Iranian polymer journal
Volume:15 Issue: 12, 2006

The graft copolymerization of sodium acrylate onto chitosan in alkali medium was investigated, using redox system, potassium diperiodacuprate(III) (DPC) chitosan. The graft copolymer was characterized by Fourier transform infrared spectra analysis, X-ray diffraction analysis, differential scanning calorimetric, thermogravimetric analysis, and scanning electron microscopy techniques. A tentative mechanism is proposed to explain the generation of radicals and the initiation. The effects of reaction variables, such as the initiator concentration, the ratio of monomer to chitosan, and pH, as well as, reaction temperature and time were investigated, and the grafting conditions were optimized. Graft copolymer with high grafting efficiency was obtained, which indicated that DPC chitosan redox system is an efficient initiator for this graft copolymerization. The graft copolymer was used as the compatibilizer in blends of poly(methyl methacrylate) (PMMA) and chitosan. The scanning electron microscope micrographs indicated that the graft copolymer improved the compatibility of the blend. At the same time, the blend is expected to improve the biodegradability of the PMMA.

Transportation of crude oil near or below its pour point requires a deep understanding of crude oil chemistry, its rheological properties, and operating conditions. Out of all the methods available for pumping waxy crude oil, use of pour point depressant (PPD) is preferred economically. Optimization of PPD dosages can affect cost savings. Present study deals with the synthesis of copolymers of maleic anhydride and esters of nalkyl alcohols with oleic acid and methacrylic acid. The resulted copolymers were esterifiedwith two moles of fatty alcohol (C19H36O3). They were characterized by IR spectroscopyand their molecular weights were determined by GPC. These polymeric diesters with pendant fatty chains were evaluated for their efficiency as pour point depressants and flow improvers on crude oil from Gandhar oil field (Gujarat, India). The polymeric diesters of oleic acid series were found to be more effective and depress the pour point of the crude oil up to 9oC with 500 ppm of doses. The rheological properties of the crude oil such as apparent viscosity, plastic viscosity, and yield values were also studied using Fann V-G meter. The virgin crude oil above the pour point temperature was found to behave as Newtonian fluid and at the pour point it shows Bingham plastic behaviour. Different doses (100, 500, and 1000 ppm) of synthesized polymeric additives were examined at different temperatures with the crude oil to evaluate pour point depressants and to study the dependence of shear rate on its shear stress and viscosity. The additives of polymeric diesters (DO series) were evaluated as PPD and rheological modifiers. The mechanism of pour point depression and viscosity reductions are also discussed.

Most polymer blends are immiscible and need to be compatibilized. Compatibilization can be accomplished either by addition of a compatibilizer or by reactive processing. Grafting has been the most common method for compatibilizing two immiscible polymers during reactive processing. In this work, the reactive blending of EPDM (ethylene- propylene-diene monomer) rubber and SAN (styrene-acrylonitrile) copolymer was studied. The blends were prepared in an internal mixer with three types of organic peroxides as initiator. The effects of initiator type and concentration, EPDM content, and mixing sequences of components were investigated. Blends were separated to their structural components (i.e., SAN, EDPEM, SAN-g-EPDM, and gelled EPDM) which were then characterized by FTIR spectroscopy and SEM microscopy techniques. Mechanical properties including tensile and impact strength as well as elongation-atbreak were measured. From the three initiators used, the blends which have 2,5- dimethyl-2,5-di-(t-butyl peroxy) hexane as initiator show better mechanical properties. Also, SEM studies reveal a good compatibility for SAN/EPDM blends using this initiator. The blend using 40 wt% of EPDM of the mentioned initiator contains 16.24 wt% SANg- EPDM. Impact strength of the blends was affected by mixing sequences of the components. The Blends prepared by mixing sequences of SAN/initiator/EPDM show the highest impact strength of the order of 45 J/m.

Investigation on rheological properties of a reaction injection moulding polyurethane formulation was performed during the formation reaction. The effect of reaction temperature on the gelation time was studied in a wide temperature range covering temperatures below and above the gelation temperature. The gelation temperature and gel times were determined using the results of temperature sweep and time test experiments by employing rheological criteria. The results indicated that a noticeable increase has been occurred in the activation energy of gelation process at gelationtemperature. The shear rate dependency of the reactive mixture was also studied inlinear and non-linear viscoelastic domains. The viscosity of the reacting formulationexhibited shear thinning behaviour in both viscoelastic regions. By superimposing thecurves of shear viscosity in non-linear viscoelastic domain and the complex viscosityin linear viscoelastic region, it was found that the formed network-like structureremained intact under the shear rate in non-linear viscoelastic region. Moreover theseresults showed that by progression of the reaction the shear viscosity deviated to highervalues with respect to complex viscosity. This was attributed to the effective role ofconvective movements in non-linear viscoelastic regime. Convective movements ledto mobility increase of functional groups at high viscosities where the Brownianmotions are drastically retarded.

Miniemulsions of styrene with sodium dodecyl sulphate (SDS) as the surfactant and hexadecane (HD) as the co-stabilizer were prepared and polymerized. The on-line conductivity measurements were employed to characterize the emulsification by ultrasonication. Both the dynamic light scattering (DLS) and the transmission electron microscopy (TEM) were employed to determine the droplet and the particle size. The effects of various reaction parameters on the droplet (or particle) size and the polymerization kinetics were investigated. These parameters include the sonication time and the concentrations of SDS ([SDS]), potassium persulphate ([KPS]), and HD ([HD], as weight percent with respect to monomer). Moreover, their influence on the droplet nucleation was also discussed. It is shown that a critically steady state can be obtained after ultrasonicating the emulsion system for at least 24 min and relatively stable miniemulsions were prepared. The polymerization rate of miniemulsions increases with the increase in [SDS], [HD], and [KPS] due to different mechanisms, and the rate is faster than that of the corresponding macroemulsions. In addition, the predominant droplet nucleation is achieved in current miniemulsion systems and the required condition is concluded. Finally, nanosize polystyrene latexes were synthesized.

Aseries of oil gels based on the rigid hydrophobic monomer 4-tert-butylstyrene (tBS) and the soft oleophilic monomer ethylene-propylene-diene (EPDM) crosslinked with divinylbenzene (DVB) were synthesized by suspension polymerization. Effects of EPDM and DVB contents on swelling behaviours, compressive properties, effective cross-link density (e), average molecular weight between cross-links (Mc), and polymer-solvent interaction parameter (X1) of oil gels were studied. It has been shown that the equilibrium oil absorbency (Qeq) is first increasing and then decreasing with the increase of EPDM contents in polymerization, as well as Mc values. On contrary, the values of e first rise and then decline with the increase of EPDM contents, as well as the volume fraction of polymer in gel (r) and X1 values. The optimum reaction conditions are EPDM content 60 wt% and DVB content 3 wt%. Further increase of DVB content leads to changes of swelling behaviour, network structure and polymer-solvents interaction in oil gels, viz. the decrease of Qeq and Mc values, the increase of r, e, and X1 values. These changes represent macroscopically the varieties of compressive strength and Young''s modulus of the oil gels. The comparison between efficient cross-linking density and theoretical cross-linking density (t) indicates that the double bonds in EPDM monomeric unit has participated in chemical cross-linking, and the physical cross-linking and entanglements have thr weakening effects on chemical cross-linking.

Living polymerization of styrene initiated with benzoyl peroxide (BPO) in the presence of 2,2,6,6-tetramethyl piperidine-N-oxyl (TEMPO) at 125°C was performed by using nitroxide-mediated living radical polymerization (NMRP) technique. The obtained TEMPO-ended polystyrene served as macroinitiator for the synthesis of poly(styrene-block-vinylpyrrolidone) diblock copolymer. Also, by polymerization of the mixture of styrene and N-vinylpyrrolidone in the presence of TEMPO and BPO, random copolymers of these monomers were prepared at different feed ratios by NMRP technique. The microstructure of synthesized polymers is investigated by 1HNMR and IR spectroscopies and GPC techniques. The compositions of synthesized polymers were investigated by elemental analysis and the reactivity ratios of these monomers were calculated by using the elemental analysis data through Fineman-Ross equation, which were 15.509 and 0.102 for styrene and N-vinylpyrrolidone, respectively. The solubility of synthesized diblock and random copolymers are investigated in various solvents, and the results showed the amphiphilicity of synthesized copolymers.