Small amounts of carbon nanofillers, specifically high-surface-area graphite (HSAG) and more effectively carbon black (CB), are able to solve the well-known problem of degradation (molecular weight reduction) during melt processing, for the most relevant biodegradable polymer, namely poly(lactic acid), PLA. This behavior is shown by rheological measurements (melt viscosity during extrusion experiments and time sweep-complex viscosity) combined with gel permeation chromatography (GPC) experiments. PLA's molecular weight, which is heavily reduced during melt extrusion of the neat polymer, can remain essentially unaltered by simple compounding with only 0.1 wt % of CB. At temperatures close to polymer melting by compounding with graphitic fillers, the observed stabilization of PLA melt could be rationalized by scavenging traces of water, which reduces hydrolysis of polyester bonds. Thermogravimetric analyses (TGA) indicate that the same carbon fillers, on the contrary, slightly destabilize PLA toward decomposition reactions, leading to the loss of volatile byproducts, which occur at temperatures higher than 300 • C, i.e., far from melt processing conditions.

The ring-opening reactions of epoxides with amines were efficiently and regioselectively catalyzed by high-surface-area graphite and graphene oxide under metal-free and solventfree conditions. For epoxides withouta ryl groups, catalytic activity waso bserved only for graphene oxide,a nd hence, the activity must have been due to its acidic groups. For styrene oxide, instead,g raphite and graphene oxide exhibited rather similar catalytic activities, and hence, the activity was mainly due to activation of the electrophilic epoxide by p-stacking interactions with the graphitic p system.T he described aminolysis procedure is green and cheap because the catalyst can be recovered and recycled without loss of efficiency.M oreover, these heterogeneous catalysts exert high stereoselective control in the presence of nonracemic epoxidesa nd provide chiral b-aminoa lcohols with enantiomeric excess values up to 99 %.Epoxider ing-opening reactions are useful methods to provide multifunctionalc ompounds ready to be used as versatile intermediates in total synthesis or as precursors of relevant molecules. As three-membered heterocyclic rings,e poxides are more reactive than ethers owing to ring strain anda re susceptible to attack by ar ange of nucleophiles, including nitrogen (e.g.,a mmonia,a mines, and azides), oxygen (e.g.,w ater,a lcohols, phenols, and acids),a nd sulfur (e.g.,t hiols) containing compounds, and this leads to bifunctional molecules of great industrial value.In particular, epoxy ring-opening reactions with amines are well documented, and with the choice of specific physical parameters (e.g.,h eating, [1,2] microwave, [3][4][5] and ultrasound [5] ), the use of polar reaction media (e.g.,i onic liquids, [6] fluoro alcohols, [7] or water under differentp Hc onditions [8,9] ), or the use of catalysts or activators as homogeneousc atalysts (e.g., Brønsteda cids and bases [6,[9][10][11][12][13][14] ands everalm etal salts and/or complexes [15][16][17][18][19][20][21][22][23][24][25][26][27][28] ), good results have been achieved, although most suffer from poor regioselectivity,h igh temperature, and/ or stoichiometrica mountso ft he catalysta nd the use of excess amounts of reagents.The use of heterogeneous catalyst as solids (e.g.,silica gel, [29] nanosilica, [30] functionalized mesoporouss ilica, [31][32][33] alumina and/or modifieda lumina, [34][35][36][37] nanoaluminos ilicates, [38][39][40][41][42] montmorillonite-K10 clay, [43] sulfated zirconia, [44,45] annotitanium dioxides, [46] heteropolya cids, [47] polyoxometalatei norganic metal oxygen clusters, [48] Amberlyst-15, [49] nanocrystalline zircosilicate, [50] and iron oxides [51] )h as tried to meet the need for more sustainable protocols that assure good regioselective control,o ften lost to competitive polymerization/isomerization of the epoxides.However,ametal-free, highly regioselective procedure is still missing. One of the emerging promises in sustainable chemistry is carbon-based materials, whicha re already used in some important synthetic reactions ...

A simple and eco-friendly procedure of esterification of graphite oxide (GO), which uses acetic anhydride as a model reagent and ethyl acetate as a green solvent, is reported. The procedure leads to high functionalization degrees (at least up to 4.5 mol % of acetyl groups, referred to as graphitic C atoms) and it is much more effective than the literature method based on pure acetic anhydride. Surprisingly, our acetylation procedure does not destroy or reduce GO crystallinity but, irrespective of a substantial increase of distance between GO layers (from 0.84 nm up to 0.95 nm), leads to an increased order in the direction perpendicular to the graphitic planes. This phenomenon indicates that acetyl groups of acetylated GO (AcGO) are easily accommodated between graphitic layers, even improving interlayer order. The esterification procedure is generally applicable with various anhydrides providing differently functionalized graphite oxide. Dispersion of crystalline functionalized GO in volatile organic solvents followed by solvent fast removal, can easily lead to complete exfoliation.

Half-titanocene (CpCH2CH2OCH3)­TiCl3 (1), (Cp = cyclopentadienyl), activated by methylaluminoxane (MAO), has been tested in the polymerization of styrene in a suitable range of temperatures, obtaining a new material consisting of syndiotactic–atactic stereoblocks of polystyrene. The monoanionic bidentate ancillary ligand of the titanium based catalyst, consisting of a cyclopentadienyl bearing an alkyl ether, is a hapto-flexible ligand because the ether group can either be coordinated or not to the metal, depending on reaction temperature. Thus, the ether group can give rise to two possible catalytic sites: (i) syndiospecific, when the ether group is not coordinated to the metal center, and (ii) aspecific, when it is coordinated to titanium. Consequently, it produces polymer chains having syndiotactic and atactic stereoblocks. In fact, in the range of temperature considered (0–19 °C), syndiotactic polystyrene was produced at 19 °C, atactic polystyrene at 0 and 5 °C, and syndiotactic–atactic stereoblock polystyrene at 10 and 15 °C.

No abstract