Iranian polymer journal
Volume:19 Issue: 8, 2010

Aseries of superabsorbent composites were synthesized through graft copolymerizationof acrylic acid (AA) onto carboxymethyl cellulose (CMC) in the presence of celite powder using N,N''-methylenebisacrylamide (MBA) as a cross-linking agent and ammonium persulphate (APS) as an initiator. The chemical structure and thermal properties of the composite hydrogels were characterized by FTIR spectroscopy and TGA methods, respectively. Morphology of the samples was examined by scanning electron microscopy (SEM). In free-state, the swelling conditions and hence the related data are not real, because in all their applications the swelling particles of superabsorbent must absorb aqueous solutions while they are under pressure. Therefore, the effect of the reaction variables (such as monomer and cross-linker concentrations and CMC/celite weight ratio) on the saline-absorbency under load (AUL) application was investigated. The AUL values were estimated using a simple AUL tester at two different pressures (0.3 and 0.9 psi). Surprisingly, the new synthesized composite samples exhibited about 86 g/g absorbency in 0.9% NaCl solution under 0.3 psi pressure. The AUL values considerably decreased withincreasing the MBA concentration, 53.4 g/g (CMC/celite = 0.5/1.5 and P = 0.3 psi) vs.42.4 g/g (CMC/celite = 0.5/1.5 and P = 0.3 psi). The ionic monomers increased saline-absorbency under load significantly and the effects of parameters such as monomer and cross-linker concentrations, and CMC/celite weight ratio were not considerably different from the free swelling. Therefore, this new synthesized composite may be considered as an excellent candidate for various industrial applications.

Modified Flory-Huggins theory with concentration dependent binary interaction parameters is often used to predict the phase diagram in a ternary nonsolvent/ solvent/polymer system. The interaction parameters in this model are usually determined experimentally which limit the model predictive capability. In this paper a compressible regular solution (CRS) model was used to predict the phase diagram of a membrane forming water/tetrahydrofuran/poly(vinyl chloride) system, by pure component properties such as, solubility parameter, coefficient of thermal expansion and hard-core volume. In this respect, the binodal curve, spinodal curve and the critical point were determined by numerical calculations. Properties of components that were needed for these calculations have been taken from available data in the literature. Experimental cloud point data were obtained by the titration method of PVC in THF solutions with concentrations reaching 15 wt%. The good agreement between the theoretical binodal and experimental cloud points indicates that this model is a promising method to calculate the theoretical phase diagram for membrane forming systems, with particular attention to the fact that no adjustable parameters such as binary interaction parameters should be used for theoretical calculations. The result of these calculations revealed that small amounts of water (less than 10%) is needed for liquid-liquid phase separation in ater/tetrahydrofuran/poly(vinyl chloride) system

The branching copolymerization of styrene (St) and methyl methacrylate (MMA) with divinylbenzene (DVB) as branching agent was conducted using atom transfer radical polymerization (ATRP). The kinetics and extent of branching with respect to monomer convesion were studied in details. Gas chromatography (GC), proton nuclear magnetic resonance (1H NMR) spectroscopy and dual detection size exclusion chromatography (DD-SEC) were used to monitor the reactions and analyze the resulting copolymers. The analysis of reactants conversion revealed that the conversion rate of DVB, having two double bonds, is only slightly faster than those of the monomers, with no donor/acceptor interactions between DVB molecules and the monomers. The molecular weight increases slowly which is still somehow larger than the theoretical value in the early stages; then deviates significantly from the its theoretical estimation beyond 40% conversion and increases steeply at later stages of 70% monomer conversion. These results suggest that branching takes place in the early stages of the reaction regardless of any possible donor/acceptor interactions between the monomers and DVB molecules, and the coupling reaction originates mainly from the primary chain resulting in small chain branching. Coupling reaction between the branched chains becomes significant in the later stages of the copolymerization which produces highly branched chains. The reaction system contains three components throughout the reaction: the primary chains, the slightly branched chains comprising of two primary chains, and the highly branched chainsconsisting of 3 or more primary chains. Although the weight fraction of the branchedchains increases with monomer conversion, there is finally 20% primary chains stillleft in the reaction system which gives rise to limited molecular weight and highpolydispersity of the branched polymers prepared through ATRP using divinyl monomeras the branching agent.

Effects of initiator and surfactant concentrations and temperature on styrene conversion and polymer particle size distribution (PSD) in a batch emulsion polymerization are investigated through simulation and experimental studies. The detailed model based on population balance (zero-one model), accounting for nucleation, growth and coagulation phenomena has been used for prediction of particle size distribution. In checking the effect of initiator concentration on final PSD, it was noticed that when critical micelle concentration (CMC) is kept constant, the model cannot predict PSD very well. Thus, a correlation for calculating critical micelle concentration has been proposed and incorporated in modelling to justify the effect of initiator concentration on final PSD. By increasing the initiator concentration, conversion increases and final average polymer particle size drops, resulting in a broader PSD. The results show that by reducing the surfactant concentration, polymerization rate becomes slower and the final average polymer particle size increases, resulting in a narrower particle size distribution. The obtained results indicate that at higher temperatures, polymerization rate is higher leading to increase in total number of particles which leads to a smaller final average polymer particle size and a narrower PSD. In all cases good agreements are observed between simulation and experimental results.

Acrylamide (as monomer), N,N''-methylene-bis-acrylamide (as cross-linker), ammonium persulphate (as initiator), N,N,N'',N''-tetramethylethyldiamine (as accelerator), and aluminium nitrate salt were used to produce a low temperature polymeric gel-net, in order to tailor the particle size of alumina powder. The monomers/salt ratio, metal ion/monomers interaction, furnace atmosphere, thermal stability and pore size of polymeric gel-net are the key factors to control the alumina particle size. Mercury porosimetry data and transmission electron microscopy (TEM) micrographs indicated that increasing the monomers/salt ratio from 1/1 to 3/1 resulted in polymeric gel-net with smaller pore size, and hence, nanopowders with narrower particle size distribution. The X-ray diffraction (XRD) patterns for nanopowders exhibited the amorphous phases below 1100°C and a single phase α-Al2O3 above 1100°C. Thermal analysis showed that for pre-oxidized samples below 200°C polymeric gel-net possesses better thermal stability at higher temperature in the presence of inert gas. Trapping of metal ions, with specific coordination numbers, into polymeric gel-net pores prevents their migration and reduces the nanopowder particles agglomeration. These observations were also confirmed by Fourier transform infrared (FTIR) and UV-vis spectrometry measurments. Polymeric gel-net inhibits the aggregation of Al2O3 nanopowder, improves its homogeneity, and provides a powder with narrower particle size distribution.

Anovel chelating terpolymer resin has been synthesized by terpolymerization of anthranilic acid, salicylic acid and formaldehyde (ASF) in 1/1/2 molar ratios by condensation technique using glacial acetic acid as a reaction medium. The synthesized terpolymer resin was characterized by elemental analysis, FTIR, 1H NMR and 13C NMR spectroscopy. On the basis of spectral studies, the structure of the terpolymer resin was proposed. The physicochemical parameters have been evaluated for the terpolymer resin. Gel permeation chromatography was used to determine the average molecular weight and polydispersity of the ASF terpolymer resin and the viscosity-average molecular weight was also determined to compare molecular weights of the resins obtained. The thermal stability of the terpolymer was analyzed by thermogravimetric analysis. Kinetic parameters such as activation energy and the order of the reaction was determined using Freeman-Caroll method. The electrical property of the terpolymer was also evaluated at various concentrations and temperatures. The surface feature of the synthesized terpolymer was established by scanning electron microscopy. Batch equilibrium method was employed to explore the selectivity and binding capacity of the terpolymer resin towards certain divalent metal ions such as Pb2+, Zn2+, Cu2+, Mg2+ and Ba2+ in different electrolyte concentrations, wide pH ranges and different time intervals.