Iranian polymer journal
Volume:20 Issue: 11, 2011

Nano-attapulgite (nano-AT) particles organically-modified with the silanecontaining epoxide groups were incorporated into a mixture of trimethylol-1,1,1- propane trimethacrylate, a tri-functional acrylate (TMPTMA) and methyl-hexahydrophthalicanhydride (MeHHPA)-cured CER was prepared for nanocomposites. The surface modification with silane of nano-AT was characterized by means of Fourier transform infrared spectroscopy (FTIR), and the results showed that the characteristicpeaks of silane, such as 2966, 2886, 1010, 804 and 750 cm-1 were observed in theFTIR spectra of nano-AT modified by silane, which indicated that silane coupling agenthad already been grafted successfully on the surface of AT nanoparticles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the microscopic structures of nanocomposites. The microscopy results displayed that a uniform dispersion of organically-modified nano-AT by silane in the polymeric matrix was obtained, which led to the improvement of the macroscopic properties of nanocomposites. The macroscopic properties of nanocomposites, suchas impact strength, storage modulus, tan δ, thermal stability and the dielectric properties were measured. It is found that within the range of 10 to 20 pbw the higher the nano-AT modified by silane concentrations the greater is impact strength of nanocomposites where at 30 pbw it reaches 11.2 kJ/m2 in contrast with 5.9 kJ/m2 of the CER/TMPTMA system. Dynamic mechanical analysis (DMA) results showd that a glass transition temperature (Tg) found in nanocomposites was assigned to the epoxy phase modified by TMPTMA. With increase in nano-AT modified by silane concentration there were gradual higher values in both Tg and the storage modulus of nanocomposites. Additionally, the results of thermogravimetric analysis (TGA) revealed that thermal stability of nanocomposites was apparently improved in comparison with the CER/TMPTMA system. Dielectric measurements showed that the resulting nanocomposites also displayed quite different dielectric behaviours compared with the CER/TMPTMA system.

The effects of electron beam (EB) irradiation on dielectric breakdown voltage(BDV) and insulation resistance (ρI) changes of poly(ethylene-co-tetrafluoroethylene)(ETFE) insulated electric wire were investigated. Electric wire was prepared by extruding pristine ETFE. The samples were irradiated in air at room temperature by a universal EB accelerator by doses ranging from 1 to 20 Mrad. The thermal behaviour of extruded samples has been also investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). When the ETFE insulated wire was exposed to EB irradiation, BDV and ρI were decreased gradually with irradiation dose. As the irradiation dose increased, the char formation and size of breakdown point were decreased significantly (above 10 Mrad). In TGA study, the thermal stability of EB- irradiated ETFE samples decreased significantly with radiation dose. For ETFE-20 the TGA traces showed a shift of the weight loss towards lower temperature with stabilization of 50°C lower than pristine ETFE. DSC Melting temperature (Tm) and crystallization temperature (Tc) of EB-irradiated ETFE tended to decrease as the irradiation dose increased. The crystallinity (χ) was slightly increased up to 5 Mrad irradiation dose and decreased significantly with irradiation dose above 5 Mrad. An increase in χ values occurred due to chain scission in the amorphous region, which led to crystallite perfection. The chain scission process created shorter polymer chain links which became easier to fit into a localized crystalline domain. At higher EB irradiation dose, the crystalline structure tended to be destroyed which led to decreases in Tm and Tc. After EB irradiation, the tensile properties and scrape abrasion resistance of ETFE were also decreased with respect to pristine ETFE.

The cationic polyelectrolyte of P(CMTC-DMC-AM) was synthesized by dispersionpolymerization in aqueous solution of ammonium chloride, using acrylamide(AM) and dimethylaminoethyl methacrylate methyl chloride (DMC) as main rawmaterials, N-carboxymethylthioureidochitosan (CMTC) as both one of reactants andthe stabilizer, 2,2'-azobis(2-amidinopropane) dihydrochloride (V-50) as the initiator. Theeffects of the major reaction variables, such as the mass proportion of CMTC and themonomers, the mass ratio between monomers and the total amount of the reactantswere investigated. In addition, the product was characterized by Fourier transforminfrared (FTIR) spectroscopy and proton nuclear magnetic resonance (1H NMR) spectroscopy. The results showed that CMTC had participated in the polymerization process with DMC and AM by the function of initiator under certain conditions. The product agglomerated when the mass proportion of CMTC, AM and DMC was less than0.67:6.0:6.0, while particles would be flocculated due to the flocculation action of CMTCwhen the proportion was up to 0.67:4.0:4.0. The molecular weight increased with theincrease of DMC, but the product agglomerated when the proportion of AM to DMC wasless than 3:8. The total concentration of CMTC, AM and DMC also influenced the polymerization enormously. At high concentrations, the dispersion was disturbed byagglomeration due to coalescence or cross-linking of the polymer chains. At lower concentration, the molecular weight greatly decreased, due to insufficient adsorption ofmonomers on the particles. The optimum reaction conditions for obtaining a stableaqueous dispersion were concentrations of 0.67 g, 5.5 g and 5.5 g per 100 mL de-ionizedwater for CMTC, AM and DMC, respectively, under the conditions of 32 g forammonium chloride and 0.0105 g for initiator and reaction temperature of 60°C for 5 h.

Bulky aryl α-diimine nickel(II) complexes with hydroxy functionality at the para-aryl position based on acenaphthenequinone with high efficiency were synthesized and characterized. These hydroxy functionalized ligands with different substitutes on their 2,6-ortho-aryl position including methyl, isopropyl, phenyl, 4-tbutyl- phenyl were used in ethylene polymerization. Ethylene polymerization was carried out using α-diimine nickel(II) complexes at different concentrations of ethyl aluminium sesquichloride (EASC) as an efficient cocatalyst. The effects of polymerization temperature from 10°C to 60°C and hydrogen concentration on catalysts performance were also investigated. The highest activity was achieved at 45°C and the activity was decreased at higher temperature for catalysts b and d the same as b'. The behaviours of these complexes were also compared with the same catalysts without hydroxy functionality. As expected, the α-diimine catalyst bis[N,N'-(4-(3-hydroxypropyl)- 2,6-di((4-t-butyl-phenyl)-phenyl))imino]acenaphthene nickel(II) dibromide (d) and bis[N,N'-2,6-di((4-t-butyl-phenyl)-phenyl)imino]acenaphthene (d') had higher yield and molecular weight because of higher steric blocking of metal axial sites which leads to higher insertion rate of monomer and retardation of chain transfer. These catalysts polymerized ethylene in 45°C and 10 bar monomer pressure with exceptional activity up to 30.1×106 g PE/mol Ni.h. In the case of 2,6-di-(4-t-butyl phenyl) aryl α-diimine nickel(II) catalysts, the molecular weight increased up to 3.9×106 g/mol with polydispersity index of 4.74. Despite the behaviour of Brookhart catalysts, this α-diimine catalyst d did not show any significant drop in its activity in presence of hydrogen which was added to polymerization reaction to control polymer molecular weight.

Natural fibres have received vast attention because of their combustible, non-toxic, low cost, hydrophilic and biodegradable properties. In this study, functionalization of cannabis indica fibre has been carried out by its grafting with acrylic acid (AAc) using a Ce3+-HNO3 redox initiator in an aqueous medium. Different reaction parameters such as reaction time, pH, reaction temperature, concentrations of initiator, monomer and nitric acid were optimized to achieve the maximum percentage of grafting (21.08%). The low graft yield obtained with acrylic acid was because of its high affinity towards water. A suitable mechanism to explain initiation, propagation and termination of graft copolymerization has also been proposed. The kinetics of the graft copolymerization of acrylic acid onto cannabis indica fibre has also been studied. It has been found that the rate expression for graft polymerization is (Rg) = k[I]0.63[AAc]1.22. The overall activation energy for the graft copolymerization of AAc onto cannabis indica fibre was found to be 15.25 kJ/mol within the temperature range of 25-45°C. Besides kinetic study the grafted samples were also evaluated for their physicochemical properties such as swelling behaviour in different polar and non-polar solvents along with resistance towards acid and base. Graft copolymerized samples have been found to show less resistance towards chemicals as compared to the raw fibre. Furthermore, the grafted samples were characterized by different techniques such as Fourier transform infrared (FTIR), scanning electron microscope (SEM), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) studies. Thermal stability of the fibre has been found to decrease after graft copolymerization which is also supported by activation energy (Ea) values calculated both for raw and grafted fibres.

Awell-defined poly(n-butyl acrylate) (PBA) homopolymer was prepared by activatorsgenerated by electron transfer (AGET) ATRP at 90°C in N,N-dimethylformamideusing ferric chloride hexahydrate (FeCl3.6H2O)/succinic acid (SA) as a catalyst and ethyl 2-bromoisobutyrate as an initiator. Ascorbic acid was selected as a reducing agent. The kinetic results showed that a linear increase of molecular weights of polymers with monomer conversion and a relatively narrow polydispersity (<1.25), when the conversion is beyond 40%, is an indication of a polymerization controlled by AGET ATRP of n-butyl acrylate (nBA). That is to say, (FeCl3.6H2O)/SA catalyst complex is demonstrated to be highly efficient for the AGET ATRP of nBA. The effects of different molar ratios of [FeCl3.6H2O]/[SA] and the concentration of ascorbic acid on polymerization rate were investigated. The maximum polymerization rate was obtained at molar ratio of [FeCl3.6H2O]/[SA] = 1:2 and gave the best control of molecular weight and the distribution of polymer molecular weight. The polymerization reaction rate decreased when the higher or lower molar ratio of [FeCl3.6H2O]/[SA] was employed.The polymerization rate increased with higher content of ascorbic acid. The effects ofdifferent solvents on the polymerization were investigated. The experimental resultsshowed that the polymerization rate was faster in polar solvent (such as DMF) than thatin non-polar solvent (such as benzene). The obtained polymers had higher molecularweights with narrow distribution of molecular weight in DMF than that in benzene.Moreover, the obtained PBA was used as a macroinitiator in the chain extension experiment via AGET ATRP. The molecular weight of polymer increased after chain extension experiment. The chain extension experiment confirmed the living character of the polymerization system. The resultant PBA was characterized by 1H NMR, FTIR and gelpermeation chromatography.