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In March 2003, school reform was definitively approved by the Italian Parliament. The aims of the reform are to create a school which works together with parents to promote the individual development of children. After eighth class, pupils have to choose whether to continue schooling at secondary school or vocational school, the latter being organised by regional authorities. Though no definitive curriculum has yet been developed, there are clear directives on two relevant subjects: information technology and English will be learned by all Italian pupils starting with the first primary class. The experience of Rodari School, a primary school studied during the Organization for Economic Cooperation and Development (OECD) case‐study research, gains particular importance in this scenario. School reform was introduced early at this school. Every morning all the children switch on the computers in their classrooms, which are connected to the Internet. The web site (www. formicaio.it) is only a small part of th...

A study has been made of the relationship between crystallization regimes and multiple peaks in the melting endotherms of isotactic polypropylene (iPP). Some samples of this polymer can show multiple melting peaks in differential scanning calorimetry (DSC) scans: this phenomenon has been studied and associated with a regime III of crystallization, giving rise to a phase which appears disordered from a crystallographic point of view. During melting, this phase recrystallizes, giving a more ordered phase which melts at a higher temperature. On the contrary, crystallization in regime II produces a crystalline phase which melts with a single endotherm. These phenomena have been studied by DSC, by optical microscopy in polarized light and by X-ray diffraction; the results are discussed in terms of the proposed interpretation.

The morphological changes of isotactic poly(propylene) cast films have been investigated during the smectic- α-monoclinic phase transition and the following melting. The small- and wide-angle X-ray scattering techniques allow to point out the different behaviour of a homopolymer sample and of two propylene-ethylene copolymer samples as a function of the presence and concentration of the ethylene comonomer. During the smectic - a-monoclinic phase transition the crystallinity increase appears to be directly connected to the lamellar thickening and/or to the formation of new lamellar stacks.

DSC investigations on isotactic polypropylene (it-PP) quenched from the melt and annealed over a range of temperatures are reported. The results confirm the existence of saturation levels of the ordered phase for different annealing temperatures, previously revealed by X-ray diffraction methods. Thermal, X-ray diffraction, and density data are correlated in terms of the extent of the ordered phase present in the it-PP. DSC-Messungen an abgeschreckten und bei verschiedenen Temperaturen getemperten Proben eines isotaktischen Polypropylens (it-PP) werden beschrieben. In ubereinstimmung mit fruheren Rontgenmessungen zeigen die Ergebnisse, das sich bei den verschiedenen Tempertemperaturen in Abhangigkeit von der Temperzeit ein konstanter Sattigungs-Ordnungszustand einstellt. Die Ergebnisse der thermischen, rontgenographischen und Dichte-Messungen werden bezuglich des Kristallinitatsgrades im it-PP miteinander verglichen.

A new crystalline modification of nylon 10, named α∗, was obtained by evaporating a solution of the polymer in formic acid. The XRD pattern analysis indicates a chain packing similar, in the c axis projection, to that of melt-crystallized α-nylon 6 but indicates a reflection impossible to be indexed on the basis of a monoclinic lattice. By examining the XRD pattern of an oriented sample of α ∗ - nylon 10 , it was found that the polymer crystallizes in the triclinic system. Calculation gave the following cell parameters: a = 9.80 A ; b = 5.12 A ; c = 27.54 A ; a = 54°; β = 90°; γ = 110° . The most reliable structural hypothesis corresponds to a sheet packing of antiparallel planar chains linked by hydrogen bonds. These sheets (parallel to the ac plane), are spaced at 3.74 A, nearly as in α-nylon 6, and progressively shift at a constant value (3.03 A) along the c axis direction; also the sheets of α-nylon 6 are displaced by a constant value (3.73 A) along the c direction, but alternately up and down.

Some structurally disordered models for poly(tetrafluoroethylene) were elaborated and the corresponding calculated X-ray diffraction patterns compared with experimental patterns. This and differential scanning calorimetry results suggest some differences between the virgin powder and a sintered polycrystalline plate of poly(tetrafluoroethylene). These differences may be related to the crystal phase transitions that occur in a range of temperatures close to room temperature.

From X-ray diffraction patterns of uniaxially oriented fibers, the structures of Nylon 8 and Nylon 10 were determined. They crystallize in the monoclinic system (pseudohexagonal), space group P21/b, with four monomeric units in the unit cell. The crystallographic parameters of Nylon 8 are: a=4,77; b=9,54; c=21,9 A; γ=120°, and those of Nylon 10: a=4,78; b=9,56; c=26,9 A; γ=120° (c fiber axis). Both structures show a γ-type molecular packing, characterized by a shortening of the fiber repeat distances and by a twisting of the amide groups. Therefore, pleated sheets of parallel chains joined by hydrogen bonds are formed and the direction of the chains in adjacent sheets is alternately “up and down”. These structures result very similar to those of Nylon 6 and Nylon 12 in γ-form, demonstrating once more that, in this series, by increasing the number of methylene groups, the usual crystal structure becomes the γ-form.

During studies of polymorphism of polyamides with an even number of carbon atoms, it was thought worthwhile to re-examine the crystal structure and molecular packing of the α-form of nylon 6 by more advanced instrumentation and computing facilities. X-ray diffraction measurements on mono-oriented fibres confirm that nylon 6 crystallizes in the monoclinic system, with crystallographic parameters: a = 9.71 A , b = 8.19 A , c = 17.40 A (fibre axis), γ = 115°, 8 monomeric units in the unit cell and space group P22. The crystal packing can be represented by parallel sheets of hydrogen-bonded antiparallel chains; the sheets are all oriented in the same sense and alternately displaced 3.73 A along the c axis. The hydrogen bond distance is 2.98 A. Although the structure was substantially similar to that previously found, some differences were observed; they are discussed on the basis of theoretical calculations.

The α, γ, γ* polymorphous forms and the physical mixtures of the α and γ-like forms of Nylon 6 were examined from room temperature up to the melting point by X-ray diffraction techniques. The α- and γ*-forms evinced a more evident structural change as a function of temperature than the γ-form. The study carried out on the polymorphous forms of Nylon 6 at temperatures higher than room temperature furnished new insights in comparison to usual annealing. The level of structural order and the specific aspects of the structure were found to be largely determinant for the equilibrium state in the polymorphous forms of Nylon 6 from room temperature up to the melting point.

The influence of different annealing treatments on the crystalline order of isotactic paracrystalline polypropylene is described. The result support an intramolecular transformation mechanism based on a rewinding of hellcal segments of different lengths having opposite senses of spiralization. Such a mechanism is in agreement with the annealing time dependence of a particular order parameter and is sensitive to the temperature and not to the annealing time once the saturation order value is reached. This saturation phenomenon occurs very quickly at the higher temperatures. Der Einflus verschiedener Temperbedingungen auf die kristalline Ordnung von isotaktischem, parakristallinem Polypropylen wird beschrieben. Die Ergebnisse unterstutzen die Annahme eines bestimmten innermolekularen Umformungsprozesses. Angenommen wird eine Umorganisation von helixformigen Segmenten von verschiedener Lange und entgegengesetztem Drehsinn. Solch ein Mechanismus ist in Ubereinstimmung mit der gemessenen Abhangigkeit eines bestimmten Ordnungsparameters von der Temperzeit. Dieser Parameter zeigt sich empfindlich gegenuber der Tempertemperatur und bleibt nach Erreichen eines Sattigungswertes konstant. Die Sattigung stellt sich bei hoheren Temperaturen schr schnell ein.

The crystal structure of nylon 12 was determined from the X-ray diffraction patterns of uniaxially oriented specimens. The unit cell is monoclinic (pseudo-hexagonal) with the following dimensions: a = 4,79 A, b = 31,9 A (fiber axis), c = 9,58 A, β = 120°. There are four monomeric units in the unit cell and the space group is P21/c. The structure presents a distortion of the amide group from the planar chain conformation and it is rather similar to γ-nylon 6. The hydrogen bond length is about 2,80 A and the molecular packing is characterized by alternate, “up and down”, highly disordered sheets of parallel chains, linked by hydrogen bonds. The agreement between observed and calculated intensities has been improved by introducing a statistical disorder. Die Kristallstruktur von Nylon-12 wurde mit Hilfe von Rontgenbeugungsdiagrammen uniaxial orientierter Praparate bestimmt. Die Elementarzelle besitzt eine monokline (pseudo-hexagonale) Symmetrie mit den Parametern a = 4,79 A, b = 31,9 A (Faserachse), c = 9,58 A, β = 120°. Die Zelle enthalt 4 monomere Einheiten; die Raumgruppe ist P21/c. Die Amidgruppen sind gegenuber der Ebene der planaren Zick-zack-Kette verdreht. Fur die Lange der Wasserstoffbindung ergibt sich ein Wert von etwa 2,80 A. Die Struktur scheint der γ-Form des Nylons-6 ahnlich zu sein. Parallel laufende Molekule sind durch Wasserstoffbrucken verbunden und bilden sog. Rostebenen; diese sind mit einem hohen Unordnungsgrad antiparallel angeordnet. Die Ubereinstimmung zwischen den beobachteten und den berechneten Intensitaten konnte durch die Annahme einer statistischen Unordnung verbessert werden.

Isotactic polypropylene in its various forms shows considerable small angle X-ray diffraction spectra. After an examination of the experimental data obtained at temperatures between room temperature and the melting point, an interpretation is reported of these phenomena; it is based on Hosemann's theory of paracrystal, with particular regard to the correlations between distribution statistics and small angle spectra.

The new polyamide nylon 18 was synthesized, mainly to investigate whether a rather large number of methylene groups in the monomeric unit might change the chain packing in comparison with that of lower even nylons. By X-ray diffraction measurements on a mono-oriented fibre, the following crystallographic parameters were found: a = 4.76 A ; b = 9.52 A ; c = 46.9 A (fibre axis); γ = 120°. A γ-type packing for the chains was found, similar to that shown by other polyamides of the series.

An accurate measurement of the X-ray powder diffraction pattern of α ∗ - nylon 10 revealed some features related to structural disorder, including also para-crystallinity. A structural model is described in which these phenomena arise mainly from the relative position of the nylon 10 sheets either in their spacing or from their relative shifts parallel to the chain backbone.

A mathematical procedure for the investigation of the lattice disorder by stacking faults in polycrystalline solids has been used in studying samples of MgCl2 activated by ball milling for various times in the presence of TiCl4. These samples have been investigated by X-ray diffraction and by measurements of surface area, crystallite dimensions, Ti content after washing and catalytic activity in the polymerization of ethylene. A good relationship has been confirmed between activation time and activity; furthermore, the structural variations introduced by ball milling are mainly associated with rotational disorder of the Cl-Mg-Cl triple layers. Nevertheless, the analysis by X-ray diffraction is not unequivocal about the relationships between structure and activity: other significant parameters, such as the surface area and the porosity, are probably very important.