Iranian polymer journal
Volume:17 Issue: 10, 2008

Cross-linking starch microsphere (CSM) is a derivative of crude starch and has been studied and applied widely in the fields of medicine and sanitary devices. In our studies we have found that starch microsphere has good adsorption performance to metal ions in water. In this work, a type of cross-linking starch microsphere has been synthesized by reversed phase suspension method using soluble starch as raw material with N,N''-methylenebisacrylamide as a cross-linking agent. The observation through scanning electron microscopy (SEM) shows that CSM is a homogeneous mixture of spherical particulates with heterogeneous surface with particles'' average diameter of about 50 μm. The structure characteristics of carbonyl group and second acylamide in Fourier transform infrared spectroscopy spectrogram of CSM demonstrates that the soluble starch is definitely cross-linked with N,N''-methylenebisacrylamid. The synthetic analysis of X-ray diffraction indicates that the cross-linking function decreases the crystallinity of CSM compared with that of soluble starch. The adsorption capacity of CSM towards Cu2+, Co2+, and Ni2+ increases with the increase in metal ion concentration, and by lowering the temperature, adsorption can be accelerated. The adsorption behaviour of CSM in different temperatures is in agreement with the Freundlich isothermal equation. The research results show that the adsorption process is exothermic, can proceed spontaneously, with the adsorption force mainly derived from enthalpy changes. The thermodynamic parameters of adsorption process show that the adsorption behaviour of CSM towards Cu2+, Co2+, and Ni2+ is of a physical type.

Open circuit thermally stimulated current (TSC) and surface charge decay measurements have been carried out on the 30 μm thickness samples of pristine and iodine doped polymethylmethacrylate (PMMA) to understand the nature of decaying charge. The samples are thermally charged at different temperatures with different polarizing fields. Both types of charges, hetero- and homo-charges are present in iodine doped PMMA samples, however, only hetero-charges are observed in pristine PMMA samples. A double charge reversal from hetero- to homo-charges and homo- to hetero-charges is observed in few cases of iodine doped PMMA samples. A single anomalous TSC peak is appeared in iodine doped PMMA when polarized at high field and temperature. The appearance of anomalous current in the high temperature region is in agreement with the double charge reversals (i.e., hetero- to homo-charges and homo- to hetero-charges) observed in surface charge decay study and TSC measurments. This could be explained on the basis of high return rate of the charge carriers released from the traps. However, this behaviour of TSC is inherent in pristine PMMA samples. The observed behaviour of surface charge decay and TSC have been explained in terms of the existence of hetero-charge due to dipole orientation and ionic space charge drift, together with an injection of charge carriers from an electrode and subsequent localization in surface and bulk trap.

Dynamic rheological behaviour and mechanical properties of neat and reactive LDPE/PDMS immiscible blends were investigated, focusing on low frequency data analysis as an approach for microstructural characterization. It was observed that by analyzing low frequency data, some microstructural features such as development of continuity in the minor phase and occurrence of interfacial slip phenomenon of neat blends could be revealed. Development of continuity in the minor phase, as proved by SEM micrographs, resulted in a significant increase in low frequency values of η′ and η″ while interfacial slip phenomenon was inferred by comparing the rheological data with predictions of log-additivity and inverse mixing rules. To induce reactive blending, different amounts of DCP as curing agent was added to PDMS phase. By studying the influence of reactive blending on thermal behaviour and viscoelastic properties in low frequency region it is revealed that curing reaction during melt mixing could lead to formation of an interphase layer which acts as an efficient compatibilizer between the phases. Thus, reactively compatibilized blends exhibit desirable tensile properties.

The resin was synthesized by condensation of 2-hydroxy-4-ethoxyacetophenone with 1,4-butane diol in the presence of polyphosphoric acid as a catalyst at 145ºC for 10 h. The synthesized resin was used to synthesize its polychelates with 4fblock elements. The resin and its polychelates were characterized on the basis of elemental analyses, electronic spectra, magnetic susceptibilities, FTIR, NMR, and thermogravimetry analyses data. Morphological studies of the resin and its polychelates were carried out by scanning electron microscope (SEM). Number average molecular weight (Mn) was measured by vapour pressure osmometry (VPO). Adsorption studies at different electrolyte concentrations, pH, and rates have been carried out for 4f-block elements in the resin. It s observed that, the resin can be used as an efficient adsorption agent.

Anovel ABC triblock copolymer of poly(ethylene oxide)-b-poly(styrene)-b-poly(4- vinylpyridine) (PEO-b-PS-b-P4VP) was successfully synthesized via atom transfer radical polymerization (ATRP). First, polyethylene glycol monomethyl ether (PEO) terminated with a halogen atom (PEO-Br) was prepared by esterification of PEO with 2-bromoisobutyryl bromide. Next, bromo-terminated poly(ethylene oxide)-bpoly(styrene) (PEO-b-PS) diblock copolymers were obtained by the polymerization of styrene using PEO-Br as the macroinitiator and CuBr/bpy complex as the catalyst. Finally, PEO-b-PS-b-P4VP triblock copolymers were also prepared by ATRP of 4- vinylpyridine (4VP) using PEO-b-PS-Br as the macroinitiator and CuCl/ tris[2-(dimethylamino) ethyl]amine (Me6TREN) as the catalyst. The triblock copolymers and precursors were characterized by 1H NMR spectroscopy and gel permeation chromatography (GPC) techniques. The triblock copolymers prepared by this method have a welldefined structure. The results of GPC analysis showed that the as-prepared triblock copolymers had relatively narrow molecular weight distributions. The kinetics of copolymerization was also investigated. The results indicated that the ATRP process of 4VP is "living"/controlled in 2-propanol at conversions below 70%.

Instead of the traditional two-step method with cyclic intermediates, a direct reaction of D,L-lactic acid (D,L-LA) and glycine (Gly) as monomers (molar feed ratio LA/Gly: 90/10) and SnO (0.7 wt%) as catalyst is carried out to synthesize a biodegradable poly(lactic acid-co-glycine) [P(LA-co-Gly)] via melt copolycondensation at 170°C, absolute pressure of 70 Pa, for 8 h, following a prepolymerization step. The structure of the copolymer was characterized by FTIR and 1H NMR techniques. The GPC results show that the weight average molecular weight (Mw) of the copolymer P(LA-co-Gly) is 3600 g/mol. Under the condition of different molar feed ratios the highest Mw was found to be 5200 with molar feed ratio LA/Gly:98/2. Other characterizations, e.g., intrinsic viscosity, solubility, DSC, and XRD indicated that the copolymer solubility in chloroform and tetrahydrofuran (THF) decreased with the increasing feed charge of Gly and the lowest solubility was found when the molar feed ratio was below LA/Gly:70/30. However, the modified polylactic acid is readily soluble in DMSO. The crystallinity of copolymer gradually disappears as the molar feed ratio of D,L-LA decreases. For LA/Gly ≥ 90/10, the XRD pattern has two diffraction peaks, close to 16.8° and 19.1°, the same position as poly(D,L-lactic acid) (PDLLA). For the soluble P(LA-co-Gly) the intrinsic viscosity, Mw and its dispersity (Mw/Mn) decrease gradually with the increase of feed charge of Gly. These results, especially the molecular weight of the copolymer appear to meet the requirements necessary for a drug delivery applications.

The effects of galbanic acid (GA) (a type of coumarin derivative) on the thermal and thermo-oxidative stabilities of LLDPE were investigated using thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy techniques. It was shown that GA does not modify the onset of thermal degradation of the polymer. However, the thermo-oxidative stability of the polymer has been improved significantly in the solid state and moderately in the melt state by the additive. There is a proportional relationship between the stabilization effect of GA and its concentration in the polymer. Comparing the thermal resistance of LLDPE samples containing a combination of GA and a commercial antioxidant for polyethylene, Irganox 1010, and the samples containing Irganox 1010 alone confirmed that GA does not reduce the stabilization efficiency of the phenolic antioxidant in the polymer either in the melt or in the solid state. It was also observed that coumarin which was used in this study as a representative of the unsaturated lactone moiety of GA molecule has no contribution in GA stabilizing activity. On the basis of the obtained results, the thermo-oxidative stabilizing activity of GA was described in terms of the activity of allylic hydrogens present in the substituted moieties of GA molecules.