I.W. Bassi

CRYSTAL STRUCTURE OF ISOTACTIC POLYSTYRENE

ABSTRACT The crystal structure of isotactic polystyrene is described in this paper. The unit cell as determined from the X-ray diffraction spectra of oriented samples is rhombohedral, and its constants referred to hexagonal axes are: a = 21.9 ± 0.1 A , c = 6.65 ± 0.05 A ( chain axis ) Z = 18 ; Space group R 3 c or R 3 ¯ c .

CRYSTAL STRUCTURE OF ISOTACTIC POLY-α-BUTENE

ABSTRACT The crystal structure of the most stable crystalline modification of isotactic poly-α-butene was examined by X-ray diffraction spectra of oriented samples. The unit cell is rhombohedral and its constants, referred to hexagonal axes, are: a = 17.7 ± 0.1 A , c = 6.50 ± 0.05 A ( chain axis ) Space group R 3 c or R 3 ¯ c , Z = 18.

Crystal and molecular structure of 1,4‐bis(chloroacetyl)‐trans‐2,5‐dimethylpiperazine, a model compound of poly(trans‐2,5‐dimethyl‐1,4‐piperazinediylfumaroyl)

The molecular and crystal structure of 1,4-bis(chloroacetyl)-trans-2,5-dimethylpiperazine synthesized by us, was determined from X-ray diffractometer data. The structure was solved by Patterson and Fourier methods and refined by least-squares techniques to R 0,065 for 1081 independent reflections. The crystals are monoclinic, space group P21/n, with Z = 2 in a unit cell of dimensions: a = 9,486 (6), b = 9,139 (6), c = 7,036 (5) A, β = 95,73 (10)°, the numbers in parentheses being the estimated standard deviations refering to the last significant digit. The trans-2,5-dimethylpiperazine ring is in a flattened-chair conformation with the side methyl groups in axial position. The atoms of the amide are nearly coplanar. It seems to be proved that the structure of the trans-2,5-dimethylpiperazine ring in poly(trans-2,5-dimethyl-1,4-piperazinediylfumaroyl) is similar to that found for 1,4-bis(chloroacetyl)-trans-2,5-dimethylpiperazine.

CRYSTAL STRUCTURE OF THE COMPLEX (C5H5)2TiCl2Al(C2H5)2

Publisher Summary This chapter discusses the synthesis of a soluble crystallizable complex containing titanium and aluminum showing catalytic activity in the polymerization of ethylene. It also describes an experiment in which the two different metal atoms contained in the crystallizable complex were joined by the bridges of the same type as the one present for instance in the monochlorodimethylaluminum dimer. The number of molecules contained in the unit cell is four, and the possible space groups are Pnma. The space group Pnma requires that the molecule contains a mirror plane. The chapter illustrates the Patterson projection on the a–b plane of the interatomic vectors showing a concentration of the highest peaks along the lines γ = 0 and γ = ½ presents the hypothesis that heavy atoms are contained in the γ = ½ plane.

THE CRYSTALLINE STRUCTURE OF ISOTACTIC POLY-α-BUTENE

ABSTRACT The structural properties of modification I of poly-α-butene are studied by electron-ray and X-ray diffraction spectra. The macromolecule of isotactic poly-α-butene, crystallized in this modification, shows a threefold helix symmetry, with a repetition period of 6·5 A. The unit cell is rhombohedric, and its constants referred to the hexagonal axes are: a = 17·7 A, c = 6·50 A. Two space-groups R3c or R 3 ¯ c are possible. The number of monomeric units contained in the unit cell is 18; each macromolecule is surrounded by three enantiomorphous macromolecules. An interesting phenomenon of statistical vicariance, concerning the R 3 ¯ c space-group is described here. It is possible that around each of the six threefold screw-axes, contained in the unit cell, isomorphous anticlined macromolecules may also vicariate.

X-RAY CHARACTERIZATION OF SOME NEW ISOTACTIC POLYMERS

ABSTRACT The results of the X-ray characterization of some new isotactic polymers are reported here. They include also some fluorinated polymers which can yield fibres: (a) Poly-para-fluorostyrene (identity period 8·30 A; helix 4 1 ) (b) Poly-ortho-fluorostyrene (identity period 6·63 A; helix 3 1 ) (c) Poly-ortho-methyl-para- fluorostyrene (identity period 8·05 A; helix 4 1 ) and poly-α-vinylnaphthalene (identity period 8·10 A; helix 4 1 ) and polyallyltrimethylsilane (identity period 6·50 A; helix 3 1 ) The reasons why the above-mentioned polymers assume different conformations are also reported. The shape of their chains and their helix type having ternary or quaternary symmetry, depending on the hindrance and the mode of packing in the crystalline lattice, confirms their isotacticity and the stereoselectivity of their method of preparation.

THE CRYSTALLINE STRUCTURE OF ISOTACTIC 1,2-POLYBUTADIENE

ABSTRACT The crystalline structure of isotactic 1,2-polybutadiene is studied in this paper. The chain structure and the mode of packing of the chains among themselves is substantially analogous to that found by the same authors in isotactic poly-α-butene. The only difference is in the orientation of the side group, which satisfies in both cases the principle of the maximum separation of simple bonds.

THE CHAIN STRUCTURE OF CRYSTALLINE POLYVINYLISOBUTYL ETHER

ABSTRACT The chain structure of polyvinylisobutyl ether prepared by cationic catalysis according to Schildknecht et al. is discussed in this paper. The X-ray data are interpreted with the aid of molecular Fourier transforms. It was possible to conclude that the polymer in the crystalline state is isotactic, that is: all the tertiary carbon atoms have the same steric configuration, with a ternary helix-type symmetry of the chain (of the Bunns (AB)3 type). It has been observed that a complete analogy exists between the molecular structure of crystalline polyvinylisobutyl ether and that of isotactic poly-5-methyl-hexene-1. The latter was prepared by anionic catalysis.

CRYSTAL STRUCTURE OF POLY-O-FLUOROSTYRENE

ABSTRACT The X-ray diffraction spectra obtained from oriented fibres of poly-o-fluorostyrene are very similar to those obtained from fibres of isotactic polystyrene. The diffraction spectra are interpreted on the basis of a rhombohedral unit cell; its constants, referred to hexagonal axes, are: a = 22.15 ± 0.10 A , c = 6.63 ± 0.05 A ( chain axis ) Z = 18 ; space group R 3 c or R 3 ¯ c .

POLYMORPHISM OF CRYSTALLINE TITANIUM TRICHLORIDE

ABSTRACT Once the existence of different stereospecific activities of TiCl 3 was observed depending on its method of preparation, the supposition of different polymorphous modifications of the compound could be advanced. The methods of preparation of the three polymorphous modifications of TiCl 3 , (a) TiCl 3 α, (b) TiCl 3 β, (c) TiCl 3 γ, are described here; these modifications have been subsequently analysed by X-ray methods. The X-ray spectrum of the α-modification, as already described by Klemm and Krose, Z. Anorg. Chem., 253, 209 (1947), can be interpreted on the basis of a layer lattice, which can originate from a hexagonal close-packing of the chlorine atoms, in which the titanium atoms are arranged in layers, placed at every second layer of the chlorine atoms. The elementary unit cell of this modification has constants of a = b = 6·12 A, c = 17·50 A, γ = 120°, space group R 3 , the coordinates of the chlorine atoms are 1/3; 0; 0·079; those of titanium are 0; 0; 1/3 ( Fig. 1 ). The X-ray spectrum of the β modification can be interpreted on the basis of a hexagonal unit cell, having constants of a = 6·27 A, c = 5·82 A; space group C 6/ mcm; the structure of such a modification is derived from a hexagonal close-packing of the chlorine atoms, by the gathering of the TiCl 3 molecules in rows which are parallel to the three-fold axis; the coordination of the halogen atoms around the titanium is still octahedral, but the way in which the titanium atoms are arranged among themselves is completely different. The coordinates of the Ti atoms were found in X = 0, Z = 0; those of chlorine in X = 0·315, Z = ¼ ( Fig. 2 ). The X-ray spectrum of the γ modification was not interpreted in this paper; however, it may be said that it is derived as in the α-modification, from a layer lattice.