The high-resolution solid-state 13C NMR characterization of highly syndiotactic polypropylene (sPP) was performed. Each carbon atom of the repeating unit shows at different temperatures several resonances, which were fully assigned to conformational sequences in different phases or different states of the same phase. The helix chain conformation was confirmed to be the only one present in the crystal structure. Fine details about the crystalline packing were obtained from the methyl signals and explained by the introduction of statistical disorder in the distribution of the chirality of the chains within the lattice. The average chemical shift of the mobile amorphous phase was determined at high temperature, giving for the first time an accurate measurement of the conformer distribution and supporting a model described by a considerable trans content in the amorphous phase. On the other hand, the conformations in the amorphous phase below the glass transition (at 203 K) were singly identified. A further phase interpreted as a rigid amorphous phase, showing different relaxation properties and temperature dependence, could be also detected. The as-polymerized polymer was shown to be rich in this phase, which lies probably at the interfaces, associated with a less regular crystallization.

Isothermal crystallizations from the melt of samples of syndiotactic polypropylene having different degrees of syndiotacticity have been performed. The thermal behavior and the structural features of the melt-crystallized samples have been analyzed by differential scanning calorimetry and X-ray diffraction. According to this analysis, less stereoregular samples, crystallized in disordered modifications of form I with defects implying local arrangements of the chains such as in form II, present recrystallization phenomena during heating. For most stereoregular samples relevant recrystallization phenomena are absent. Extrapolation to the equilibrium melting temperature of syndiotactic polypropylene was attempted by using the Hoffmann−Weeks method, taking into account the occurrence of recrystallization and superheating phenomena. A value of nearly 182 °C has been obtained for the equilibrium melting temperature of the fully syndiotactic polypropylene.

The structural characterization of syndiotactic copolymers of propene with 1-butene, prepared with a single-center metallocene-based catalyst, is reported. The copolymers are crystalline in a whole range of comonomer composition. The increase of a and b axes of the unit cell from the values of syndiotactic polypropylene to those of syndiotactic poly(1-butene), with increasing content of 1-butene, indicates that the comonomeric units, propene or 1-butene, are included in the unit cells of both homopolymers. As-prepared copolymers having small contents of 1-butene are crystallized in a structure similar to that of form I of syndiotactic polypropylene, although disorder in the alternation of right and left-handed helical chains along both axes of the unit cell and in the stacking of bc layers of chains piled along a (b/4 shifts disorder) is present. With increasing content of 1-butene, the amount of b/4 shifts disorder increases and disordered modifications having structures intermediate between the limit-ordered models of form I of syndiotactic polypropylene and form I of syndiotactic poly(1-butene) are obtained. Samples with a content of 1-butene higher than 70−80 mol % crystallize in a structure similar to that of form I of syndiotactic poly(1-butene) (as well as of form II of syndiotactic polypropylene).

The role of Lewis bases in MgCl2 supported catalysts for olefin polymerization is a subject of continuous interest and discussion in order to obtain more and more active and stereospecific catalysts and to explain their stereoregulating mechanism. Through molecular calculation and conformational analysis it was possible to identify chelating diethers that have the correct oxygen‐oxygen distance necessary to tightly coordinate with the Mg ions of the support, even in the presence of other strong Lewis acids, and unable to give secondary reactions with TiCl4, AlR3, Ti‐C and Ti‐H bonds. The use of these donors has allowed the synthesis of catalytic systems that are both highly active and stereospecific even in the absence of external donors. Kinetic data of propylene polymerization with these catalyst systems are reported. The importance of the distance between the donor atoms in bifunctional Lewis bases has been proved also in the case of new classes of internal donors. Molecular modelling studies have enabled us to formulate models of active sites, located on some corners of MgCl2 crystallites, whose chirality is induced by the presence of a donor molecule in their environment. These models could explain, at least in part, the exceptional increase of isotactic polymer productivity observed for stereospecific catalyst systems, containing only the internal donor, with respect to catalysts lacking the Lewis base and could account for the influence of the donor on the molecular properties of the obtained polymers.

Ethene/propene copolymerizations were performed with catalytic systems composed of a stereorigid racemic isospecific metallocene and polymethylalumoxane. A number of complexes were used as representatives of three different classes of metallocenes. r-Me2C(3-t-Bu-Cp)2ZrCl2, r-Me2C(3-t-Bu-Ind)2ZrCl2, r-EBDMIZrCl2, r-EBDMTHIZrCl2, and r-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 were chosen as sterically hindered complexes. The parent metallocenes, r-Me2C(Ind)2ZrCl2, r-EBIZrCl2, and r-Me2Si(Ind)2ZrCl2 were also employed as well as other compounds bearing different substituents on the indenyl ligands such as r-Me2C(3-Me3Si-Ind)2ZrCl2, r/m-Me2C(3-Me-Ind)2ZrCl2, and r-Me2Si(2-Me-Ind)2ZrCl2. The reactivity ratios of copolymerization (r E and r P) were determined and examined in the light of the metallocene structure. The complexes that were particularly demanding from the steric point of view were identified as suitable candidates for promoting copolymerizations with a high product of reactivity ratios, giving r E r P in a range from 1.7 to 3.0. The other two classes of metallocenes gave rise to r E r P clearly lower than 1. A more complex situation was observed as far as the reactivity ratios r E and r P are concerned. The enhancement of the steric hindrance brought about in most cases an increase of r E but not a substantial decrease of r P. In some cases, r E was found to remain almost unchanged and r P dramatically increased. A correlation between the reactivity ratios and the metallocene structure is attempted.

Chem. reduced graphite oxide with strongly improved shape anisotropy was prepd. by Staudenmaier oxidn. of high surface area graphite, followed by hydrazine monohydrate redn. Selection of the starting graphite was effected on the basis of the highest shape anisotropy of the crystallites. The overall oxidn.-​redn. procedure preserves the in-​plane order of graphite and dramatically increases the out-​of-​plane disorder, which becomes similar to that one of carbon black. In particular, the overall procedure led to aggregates of few piled structural layers (D⊥ ≈ 2 nm) with increased periodicity perpendicular to the layers (from 0.339 nm up to 0.362 nm) and with high shape (D‖/D⊥ ≈ 13) and strain (ε⊥/ε‖ ≈ 15) anisotropy

A nanoGraphite (nanoG) having a high surface area and a high shape anisotropy, defined as the ratio between the crystallite dimensions in a direction orthogonal and parallel to structural layers, was used to prepare nanocomposites based on poly(1,4-cis-isoprene) (IR), in the neat polymer matrix and in the presence of carbon black (CB). Tensile and dynamic-mechanical measurements showed that nanoG forms a filler network at a relatively low concentration in neat IR and a hybrid filler network at a lower nanoG concentration in the presence of CB. A synergistic effect between the two carbon allotropes was found: composites containing both fillers present initial modulus values much higher than those calculated through the simple addition of the initial moduli of the composites containing only CB or nanoG.

A biobased Janus molecule was used to prepare water solutions of nano-stacks made by few layer graphene.The Janus molecule was 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (serinol pyrrole, SP), a serinol derivative obtained through the neat reaction of 2-amino-1,3-propandiol with 2,5-hexanedione, with atom efficiency of about 85%. SP contains the pyrrole ring, suitable for the interaction with carbon allotropes and hydroxy groups, that can easily interact with polar surroundings. Adducts, with about 14% by mass of SP, were prepared by reacting SP with a high surface area nano-sized graphite (HSAG), with about 35 graphene layers stacked in crystalline domains. Green methods were adopted, such as ball milling (HSAG-SP-M) and heating. Infrared spectra revealed peaks due to both HSAG and SP and additional peaks that could be attributed to the adduct. Both thermal and mechanical reactions left substantially unaltered the order in the graphitic layers and the interlayer distance, as shown by X-ray diffraction patterns. The relative intensity of the G and D band in the Raman spectrum was not modified by the thermal reaction, whereas enhancement of the D peak was observed after ball milling. Stable water solutions of HSAG-SP-M were prepared in a concentration range from 0.1 to 1 mg mL À1 . Centrifugation allowed isolation of adducts with few stacked graphene layers, as revealed by high resolution transmission electron microscopy. An image of the adduct showed an organic layer tightly adhered to the carbon surface. SP appears a suitable molecule for the easy functionalization of carbon allotropes, such as nanostacks of graphene layers, without substantially affecting the bulk crystalline organization and promoting the separation of the aggregates into stacks containing a low/very low number of graphene layers.