The crystallization and melting behaviour of two sets of ethylene/1-butene copolymers have been analysed by DSC. The samples, with comonomer content in the range from 0 to 21.5 mol%, were obtained by industrial processes using both Mg/Ti-based catalyst systems. The composition dependences of melting and crystallization temperatures were found to be strictly affected by the catalyst type. Moreover, logarithmic plots of the melting and crystallization enthalpy as a function of the ethylene content (mol%) in the copolymers fitted linear relationships whose slopes have been related to the critical sequence length of crystallizable ethylene units, depending on the catalytic system. These results are compared with those reported in the literature for ethylene/1-butene copolymers synthesized by other catalysts and are accounted for by a different distribution of the comonomer units in the macromolecules of the two sets of samples. 相似文献
Water extraction of the sterically hindered phenolic antioxidant Irganox 1010 from three polypropylene based polymeric films has been studied in isothermal conditions at 40, 50 and 70 °C. The films made of isotactic polypropylene and two different heterophasic polypropylene/ethylene–propylene monomers copolymers (PP/EPM copolymers) were immersed in closed water baths under nitrogen atmosphere in order to minimise the oxidative process. The amounts of antioxidant that have left the films and are dissolved in the water bath have been monitored over time by HPLC analysis and faster extraction kinetics were observed from the polymers than from the homopolymer. No appreciable amounts of Irganox 1010 were found in the extraction water at any time, whereas its degradation by-products were found by LC/MS analysis in the extraction water.
The experimental extraction kinetics from the three polymers were compared with the theoretical curves based on the Fick's diffusion equations solved both for a semi-infinite (degradation reaction faster than extraction) and a finite system (no degradation reaction) and Irganox 1010 was demonstrated to be extracted by water from polypropylene based material faster than predictable only on the basis of the values of its coefficient of diffusion in the polymers and of partition between water and polymer. 相似文献
Summary: The effect of metal catalysts in promoting the formation of the comb copolymer between a very low density polyethylene (VLDPE) grafted with diethyl maleate and PET has been studied in this paper following a model study based on low molecular weight molecules resembling the local structure of the reactive groups in the reference macromolecules. Ti(OBu)4 was used as the catalyst and the reactions were carried out under the same conditions as in the case of the macromolecules species. The model mixtures have been analyzed by FT‐IR, 1H and 13C NMR spectroscopy, thermogravimetric analysis (TGA) and GC‐MS and evidence of the degradation of ester bonds, deactivation of hydroxyl terminals of PET and the possible crosslinking of functionalized polyolefin have been observed. The molecular model process agrees with results obtained for the macromolecular system blending PET and VLDPE grafted with diethyl maleate in a Brabender mixer in the presence of Ti(OBu)4, as evaluated by mixer torque values and selective extraction results. Therefore, the present model study allows us to both obtain information about reaction mechanism in the complex melt biphasic system and to suggest new strategies to optimize the process.
Boehmite nanoparticles covered with a polymer shell enhancing the organophilicity of the surface were prepared by physical adsorption of a polyelectrolyte atom transfer radical polymerization (ATRP) macroinitiator followed by graft-polymerization of methyl methacrylate or 2-hydroxyethyl methacrylate. The presence of polymer chains adsorbed/grafted on the Boehmite was confirmed by attenuated total reflection infrared (ATR-IR) spectroscopy and by thermo-gravimetric analysis (TGA), which showed a significant amount of polymer covering the particles. The methodology of polymerization and the kinetics suggested the possibility to modulate the amount, type and thickness of grafted polymer shell. These organic-inorganic hybrid materials were melt compounded in a Brabender mixer with isotactic polypropylene in the presence of functionalized polypropylene. The dispersion degree of Boehmite nanoparticles in the polypropylene matrix as well as their reinforcing effect were studied by morphology characterization [scanning electron microscopy (SEM) and X-ray diffraction (XRD)], whereas thermal and thermo-mechanical properties were assessed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). 相似文献
Copolymers of trans-4-hydroxystilbene with (—)menthyl acrylate exhibit upon irradiation transåcis isomerization of the side-chain stilbene chromophores analogously to trans-4-hydroxystilbene-2-methylpropanoate, chosen as low molecular weight model compound. U.v. measurements on polymer samples indicate a deviation from first-order kinetics. In the fluorescence spectra of all-trans polymer samples both excimer and monomer emissions are observed. On irradiation the excimeric component is quenched much faster than the monomeric one. Fluorescence polarization experiments indicate a higher conformational rigidity of the stilbene chromophore when inserted in polymeric systems. Comparison of chiroptical properties of both unirradiated and irradiated copolymers suggests that on irradiation a local conformational rearrangement of macromolecules takes place. 相似文献
In the present paper the efficiency of side-chain benzophenone chromophores containing polymers has been tested in the u.v. photoinitiated polymerization of acrylic monomers. Poly(4-acryloxybenzophenone) (poly(ABP)) and copolymers of acryloxybenzophenone (ABP) with (-)-menthyl acrylate (MtA), methyl acrylate (MA) and 1-acryloxy-2-ethoxyethane (AEE) exhibit much higher efficiency than that observed for the low molecular weight model compound 4-(2-methylpropionyloxy)benzophenone (IBP). The experimental findings indicate that the efficiency of the copolymer as photoinitiator depends markedly on the nature of benzophenone non-containing co-units and on the sequence length of ABP monomeric units. When poly(ABP) is used as photoinitiator in combination with a tertiary amine such as N,N-dimethylaniline (DMA) or poly[4-(N,N-dimethylamino)styrene] (poly(DMAS)), its efficiency is higher than that observed for the corresponding IBP/DMA and IBP/poly(DMAS) systems. Only in the case of the substantially alternating copolymer of ABP with DMAS is the efficiency of the macromolecular photoinitiator lower with respect to that of the mixture of the monomeric analogues (IBP + DMA). 相似文献
We present a systematic study of the NH3-SCR reactivity over a commercial V2O5–WO3/TiO2 catalyst in a wide range of temperatures and NO/NO2 feed ratios, which cover (and exceed) those of interest for industrial applications to the aftertreatment of exhaust gases from diesel vehicles. The experiments confirm that the best deNOx efficiency is achieved with a 1/1 NO/NO2 feed ratio. The main reactions prevailing at the different operating conditions have been identified, and an overall reaction scheme is herein proposed.
Particular attention has been paid to the role of ammonium nitrate, which forms rapidly at low temperatures and with excess NO2, determining a lower N2 selectivity of the deNOx process. Data are presented which show that the chemistry of the NO/NO2–NH3 reacting system can be fully interpreted according to a mechanism which involves: (i) dimerization/disproportion of NO2 and reaction with NH3 and water to give ammonium nitrite and ammonium nitrate; (ii) reduction of ammonium nitrate by NO to ammonium nitrite; (iii) decomposition of ammonium nitrite to nitrogen. Such a scheme explains the peculiar deNOx reactivity at low temperature in the presence of NO2, the optimal stoichiometry (NO/NO2 = 1/1), and the observed selectivities to all the major N-containing products (N2, NH4NO3, HNO3, N2O). It also provides the basis for the development of a mechanistic kinetic model of the NO/NO2–NH3 SCR reacting system. 相似文献
As part of a fundamental and applied work on the development of an unsteady mathematical model of the NH3-selective catalytic reduction (SCR) process for design and control of integrated after-treatment systems of heavy-duty engines, we present herein a transient kinetic analysis of the standard SCR NO + NH3 system which provides new insight in the catalytic kinetics and mechanism prevailing at low temperatures. Based on kinetic runs performed over a commercial powdered V2O5–WO3–TiO2 catalyst in the 175–450 °C T-range feeding NH3 and NO (1000 ppm) in the presence of H2O (1–10%, v/v) and O2 (2–6%, v/v), an original dual-site modified redox rate law is derived which effectively accounts for NH3 inhibition effects observed during transient reactive experiments at T < 250 °C. We also demonstrate that implementation of the novel modified redox kinetics into a fully predictive 1D + 1D model of SCR monolith reactors can significantly improve simulations of SCR transient runs at different scales, including engine test bench experiments over full-scale SCR honeycomb catalysts. 相似文献