Polypropylene/layered double hydroxide nanocomposites: Synergistic effect of designed filler modification and compatibilizing agent on the morphology,thermal, and mechanical properties

This work addresses the optimization of the morphology, thermal, and mechanical properties of polypropylene/layered double hydroxide (LDH) nanocomposites. For this, the nanofillers were modified by a calcination rehydration process using two surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate, respectively. The nanofillers were characterized at each step of the modification process by thermal gravimetry, X‐ray diffraction, and Infra red spectroscopy. Furthermore, the impact of anionic modifiers on the filler surface energy and on the interactions toward water was analyzed. Polypropylene (PP)/LDH nanocomposites were then prepared by a melt intercalation process and a high molar mass maleic anhydride functionalized polypropylene (PPgMA) was introduced as a compatibilizer. The dispersion of LDH in the PP matrix was characterized and the thermal and mechanical properties of the corresponding nanocomposites were determined and discussed as a function of the filler modification, of the nanocomposite morphology, and of the filler/matrix interfacial properties. The nanocomposites prepared from SDS modified LDH and PPgMA exhibited superior properties thanks to an optimized filler dispersion state and improved interfacial interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 782–794     

Ultrasound promoted Barbier reactions and Csp3–Csp2 Stille coupling for the synthesis of diarylmethanes and substituted benzophenones

Here we present the preparation of a variety of diarylmethanes obtained via ultrasound Stille coupling under palladium catalysis between some substituted aryl compounds and benzyltributyltin compounds generated through sonicated Barbier reaction in a very short time reaction and excellent yield. The study reported below compares different methods to optimize the synthesis of usually unstable benzyltin derivatives and is another contribution to the investigation of Csp³–Csp² coupling process involving benzyl–aryl reagents. Substituted carboxylated benzophenones were easily prepared in a very good yield by oxidation of some diarylmethanes.     

A Deeper Insight into the Postpolymerization Modification of Polypenta Fluorophenyl Methacrylates to Poly(N‐(2‐Hydroxypropyl) Methacrylamide)

This work provides a detailed insight into the synthesis of N‐(2‐hydroxypropyl)methacrylamide (HPMA) polymers employing the activated ester approach. In this approach, polypenta fluorophenyl methacrylate (PFPMA)‐activated ester polymers are synthesized by the reversible addition–fragmentation chain transfer (RAFT) polymerization and transferred into HPMA‐based systems by the use of 2‐hydroxypropylamine. To prove quantitative conversion in the absence of side reactions, special attention is devoted to investigate different reaction conditions by different analytical methods (¹H, ¹⁹F, inverse‐gated ¹³C NMR, and zeta potential measurements). Furthermore the influence of common solvent impurities, such as water, is investigated. Besides differences in polymer tacticity, the poly(N‐(2‐hydroxypropyl) methacrylamide) (PHPMA) synthesized under water‐free conditions display the same properties like the conventional synthesized control‐PHPMA. However, 3% water content in the dimethylsulfoxide are already sufficient to yield PHPMA polymers with a negative zeta potential of –15.8 mV indication the presence of carboxylic groups due to partial hydrolysis of the activated ester.

     

Rapid quality checking of polyethylene water/gas-pipelines: a model based on pyrolysis-gas chromatography/mass spectrometry and discriminant analysis

Eighty-five samples taken from polyethylene (PE) water/gas-ducts were pyrolyzed (from triplicate to 9-fold analyses) at 700 °C for 20 s in an N₂ atmosphere using a platinum coil pyrolyzer and a tube cooled in liquid nitrogen. The pyrolyzed products were identified and quantified by gas chromatography/mass spectrometry (GC/MS), and subjected to discriminant analysis. The samples included intact materials and sections fractured both in-field and following laboratory tests. Statistical data treatment allowed the samples to be subdivided into three groups. These groups were consistent with a pattern that fits well with sample rating after a modified stress-cracking test based on pipe resistance to increasing internal pressure. Such results can be explained through the relationship between pyrolysis (PY) fingerprint and polymer structure, which is in turn known to be related to the lifetime of the material. Compared with semi-empirical mechanical tests which are seldom used by water companies because of their lengthy duration, the PY and GC/MS approach is faster, simpler, cost effective, and provides molecular data on the original samples. The statistical models based on PY and GC/MS can be a valuable tool for water/gas companies that need to check the quality of PE pipes and predict their lifetime prior to purchase and installation, thus, helping companies set appropriate quality standards to reduce the occurrence of failures along operating pipelines.     

An Amphipathic Alpha‐Helix Guides Maturation of the Ribosomally‐Synthesized Lipolanthines

The recently discovered strongly anti‐Gram‐positive lipolanthines represent a new group of lipidated, ribosomally synthesized and post‐translationally modified peptides (RiPPs). They are bicyclic octapeptides with a central quaternary carbon atom (avionin), which is installed through the cooperative action of the class‐III lanthipeptide synthetase MicKC and the cysteine decarboxylase MicD. Genome mining efforts indicate a widespread distribution and unprecedented biosynthetic diversity of lipolanthine gene clusters, combining elements of RiPPs, polyketide and non‐ribosomal peptide biosynthesis. Utilizing NMR spectroscopy, we show that a (θxx)θxxθxxθ (θ=L, I, V, M or T) motif, which is conserved in the leader peptides of all class‐III and ‐IV lanthipeptides, forms an amphipathic α‐helix in MicA that destines the peptide substrate for enzymatic processing. Our results provide general rules of substrate recruitment and enzymatic regulation during lipolanthine maturation. These insights will facilitate future efforts to rationally design new lanthipeptide scaffolds with antibacterial potency.     

Linear polyurethanes derived from alditols and diisocyanates

A set of linear [m,n]‐type polyurethanes was synthesized by polycondensation in solution from hexamethylene diisocyanate and 4,4′‐methylene‐bis(phenyl isocyanate) with alditols. Threitol, arabinitol, and xylitol bearing the secondary hydroxy groups blocked as methyl ethers were used. Either regioregular or nonregioregular polymers (depending on the configuration of the alditol) were obtained in high yields and with number‐average molecular weights within the 20,000–30,000 range. All these polyurethanes were amorphous with T_g being highly dependent on the aliphatic or aromatic nature of the diisocyanate used, but scarcely depending on the chemical structure of the alditol moiety. They were found to be stable up to near 300 °C, decomposing at higher temperatures through a complex three‐stage mechanism. Polyurethanes obtained from threitol did not show significant enhancement of hydrolytic degradability as compared with polyurethanes obtained from 1,4‐butanediol. Conversely, polyurethane prepared from xylitol and hexamethylendiisocyanate was found to be almost fully hydrolyzed in 1 month when incubated in water either at 80 °C and pH 7.4 or at 37 °C and pH 10. It was concluded that the alditol size seems to be of prime importance in determining the hydrodegradability of these sugar containing polyurethanes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4109–4117, 2007     

Symmetric Soliton Configurations of Bosonic String Theories

We obtain a reduction of the symmetry holographic principle for symmetric configurations of Nambu–Goto–Polyakov string theories in a semi-Riemannian space. The argument reduces the search of string configurations with a certain degree of symmetry to that for elastic curves in a corresponding orbit space. These solutions are solitons which are holographically related to particles that evolve along elastic worldlines in the orbit space. We also exhibit examples and applications to obtain soliton string shapes with cylindrical, rotational, toroidal etc. symmetry. In most of the cases we can determine the whole moduli space of symmetric solitons.     

A new, simple, and mild azidolysis of vinylepoxides

A new, simple, and mild regio-and stereocontrolled azidolysis of vinylepoxides with TMSN₃/BF₃ system is reported. The method appears of general value and works very well particularly in the presence of electron-poor olefins, regardless of the size of substituents on the heterocyclic ring.     

Solid-phase microextraction coupled to gas chromatography with flame ionization detection for monitoring of organic solvents in working areas

A solid-phase microextraction (SPME) method was developed for air monitoring of organic solvents frequently used in chemical laboratories (namely pentane, dimethyl ether, acetone, acetonitrile, dichloromethane, hexane, ethylacetate, tetrahydrofurane, cyclohexane, benzene, and toluene). SPME sampling conditions and chromatographic separation were optimised. Linearity of response for each component of the mixture was tested. Standard solutions containing all the compounds, at three different concentrations, were analysed in triplicate and the relative standard deviations (RSDs) were calculated. The method was applied to the monitoring of indoor air in a research chemical laboratory. An SPME fibre was used as a sampling device inside the laboratory. Moreover an SPME fibre was used as a portable sampling device in order to determine the effective human exposure. Comparison of the portable and fixed sampling device showed differences in the amount of solvents associated with activities performed nearby.