Poly butene crystal structure

In the crystal structures of many other isotactic polymers, with chains in threefold or fourfold helical conformations, disorder in the up/down positioning of the chains is present. Typical examples are isotactic polystyrene,34,179 isotactic poly(l-butene),35 and isotactic poly(4-methyl-l-pentene).39,40,153,247... 

Epitaxial crystallization of helical polymers may involve three different features of the polymer chain or lattice. These are (a) the interchain distance (as for stretched out polymers), (b) the chain axis repeat distance, and (c) the interstrand distance - the distance between the exterior paths of two successive turns of the helix. The two former periodicities are normal and parallel to the chain axis direction, and are therefore not usually sensitive to the chirality of the helix (unless the substrate topography is asymmetric and favors a given helical hand). However, the interstrand distance is oblique to the helix axis (it is normal to the orientation of the outer chain path) and therefore has different, symmetric orientations relative to the helix axis for left-handed and right-handed helices (Fig. 2). In other words, epitaxies that involve the interstrand distances are discriminative with respect to helix chirality. This discrimination becomes visible if the crystal structure is based on whole layers of isochiral helices. Such a situation does indeed exist for isotactic poly(l-butene), Form I, that will be considered soon. 

V. Enkelmann, The crystal structure of the low-temperature phase of poly[l,2-bis(p-tolvlsulphonvloxv-methylene)-l-butene-3-vnvlene]. Acta Crvst. B33 2842 (1977). 

Polymorphism is observed relatively frequently in long-chain macromolecules, for which approximately isoenergetic structures exist. The stable crystal form of poly(ethylene), for example, possesses an orthorhombic lattice, but on elongation, triclinic and monoclinic modifications are observed. Three modifications are known in it-poly(propylene) a (monoclinic), P (pseudohexagonal), and y (triclinic). Since the molecules are in a 31 helix conformation in all the modifications, differences in the packing of the chain must be responsible for this polymorphism. The three modifications appear at varying crystallization temperatures. In it-poly(butene-l), however, the various modifications correspond to different kinds of helix, so that variations in conformation must be important (see also Table 5-5). 

The crystal structure of poly[l,2-bis(4-methoxy benzene sulphonyl methyl)-l-butene-3-ynylene] has been determined " since it is central to the topochemical polymerization of disubstituted diacetylenes, e.g. 

Isotactic poly(l-butene) crystallizes from the melt into an unstable modification which is slowly converted into a thermodynamically more stable form. The two modifications differ in helical structure and density therefore, the product undergoes deformation in the course of time [515,516]. For the polymerization of butene the same catalysts are used as for propene. 

In this review the crystal structure and the super-molecular structure of the most used polyolefins is discussed. In particular the latest papers on the morphology of polyethylene, isotactic and syndiotactic polypropylene, isotactic poly(l-butene), and finally isotactic poly(4-methylpentene-l) are summarized and integrated with the fundamental work on the topic. After a short general introduction, the first part of the chapter is dedicated to the analysis of the order at the molecular level (the crystal structure), and the second part deals with the supermolecular structures. 

Spirals on a poly(butene-l) lamellar structure grown from solution are seen in the TEM micrgraphs in Fig. 24 [205]. Spiral growths are frequently found when crystallization is carried out nonisothermally or at high degrees of supercooling. 

It should be pointed out here that the epitaxy caused by special crystallographic interaction provides another efficient way to control the crystal modification of semicrystalline polymers together with molecular chain orientation [83,88,139-142]. As examples, while the crystal structure of isotactic poly(l-butene) (iPB-1) is successfully controlled through using substrates with different crystal structures... 

Zhang B, Yang D, De Rosa C, Yan S, Petermann J. Single crystal structure of form 1 syndiotactic poly(butene-l). Macromolecules 2001 34 5221-5223. 

When Rj is different from R2 in Formula (1.1) the carbon atom is asymmetric and may have d or 7 forms. If all the asymmetric carbon atoms have either d or 7 forms, the polymer chain is said to be isotactic. If these carbon atoms are instead alternating d and 7 , the polymer chain is said to be syndiotactic. If the d and 7 assignments are random along the chain, it is said to be atactic [8,18-20] (see Fig. 1.1). Isotactic polypropylene, poly(butene-l) and poly(4-methylpentene-l) are commercially available. Both isotactic and syndiotactic polypropylene and polystyrene have been synthesized, subjected to extensive investigation. The two isomeric polymers have different crystal structures and their atactic forms do not crystallize. Isotactic and syndiotactic polymers were originally developed by Natta and his coworkers [18, 19] at Milan Polytechnic and Montecatini. In recent years, there has been interest in producing polyolefins with controlled intermediate tacticities [20]. 

LNatta, G. Corradini, P. "The Crystal Structure of Isotactic Poly-1-butene", Makromo. Chem. 1956, 21, 240-244. 

In spite of the similarity of the structure of the monomer units the two corresponding isotactic polymers crystallize in two different chain conformations tiie helix of poly-3-methyl-l-butene contains four monomer units per turn (4/1) with a chain repeat of 6.85 A the helix of poly-4-methyl-l-pentene contains 3.5 units per turn (7/2) and has a repeat of 13.85 A. The copolymers tend to crystallize. Their chain conformation and cross sectional area in the crystal lattice are analogous to those of the homopolymer corresponding to the predominant comonomer. For 4-methyl-l-pentene contents higher than 50% some evidence exists that the system simultaneously contains both chain conformations. 

Three different series of binary blends were prepared by mixing hydrogenated oligo (cyclopentadiene) (HOCP), isotactic polypropylene (iPP), and poly(l-butene) (PB-1), alternatively. The influence of the presence of HOCP, on the morphology, crystallization, melting behavior, and supermolecular structure of... 

Hydrogenated poly(butadiene), an ethylene-butene random copolymer, is often used as die crystallizing block, in di- and triblock copolymers. In this context the copolymer is commonly referred to as polyethylene. This nomenclature can be misleading since it carries the connotation that hydrogenated poly(butadiene) behaves as a homopolymer with respect to crystallization. In fact, it behaves as a typical random copolymer that is located within the structure of an ordered copolymer. 

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