Combined effects of clay modifications and compatibilizers on the formation and physical properties of melt‐mixed polypropylene/clay nanocomposites

The melt mixing technique was used to prepare various polypropylene (PP)‐based (nano)composites. Two commercial organoclays (denoted 20A and 30B) served as the fillers for the PP matrix, and two different maleated (so‐called) compatibilizers (denoted PP‐MA and SMA) were employed as the third component. The results from X‐ray diffraction (XRD) and transmission electron microscope (TEM) experiments revealed that 190 °C was an adequate temperature for preparing the nanocomposites. Nanocomposites were achieved only if specific pairs of organoclay and compatibilizer were simultaneously incorporated in the PP matrix. For example, PP/20A(5 wt %)/PP‐MA(10 wt %) and PP/30B(5 wt %)/SMA(5 wt %) composites exhibited nanoscaled dispersion of 20A or 30B in the PP matrix. Differential scanning calorimetry (DSC) results indicated that the organoclays served as nucleation agents for the PP matrix. Generally, their nucleation effectiveness increased with the addition of compatibilizers. The thermal stability enhancement of PP after adding 20A was confirmed with thermogravimetric analysis (TGA). The enhancement became more evident as a suitable compatibilizer was further added. However, for the 30B‐included composites, thermal stability enhancement was not evident. The dynamic mechanical properties (i.e., storage modulus and loss modulus) of PP increased as the nanocomposites were formed; the properties increment corresponded to the organoclay dispersion status in the matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4139–4150, 2004     

Controlled/living polymerization of 2‐(diethylamino)ethyl methacrylate and its block copolymer with tert‐butyl methacrylate by atom transfer radical polymerization

Polymerization of 2‐(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous atom transfer radical polymerization under various reaction conditions is described. The effects of the initiators and solvents were examined. With 1,1,4,7,10,10‐hexamethyl triethylenetetramine/copper(I) chloride/p‐toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, poly(DEAEMA) with a polydispersity index as low as 1.07 was synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well‐defined block copolymers of DEAEMA and tert‐butyl methacrylate (tBMA) were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either p(DEAEMA) or p(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well‐defined copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2688–2695, 2003     

One Alkenylphenol and Steroids from the Aquatic Plant Monochoria Vaginalis

Two new compounds have been isolated from the whole plant of Monochoria vaginalis and characterized as: (10Z)‐1‐(2,6‐dihydroxyphenyl)octadec‐10‐en‐1‐one ( 1 ) (20R, 24R)‐campest‐5‐ene‐3β, 4β‐diol ( 2 ) together with nine known ones. The structures of these compounds were elucidated on the basis of spectral data and chemical evidence.     

Preparation,thermal properties,and flame retardance of epoxy–silica hybrid resins

A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′‐diaminodiphenylmethane with the sol–gel reaction of a phosphorus‐containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with 3‐glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, ¹H and ³¹P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass‐transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003     

Effects of annealing treatment on the properties of MEH-PPV/titania hybrids prepared via in situ sol-gel reaction

A uniform poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV)/titania hybrid film was successfully prepared by an in situ sol-gel reaction of titanium isopropoxide (TIP) in the presence of MEH-PPV/2-chlorophenol solution. The annealing treatment increased the conversion of TIP to titania as determined from evidence of the formation of Ti-O-Ti bonds in the Fourier transform infrared (FTIR) spectrum. Scanning electronic microscope (SEM) photographs showed that the morphology and distribution of titania in the hybrid film were strongly related to the amount of water in the in situ sol-gel reaction. The thermal stability of MEH-PPV/titania hybrids was enhanced by the annealing treatment. Small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) analyses indicated that annealing treatment promoted the ordered aggregation of the MEH-PPV chains and crystallization of titania to a certain extent. The blue shift in Ultraviolet-visible (UV-vis) absorption of pure MEH-PPV after annealing was ascribed to the small extent of decomposition and coil conformation which occurred at high temperature. A more-obvious blue shift for the hybrids was observed, which resulted from irregular aggregation and coil conformation of the MEH-PPV chains induced by heterogeneous point, TIP (titania). The red shift in the photoluminescent (PL) emission for pure MEH-PPV resulted from a certain extent of ordered aggregation after annealing. However, only a slight red shift in the PL emission peak for the hybrids was found due to the hindrance of ordered aggregation of MEH-PPV chains in the presence of TIP (titania).     

Nucleophilic substitution by arenethiolates at the carbene carbon of pentacarbonyl(methoxymethylcarbene)-metal(o) complexes (metal = Cr,Mo, or W)

The phenylthiocarbene complexes, [(CO)₅MC(CH₃)(SPh)] (M = Cr, Mo, or W) have been prepared in good yield by the reaction of [(CO)₅MC(CH₃)(OCH₃)] (M = Cr, Mo, or W) with NaSPh in benzene/methanol in the presence of HCl. A series of para-substituted phenylthiocarbene complexes of tungsten. [(CO)₅WC(CH₃)SC₆H₄Y)], (Y = p-Br, p-F, p-H, p-CH₃, p-OCH₃ or p-OH) have also been prepared by the reaction of the appropriate arenethiolate ion with [(CO)₅WC(CH₃)(OCH₃)]. Poor nucleophiles such as p-nitrobenzenethiolate and pentafluorobenzenethiolate did not react with [(CO)₅WC(CH₃)(OCH₃) to form the corresponding phenylthiocarbene complex. A mechanism accounting for the formation of these phenylthiocarbene complexes is proposed. The complexes have been characterized by their infrared, electronic, mass, ¹H NMR, and ¹³C NMR spectra. These spectroscopic data have been used to establish the structure of these complexes in solution and indicate that the phenyl ring bonded to sulfur is probably not coplanar with the “carbene” plane.     

Self-assembly of dendrimers by slippage

[reaction: see text] A dendrimer with rotaxane-like characteristics has been assembled under thermodynamic control from complementary wedge-shaped precursors by slippage in CH(2)Cl(2). The driving force for the self-assembly process is the molecular recognition that exists as a result of [N(+)-H.O] and [C-H.O] hydrogen bonds between an NH(2)(+) center in one Fréchet-type benzyl ether wedge and a dibenzo[24]crown-8 unit that links the other two such wedges.