed, has rather a high density (0.92-0.94 g/cm3) and melting point (175°C) and is insoluble in low-boiling aliphatic hydrocarbons at boiling point. Syndiotactic polypropylene, consisting of chains in the form of binary helices, which cannot be packed so closely as in the previous case, has a density of 0.89-0.91 g/cm3 and a melting point of 135°C, which is 40 k lower from that of isotactic polypropylene syndiotactic polypropylene is also moderately soluble in... 

V(acac)3-A1(C2H5)2C1 a propylene —78 °C, toluene polypropylene syndiotactic 1.05-1.20 110-111)... 

Poly(2,6-dimethyl-l,4-phenylene ether) 298 18.1 Polypropylene, syndiotactic 298 17.6... 

Research Associate, Amoco Chemical Company, Naperville, Illinois Polypropylene, atactic Polypropylene, elastomeric (stereoblock) Polypropylene, syndiotactic... 

Polypropylene, isotactic Polypropylene, syndiotactic Poly (tetrafluoroethy lene)... 

Syndiotactic polypropylene Syndiotactic polystyrene Synpol Technyl D... 

Keywords epitaxy, isotactic polypropylene, syndiotactic polypropylene, crystal structure, crystal polymorphism, helical hand, nucleating agents, AFM, a-phase, 3-phase, lamellae. 

Syndiotactic Polypropylene. Syndiotactic polypropylene (sPP) is a crystalline homopol5Tner with alternating stereochemistry at each successive methine carbon in the chain (Fig. 11). 

Figure 6 Different helical conformations adopted by macromolecules in the crystalline state. The molecular helices are shown for PE, isotactic polypropylene, syndiotactic polypropylene, and polyethylene oxide from left to right, respectively. The type of the helix is denoted by the number of monomers per integer number of turns shown in subscript.

Additionally, metallocene catalysts enable the design of catalysts for tailored polyolefins due to the intrinsic nature of the single site. Actually, new polymers which could never have been produced by conventional Ziegler-Natta catalysts, i.e., syndiotactic polypropylene, syndiotactic polystyrene, long chain branched polyolefins, cyclo-olefin polymer, and styrene copolymers, can be obtained by metallocene catalysts. This upcoming new S curve in the polyolefin development cycle means the evolution of new type of polyolefins. 

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