All issues / Volume 3 (2009) / Issue 8 (August)
This is an editorial article. It has no abstract.
Long chain semiaromatic polyamides were synthesized by the reactions of p-phenylenediacetic acid with long chain aliphatic diamines, and characterized by Fourier transform infrared spectroscopy (FTIR) and by proton nuclear magnetic resonance (1H NMR). The thermal behaviors were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The solubility, dynamic mechanical, physical and mechanical properties of the polyamides were also investigated. The resultant polyamides have intrinsic viscosity ranging from 1.8 to 2.1 dl•g–1, their melting temperatures range from 254 to 290°C, and their glass transition temperatures obtained from dynamic mechanical analysis are in the range 87–113°C. The physical and mechanical properties of long chain semiaromatic polyamides were compared with those the PA9T. The results show that the heat resistance and the mechanical properties of poly(decamethylene-pphenylenediacetamide) (PA10P) are near to those of PA9T, so PA10P is a promising heat resistant engineering plastic.
Kinetic peculiarities of polycyclotrimerization process of dicyanate ester of bisphenol A (DCBA) in the presence of multi-walled carbon nanotubes (MWCNTs) have been investigated using Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy technique. It has been found that even very small amounts of MWCNTs (0.01–0.1 wt%) catalyze the reaction of polycyclotrimerization of DCBA leading to formation of polycyanurate network (PCN)/MWCNTs nanocomposite. However, some decrease in final degree of conversion for nanocomposites compared to the neat PCN within the temperature/time schedule used was observed. The kinetic rate constants increased with addition of MWCNTs and energies of activation were found to be significantly decreased even at low contents of MWCNTs.
Fluorescent DNA probe based on fluorescence resonance energy transfer (FRET) was prepared by solid-phase organic synthesis when CdTe quantum dots (QDs) were as energy donors and Au nanoparticles (AuNPs) were as energy accepters. The poly(divinylbenzene) core/poly(4-vinylpyridine) shell microspheres, as solid-phase carriers, were prepared by seeds distillation-precipitation polymerization with 2,2′-azobisisobutyronitrile (AIBN) as initiator in neat acetonitrile. The CdTe QDs and AuNPs were self-assembled on the surface of core/shell microspheres, and then the linkage of CdTe QDs with oligonucleotides (CdTe-DNA) and AuNPs with complementary single-stranded DNA (Au-DNA) was on the solid-phase carriers instead of in aqueous solution. The hybridization of complementary double stranded DNA (dsDNA) bonded to the QDs and AuNPs (CdTe-dsDNA-Au) determined the FRET distance of CdTe QDs and AuNPs. Compared with the fluorescence of CdTe-DNA, the fluorescence of CdTe-dsDNA-Au conjugates (DNA probes) decreased extremely, which indicated that the FRET occurred between CdTe QDs and AuNPs. The probe system would have a certain degree recovery of fluorescence when the complementary single stranded DNA was introduced into this system, which showed that the distance between CdTe QDs and AuNPs was increased.
Radiation processed ethylene vinyl acetate-multiple walled carbon nanotube nano-composites: Effect of MWNT addition on the gel content and crosslinking density
K. A. Dubey, Y. K. Bhardwaj, C. V. Chaudhari, V. Kumar, N. K. Goel, S. Sabharwal
Vol. 3., No.8., Pages 492-500, 2009
Vol. 3., No.8., Pages 492-500, 2009
Different compositions of ethylene vinyl acetate (EVA)/multiple walled carbon nanotube (MWNT) nano-composites were prepared by melt mixing and subjected to different doses of gamma radiation. The efficiency of radiation vulcanization was analyzed by sol-gel analysis, Charlesby-Pinner parameter estimation and crosslinking density measurements. Gamma radiation induced crosslinking was found to increase with MWNT fraction in EVA-MWNT nano-composites (p0/q0 in the range: 1.15–0.98). These results ruled out the possibility of a significant neutralization of single ionization spurs by MWNT addition. The incorporation of MWNT also resulted in increased hardness and higher density of the nano-composite matrix. The efficiency of multifunctional acrylates as crosslinking aid in the radiation-induced vulcanization of EVA-MWNT nano-composites was also investigated. The results established lower efficiency of methacrylates than of acrylates in the radiation vulcanization process.
A novel trifunctional epoxy resin 4-(3, 3-dihydro-7-hydroxy-2, 4, 4-trimethyl-2H-1-benzopyran-2-yl)-1, 3-benzenediol glycidyl (shorted as TMBPBTH-EPOXY) was synthesized in our lab to improve thermal performance. Its curing behavior and performance were studied by using 4, 4′-diaminodiphenyl sulfone (DDS) as hardener with the mass ratio of 100:41 of TMBPBTH-EPOXY and DDS. The curing activation energy was investigated by differential scanning calorimetry (DSC) to be 64.0 kJ/mol estimated by Kissinger’s method and 68.7 kJ/mol estimated by Flynn-Wall-Ozawa method respectively. Thermogravimetric analyzer (TGA) was used to investigate the thermal decomposition of cured compounds. It was found that when curing temperature was lower than 180°C, the thermal decomposition temperature increased with the rise of curing temperature and curing time. On the other hand, when the curing temperature was higher than 180°C, the thermal decomposition temperature went down instead with the increase of curing time that might be the over-crosslinking of TMBPBTH-EPOXY and DDS hardener. The glass transition temperature (Tg) of cured TMBPBTH-EPOXY/DDS compound determined by dynamic mechanical thermal analysis (DMTA) is 290.1°C.
A series of new amphoteric dendrimers have been synthesized by attaching dimethylbenzylaminoethyl acrylate chloride (Bz80), sodium acrylic acid (SAA) and modified polyoxyethylene (MPEO) units to a third-generation poly(amidoamine) (PAMAM) dendrimer core via Michael addition reaction. The structure of the dendrimers was confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), carbon 13 nuclear magnetic resonance (13C NMR) spectroscopy and by elemental analysis. Thermal stability and intrinsic viscosity were investigated. The applicable experiment exhibited the amphoteric dendrimers have high flocculation efficiency, which could be significantly improved by combining amphoteric dendrimers with polyacrylamide (PAM). The suitable mass ratio of the dendrimers and PAM was 2:3. The study would promote the use of amphoteric dendrimers as a flocculant in treating wastewater and as a new paper retention aid in papermaking.
Nanocomposite hydrogels based on poly(vinyl alcohol) – PVA and sepiolite have been prepared and their potential for drug delivery systems has been assessed by taking rifampicin as model drug. The nanocomposite hydrogels were characterized by WAXS and DSC and the swelling behavior and structural stability were evaluated. The effect of the presence of rifampicin, sepiolite and simultaneous rifampicin-sepiolite on the structure and swelling of the hydrogels was investigated. The swelling data were analyzed in order to evaluate the diffusion mechanisms of water. The results indicate that both rifampicin and sepiolite cause important modifications on microstructure of the PVA matrix, leading to changes on swelling and diffusional behavior.
Combining the two basic techniques used for the preparation of single polymer composites (SPCs), hot compaction and film stacking, a polyamide 6 (PA 6) single polymer composite was manufactured. The starting materials were PA 6 high tenacity yarn (reinforcement) and PA 6 film prepared via melt quenching (matrix), both expected to be the two principal polymorphic modifications of PA 6 and thus differing in their melting temperatures. The prepared single polymer composite is characterized by a layered structure and shows superior mechanical properties due to the good wetting – tensile modulus is improved by 200% and the ultimate tensile strength – by 300–400% as compared to the isotropic matrix film. Improvement of the interfacial adhesion via transreactions promoted by Sb2O3 as a catalyst was also undertaken.