Sergio Brückner

Polymorphism in isotactic polypropylene

Abstract The paper is intended to summarize the studies devoted to the elucidation of the different crystal structures and crystal morphologies and of the different conditions favouring one or the other of the polymorphs of isotactic polypropylene. This outline takes into account 103 contributions produced in the course of about thirty-five years and is completed with 22 figures.

Fast firing of tiles containing paper mill sludge, glass cullet and clay

The paper describes results obtained in the development of a previous research. We study here, in fast firing, the sintering behaviour and measure some properties of tiles containing a mixture of 60 wt% of paper mill sludge and 40 wt% of glass cullet. The behaviour of this material is compared to those displayed by materials obtained by the same mixture added with 10, 20 and 30 wt% of a natural red clay. In parallel, the same properties are measured also on a reference blend, which is presently used to produce commercial tiles. We show that powders containing 60 wt% of paper sludge and 40 wt% of glass cullet to which 30 wt% of clay is added give rise to materials that display a stable sintering process and have good hardness and strength and therefore could be used for the industrial production of tiles.

The Structure of α,ω-bis(4-cyanobiphenyl-4′-oxy)heptane

Abstract The crystal structure of α,ω-bis(4-cyanobiphenyl-4′-oxy)heptane has been determined from single crystal X-ray diffractometry. The structure is monoclinic, space group P21/n with four molecules per unit cell. The cell parameters are a = 33.737(4), b = 11.084(2), c = 7.106(1) A, β = 94.01(3)°. The flexible spacer is in the all trans-conformation and the long axes of the two mesogen units make an angle of 34° with each other. No indication of grouping between mesogen units belonging to different molecules is detected in the packing analysis.

Configurational characteristics and nematic order of semiflexible thermotropic polymers

The stability and the molecular order of nematic states of thermotropic polymers comprising rigid groups connected by flexible spacers are found to be dominated primarily by the characteristics (configurational partition function) of highly extended conformers, which are favoured for packing. Moreover, both the macroscopic consideration of the enthalpies and the entropies of isotropic–nematic transitions and the microscopic probe by deuterium n.m.r. of labelled chains lead to the conclusion that the highly extended conformers are selected preferentially in polymeric nematogens. A number of unique results exhibited by polymer liquid crystals, i.e. strong effects of even–odd character of polymethylene spacers, abnormalities associated with —C(O)O— links [compared with —O— and —OC(O)— links] between rigid (phenylene) groups and polymethylenes and drastic differences between polymethylene and polyoxyethylene spacers, can all be attributed quantitatively to this conformational ordering, which is the most prominent feature distinguishing polymer liquid crystals from their monomeric counterparts. The orientational order parameters of a nematic polymer measured from both D and H n.m.r. spectra of labelled chains are found to be quite high, ca. 0.8 throughout the nematic region. These findings on conformational order and orientational order of polymer liquid crystals are compared with theoretical predictions based on ideal lattice chains and worm-like chains.

The polymorphic behaviour and the crystal structure of one modification of poly(dimethylphosphazene)

Abstract Poly(dimethyl phosphazene) displays, upon crystallization, a polymorphic behaviour showing two crystalline modifications, form I with a chain periodicity of 4.9 A and a melting point of 146°C and form II with a chain periodicity of 5.85 A and a melting point of 76°C. Form I, the only crystalline modification that is observed upon melting and recrystallization, has been completely characterized from a structural point of view through the study of X-ray diffraction patterns from oriented fibres and powder samples. A final structural refinement was carried out with the Rietveld method. The unit cell is monoclinic, space group P 2 1 c and the cell parameters are a = 6.345(2), b = 13.805(4), c = 4.887(2) A , β = 110.45(3)°.

Relationships between solid-state structures of enantiomers and the corresponding racemic compounds in small ring derivatives. Comparison of crystal structures and solid-state properties of (R)-(–)- and racemic 1-chloro-2,2-diphenylaziridine. Solvent effect on the racemization of (R)-(–)-1-chloro-2,2-diphenylaziridine

The synthesis of highly optically pure N-chloro-2,2-diphenylaziridine, in a crystalline form and sufficiently stable at room temperature, has enabled the study and the comparison to be carried out of the solid-state properties (e.g., the m.p. phase diagram, the crystal and molecular structures, and the i.r. spectra) of the enantiomer and racemic species of this small ring derivative. The solvent effect on the racemization of the optically active N-chloro-2,2-diphenylaziridine is relatively small, and this is attributed to the low basicity of the nitrogen atom of the N-chloroaziridine ring.

X-Ray structure and stereochemical properties of (S,S)-(–)-2-methylsulphonyl-3-phenyloxaziridine and of (S,S)-(–)-2-methylsulphonyl-3-(2-chloro-5-nitrophenyl)oxaziridine

X-Ray analysis of crystalline, optically pure 2-methylsulphonyl-3-phenyloxaziridine (2a) and 2- methylsulphonyl-3-(2-chloro-5-nitrophenyl)oxaziridine (2b), obtained by asymmetric oxidation of the corresponding prochiral N-benzlidenemethylsulphonylimine (1a) and N-(2-chloro-5-nitrobenzylidene)methylsulphonylimine (1b) with (1S)-(+)-peroxycamphoric acid, (+)-PCA, followed by fractional crystallization of the crude products, shows that the absolute configuration at the chiral nitrogen and carbon atoms of the oxaziridine rings of both (–)-(2a) and (–)-(2b) derivatives is (S,S). C.d. spectra of (–)-(2a) and (–)-(2b) indicate that the chiroptical properties of these compounds can be correlated with the observed (S,S) configuration. On the other hand, asymmetric oxidations of prochiral sulphides and olefins, carried out with both (–)-(2a) and (–)-(2b) as chiral oxidizing reagents, indicate that the stereochemical properties of these oxaziridine derivatives are dependent on the substituted or unsubstituted structure of the phenyl group directly linked to the carbon atom of the three-membered ring.

X-Ray absolute configuration and circular dichroic properties of a chiral oxaziridine containing two phenyl chromophores in a trans configuration. Application of the circular dichroism exciton chirality method to the optical activity of (S,S)–(-)-3-phenyl-2-phenylsulphonyloxaziridine

Bijvoet X-ray diffraction analysis of crystalline, optically pure 3-phenyl-2-phenylsulphonyloxaziridine (–)-(2), obtained by asymmetric oxidation of the corresponding prochiral N-benzylidenephenyl-sulphonylimine (1) with (1S)-(+)-peroxycamphoric acid, followed by fractional crystallization of the crude reaction product, shows that the absolute configuration at the chiral nitrogen and carbon atoms of the oxaziridine ring is (2S,3S). Absolute configuration of (2) was also determined independently by application of the circular dichroism exciton chirality method.

Structural investigation of a hindered aromatic amine and its derivatives

Abstract X-ray diffraction structural analysis of N-phenylpiperidine having two isopropyl groups in the ortho (1) and a nitro group in the meta (2) positions, has allowed the confirmation of the findings from molecular mechanics calculations on the simple derivative N-(2,6-diisopropylphenyl)piperidine (1) not bearing the nitro group, that the amino function is heavily twisted about the ipso-CN bond. In addition, there are a number of surprising features like the quasi-planarity of the location of the nitrogen atom and the three carbons attached to it, and the flattened nature of the isopropyl group. The hydrochloride (3) of 1 exhibits a peculiar stoichiometry: a hydronium ion coordinates three chloride ions; two of them also establish polar interactions with two NH groups. A great flattening about the N atoms is observed even in this case. The picrate (4) of 1 has the structure of an ammonium salt. Observed CN bond lengths both for the amino and nitro groups, which are to be found in planar and twisted arrangements, raise basic questions about the accepted and simplified views and correlations of substituent-ring interactions.

Fast Firing of Glazed Tiles Containing Paper Mill Sludge and Glass Cullet

The present paper reports on the results of some experiments on the progress of a previous research and describes the production, in single fast firing, of tiles containing 30 wt% of a natural red clay and a mixture of 42 wt% of paper mill sludge and 28 wt% of glass cullet which were coated with a commercial “matt white” glaze. Fired materials were characterized as a function of the top temperature (1090 or 1140 °C) reached during the fast sintering process made in an industrial roller kiln. It is observed that tiles fired at 1090 °C display the best overall performances since the matt glaze well covers the substrate concurring to maintain in line with the official standard for production the mechanical and physical properties of the tiles.