G. Natta

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 structures of odd and even trans polyalkenamers

Abstract The odd trans polyalkenamers (CHCH(CH 2 ) 2 n +1 crystallize in orthorhombic unit cells, the equatorial dimensions of which are very similar to those found for orthorhombic polyethylene. The space group is the same (P nam ) for odd trans polyalkenamers or for orthorhombic polyethylene and the packing of the macromolecules is nearly identical for all these polymers. A three dimensional least squares refinement was carried out for trans polypentenamer and for trans polyheptenamer. The “full matrix” methods and the weighing scheme by Cruickshank were employed. An overall temperature factor was used in the refinement. The standard deviations of the final atomic co-ordinates of the C atoms range between 0·01 and 0·02 A for both polymers. The even trans polyalkenamers (CHCH(CH 2 ) 2 n ) p can crystallize either in a monoclinic unit cell or in a triclinic unit cell. The α and b axes of the monoclinic unit cells have the same value for all the trans polyalkenamers examined; the same is verified also for the triclinic unit cells. A three dimensional least squares refinement was carried out for the monoclinic forms of trans polydecenamer and of trans polydodecenamer. The standard deviations of the final atomic co-ordinates of the C atoms range between 0·02 and 0·03 A for both polymers. The triclinic form of even trans polyalkenamers may be in some way connected to the triclinic form shown by cold-worked polyethylene. The triclinic structure of trans polyoctenamer and of trans polydecenamer have been checked by a three-dimensional Fourier analysis. The standard deviations of the atomic co-ordinates range from 0·02 to 0·04 A for the C atoms of both polymers.

Crystalline Synthetic High Polymers with a Sterically Regular Structure.

Publisher Summary The discovery of stereospecific polymerization processes leading to new linear high polymers of vinylic and diolefinic hydrocarbons having a regular structure, also with regard to the steric configuration of the monomeric units, probably represents the most important event in the pure and applied macromolecular chemistry. In the field of linear macromolecules, some crystalline natural products such as cellulose and silk show sterically regular structures as they contain asymmetric carbon atoms. However, only one of the two possible enantiomorphous forms is present. Thus, the steric structure regularity of those polymers is because of a regularity already existing in the monomers that contain asymmetric carbon atoms. The monomers of those natural products exhibit optical activity; in fact, they rotate the plane of the polarized light. Therefore, the steric regularity of the corresponding polymers is not determined by the polymerization process that does not modify the steric structure of the monomeric units.

Polymerization of propylene with titanium trichloride and alkyl-alkoxy-aluminium chlorides

Abstract A description is given of the polymerization of propylene in the presence of catalysts prepared from titanium trichloride and alkyl-alkoxy-aluminium chlorides. These catalyst systems are very active in the propylene polymerization only in the presence of aluminium chloride, which may be present as a solid solution in TiCl3. Al(C2H5)2Cl was isolated from the mixture of reaction products of AlCl3 and C2H5Al(Cl)OC2H5. The results lead to the conclusion that the polymerization-active organometallic compound of aluminium is probably aluminium diethylchloride.

A new thermally stable copolymer of formaldehyde

Abstract By polymerizing anhydrous formaldehyde and dimethylketene in the presence of anionic catalysts (e.g. P(C6H5)3), it is possible to obtain a copolymer having prevailingly a polyoxymethylenic structure, containing ester units of the type. These units have a considerable effect on the thermal stability of the polymer since they hinder the complete unzipping of the polyacetalic chains. The chemical behaviour and the physical-mechanical properties of a copolymer having a content of 4 per cent by weight of dimethylketene, are compared with those of the acetylated homopolymer and of the trioxane—dioxolane copolymer.