Highly improved crystallization behavior of poly(L‐lactide) induced by a novel nucleating agent: substituted‐aryl phosphate salts

In this work, a novel nucleating agent (NA) based on substituted‐aryl phosphate salts was introduced into poly(L‐Lactide) (PLLA). The nonisothermal and isothermal crystallization behaviors of nucleated PLLA samples were investigated through differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and polarized optical microscope (POM). Furthermore, the effect of annealing treatment on the cold crystallization behaviors of nucleated samples was also investigated. The results show that the crystallization of PLLA, whether for the melt crystallization (including nonisothermal and isothermal crystallization process) or for the cold crystallization (including the cold crystallization occurring during the DSC heating process and during the annealing process), is greatly dependent upon the content of NA. At relatively lower NA content (≤0.1 wt%), the nucleation effect of NA is inconspicuous, however, at higher NA content (≥0.2 wt%), it exhibits great nucleation effect for the crystallization of PLLA. Further results show that the double endothermic peak of PLLA depends on the temperature applied for the crystallization. Copyright © 2012 John Wiley & Sons, Ltd.     

Detection of Chemical Warfare Nerve Agents via a Beckmann Fragmentation of Aldoxime

Abstract

A new (E)-pyrene-1-carbaldehyde O-tert-butyldimethylsilyl oxime 3 was synthesized for the detection of chemical warfare nerve agents, O-isopropyl methylphosphonofluoridate (GB) and O-pinacolyl methylphosphonofluoridate (GD). ¹H NMR spectrum showed that the tert-butyldimethylsilyl (TBDMS) group was deprotected using TBAF and the oximate supernucleophile was made. Upon addition of chemical warfare agents (GB and GD) (50 mol%), the reaction was completely finished within 5 min and also the color change of reaction mixture was observed under a hand-held UV lamp with the naked eye.     

Preparation of polyaniline grafted multiwalled carbon nanotubes and conductive application in polyetherimide

A methodology for improving antistatic property of polyetherimide (PEI) composite using polyaniline (PANI) grafted multi‐walled carbon nanotubes (MWNTs) as conductive medium was proposed. First, the MWNTs grafted with PANI (PANI‐g‐MWNTs) were prepared by in‐situ polymerization in an emulsion system. Subsequently, PANI‐g‐MWNTs were blended with PEI using N‐methyl‐2‐pyrrolidone as solvent. After removing the solvent, the PEI/PANI‐g‐MWNT composite was prepared. As assisted conductive medium, the grafted PANI molecular chains on MWNT surface were dispersed in the PEI matrix to decrease the percolation value of the antistatic composites. The structure and morphology of PANI‐g‐MWNTs were characterized by Fourier transform infrared spectroscopy, transmission electron microscope, thermogravimetric analysis, and X‐ray powder diffraction, respectively. The dispersion of PANI‐g‐MWNTs in PEI matrix was studied by scanning electron microscope. The electrical performance was characterized by highly resistant meter. The volume resistivity of the conductivity percolation threshold was 1.781 × 10^?8 S/cm when the loading of PANI‐g‐MWNTs was 1.0 wt%. The conductivity of PANI‐g‐MWNTs/PEI composites was found to be higher than that of pristine MWNTs/PEI composite. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanical and anti‐stabbing properties of modified thermoplastic polymers impregnated multiaxial p‐aramid fabrics

New forms of hybrid multiaxial nanocomposites with enhanced mechanical and stab resisting properties are presented. This study is motivated by the lack of knowledge in the study of the multiaxial fabric nanocomposites with two modified thermoplastic matrices for antiballistic protection. Introduction of 5 wt.% silica nanoparticles in the composite of polyurethane/p‐aramid/poly (vinyl butyral) leads to significant improvement in mechanical properties, and the addition of silane as a coupling agents and glutaraldehyde as a crosslinking agents yielded maximal values of storage modulus, tensile modulus and anti‐stabbing properties for hybrid nanocomposites. Ballistic resistance testing and penetration depth of the hybrid nanocomposites were visualized using image analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and Properties of pH-Responsive Polymers with Cadaverine Side Groups

A water-soluble monomer N¹-(4-vinylbenzyl)-pentane-1,5-diamine dihydrochloride (VBPDA) with cadaverine (1,5-pentanediamine) group was synthesized. pH-responsive polymer with cadaverine group was obtained by free radical polymerization of VBPDA using 4,4-azobis(4-cyanovaleric acid) (ACVA) as the initiator. The structure and molecular weight of the polymer were characterized by FTIR, ¹H-NMR and GPC-MALLS. Aggregation behavior of the polymer in aqueous solution was investigated by dynamic light scattering (DLS), UV-Vis and fluorescence measurements. The experimental results show that the fluorescence intensity of the aggregates decreases and the size of the aggregates increases with increasing pH due to the continuous dehydration of the cadaverine side groups.     

Further Studies on the Anionic Copolymerization of Styrene and Glycidyl Methacrylate in Toluene

Sequential anionic copolymerization of styrene and glycidyl methacrylate (GMA) was performed with the protection of argon under normal pressure, where styrene, GMA, toluene, THF, n-butyllithium and a small amount of lithium chloride (LiCl) were used as first monomer, second monomer, solvent, polar reagent, initiator and additive, respectively. Polystyrene-b-poly(glycidyl methacrylate) diblock copolymers (PS-b-PGMA) with well-defined structure and narrow molecular weight distribution were prepared by the copolymerization reaction of poly(styryl)lithium with GMA under certain temperatures. The copolymers were characterized using gel permeation chromatography (GPC), ¹H-NMR, ¹³C-NMR, thin layer chromatography (TLC) and hydrochloric acid-dioxane argentimetric methods. The effects of additives, copolymerization temperature and THF dosage on the copolymerization were studied. No chain transfer reaction of anionic polymerization of styrene in toluene was observed. Slightly broader molecular weight distribution of PS-b-PGMA was observed with the increase the GMA repeat units. Using THF/toluene blend solvent could reduce the polydispersity index (M _w /M _n ) and dissolve the copolymer better than toluene alone. Lower temperature (< -40°C) and LiCl are required to prepare PS-b-PGMA with narrower molecular weight distribution.     

NMR studies of conformations and molecular recognition of pyridinio-appended and nicotinamide-appended β-cyclodextrin

Abstract

The conformations of pyridinio-appended β-cyclodextrin (CDP⁺) and nicotinamide-appended β-cyclodextrin (CDNA⁺) were studied by NMR spectroscopy. The orientations of the pyridine residue of CDP⁺ and the nicotinamide residue of CDNA⁺ were determined by using a combination of NMR spectroscopic techniques. NMR spectra indicate that the shapes of the cavities of CDP⁺ and CDNA⁺ were changed after forming complexes. This change depended on the shape of the guest. CDNA⁺ could separate the ¹H resonances at the Cβ position of racemic tryptophan into two sets of resonances for each enantiomer.     

Study on the Supramolecular System of TAPP and Cyclodextrins by Spectroscopy

The ability of β-cyclodextrin (β-CD), γ-CD, hydroxypropyl-β-CD (HP-β-CD), trimethyl-β-CD (TM-β-CD), sulfurbutylether-β-CD (SBE-β-CD) and carboxymethyl-β-cyclodextrin (CM-β-CD) to break the aggregate of the meso-tetrakis(4-N-trimethylaminobenzyl)porphyrin (TAPP) and to form 2:1 inclusion complexes has been studied by absorption and fluorescence spectroscopy. The formation constants are calculated, respectively, by fluorimetry, from which the inclusion capacity of different CDs is compared and the inclusion mechanism of charged-β-CD (SBE-β-CD and CM-β-CD) is quite different from that of the parent β-CD. At lower pH, the complexation between TM-β-CD and H²TAPP²⁺ (the form of the diprotonated TAPP) hampers the continuous protonation of the pyrrole nitrogen of TAPP and the hydrophobic cavity may prefer to bind an apolar neutral porphyrin molecule. ¹HNMR data support the inclusion conformation of the porphyrin–cyclodextrin supramolecular system, indicating the interaction of the meso-phenyl groups of TAPP with the cavity of CDs. For this host–guest inclusion model, cyclodextrin being regarded as the protein component, which acts as a carrier enveloping the active site of heme prosthetic group within its hydrophobic environment, provides a protective sheath for the porphyrin, creating artificial analogues of heme-containing proteins. However, for TAPP, encapsulated within this saccharide-coated barrier, its photophysical and photochemical properties changed strongly.     

Hydrothermal synthesis and structural characterization of a one-dimensional coordination polymer [Zn(Pydc)(Dppz)] n (H2Pydc = 2,6-pyridinedicarboxylic acid, Dppz = dipyrido[3,2-a:2′,3′-c]phenazine)

A new metal-organic coordination polymer [Zn(Pydc)(Dppz)] _n (I) (H₂Pydc = 2,6-pyridinedicarboxylic acid, Dppz = dipyrido[3,2-a:2′,3′-c]phenazine) was hydrothermally synthesized and characterized by elemental analysis, IR and X-ray single-crystal diffraction. The X-ray diffraction analysis reveals that I crystallizes in the monoclinic system, space group P2₁/c. The Pydc^2? ligands adopt O,N,O′-tridentate chelating and monodentate bridging coordination mode to link two adjacent Zn2+ ions to form a one-dimensional (1D) zigzag chain. The adjacent chains are further linked through hydrogen bonds and π-π stacking interactions, forming a three-dimensional (3D) supramolecular framework. The unit cell parameters for I: a = 7.332(3) Å, b = 36.023(9) Å, c = 7.8838(13) Å, β = 105.65(3)^○, V = 2005.1(10) ų, Z = 4.     

Solvothermal synthesis and structural characterization of a new one-dimensional metal-organic framework [Co(Atibdc)(Dpa)] n (H2Tibdc = 5-amino-2,4,6-triiodoisophthalic acid, Dpa = 2,2′-dipyridylamine)

The title cobalt(II) coordination polymer, [Co(Atibdc)(Dpa)] _n (I) (H₂Atibdc = 5-amino-2,4,6-triiodoisophthalic acid, Dpa = 2,2′-dipyridylanine), has been synthesized under solvothermal conditions and characterized by elemental analysis, IR, and X-ray crystallography structural analysis. Complex I exhibits a one-dimensional chain structure in which 5-amino-2,4,6-triiodoisophthalate as a bridging ligand interconnects adjacent two Co(II) centers to form a helical chain structure. The asymmetric unit includes one Co(II) center, one atibdc ligand, and one Dpa ligand. Each Co(II) center is five-coordinated and surrounded by two nitrogen atoms and three oxygen atoms from one Dpa ligand and two individual Atibdc ligands, leading to distorted trigonal bipyramid geometry. Adjacent chains are further linked through hydrogen bonds, C-H-π and π-π stacking interactions to form a three-dimensional supramolecular framework.