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Crystallization is studied for poly(isoprene-1,4- cis) from Hevea brasiliensis (natural rubber [NR]) and from taraxacum kok-saghyz, mainly by collecting wide-angle X-ray diffraction patterns after processing and stretching. Although rubber samples before stretching are generally fully amorphous, crystallization can be induced in NR samples by processing at room temperature under moderate pressure. This phenomenon is possibly associated with nucleation by saturated fatty acid components. For rubber samples being fully amorphous in the undeformed state, strain-induced crystallization occurs only at high strain ratios (α > 4), leading to high degrees of crystalline phase orientation ( fc > 0.9 for α = 5). Rubber samples presenting some crystallinity already in the unstretched state, on the contrary, reach much lower degrees of axial orientation, even for high strain ratios ( fc < 0.7 for α = 5). These differences in crystallinity and in crystalline phase orientations produce large differences in stress-strain behavior of the rubber. By room temperature processing, the considered NR samples can also develop an unreported disordered crystalline modification, with low intensity of 120 and 121 reflections. This disordered crystalline modification, which is also maintained after axial stretching procedures, can rationalized by a structural disorder along the b axis, possibly associated with statistical sequences of A+TA− or A−T A+ conformations for poly(isoprene-1,4- cis) chains. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this contribution the preparation of composite syndiotactic polystyrene (s-PS) monolithic aerogels with nanofillers such as organically modified montmorillonite (OMMT) and graphene oxide (GO) is described. In these aerogels the crystallites that constitute the physical knots exhibit a nanoporous-crystalline form. The aerogels preparation procedure allows the inclusion of also large amount of nanofillers, without aggregation, at least up to a content of 20 wt.%. This allows to improve mechanical and electrical properties of the nanoporous-crystalline aerogels of s-PS, which are particularly suitable to remove selectively traces of pollutants from water and air. Composite aerogels exhibiting large nanofiller content, can be also used as masterbatches for polymer composites. [ABSTRACT FROM AUTHOR]

Graphene oxide efficiently promotes high regio- and enantioselective ring opening reactions of aromatic epoxides by indoles addition, in solvent- and metal-free conditions. The Friedel-Crafts products were obtained with enantioselectivity up to 99 % ee. The complete inversion of stereochemistry indicates the occurrence of SN2-type reaction, which assures high level of enantioselectivity. [ABSTRACT FROM AUTHOR]

Innovative nanocomposites are obtained by melt blending poly(1,4- cis-isoprene) (PI) and graphite oxide intercalation compounds (GOICs) with dimethyl di(hydrogenated tallow) ammonium (2HT) cations ionically bonded to the graphite oxide layers. GOIC samples with different contents of 2HT are prepared and homogeneously dispersed in the PI matrix. The X-ray diffraction pattern of the GOIC shows an intense 100 reflection due to the hexagonal rotator order of the methylene sequences of long alkyl chains. Said rotator order is present in the nanocomposites, in the absence of any evidence of stacked layers, suggesting the prevailing exfoliation of the GOICs. The cross-linking reaction promoted by sulfur is remarkably accelerated by the GOICs and the maximum modulus is enhanced. GOICs increase stresses at given elongations and the reinforcement under strain. [ABSTRACT FROM AUTHOR]

Fully biodegradable composites based on a commercial PHBV/PBAT blend with varying concentrations of neat or silanized clay nanotubes were prepared by twin-screw extrusion and filmed by melt blowing process. Thermal analysis suggested the simultaneous occurrence for the PHBV phase of both homogeneous crystallization and heterogeneous nucleation promoted by the included fillers. These phenomena show effects of mutual entities depending on the quality of the filler-matrix interface and the applied cooling rate. On the contrary, for the PBAT phase, although the filler may alter kinetics and mechanisms of crystallizations, no effect is reported in terms of its degree of crystallinity. All these evidences have been supported by structural investigations. Moreover, X-ray diffraction analysis indicated that the process of film blowing enables the formation of more perfect crystals and, as expected, favors the orientation of the included nanotubes of clay. POLYM. COMPOS., 34:1460-1470, 2013. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

An abstract of the article "Regio- and Enantioselective Friedel-Crafts Reactions of Indoles to Epoxides Catalyzed by Graphene Oxide: A Green Approach" by M. R. Acocella and colleagues is presented.