Iranian Polymer Journal
Year:2011 | Volume:20 | Issue:3 (129)|Papers Count:8

Polymeric organogels, macromolecular networks with ability to imbibe polar or non-polar organic solvents, have recently been attracted by both academy and industry. These materials (called also polymer organogelator) can convert an organic liquid to a solid gel. Alcohol specific super-swelling organogels (i. e. , superalcogels) can be used for various applications such as fuel gels or pharmaceutical formulations. In this paper, super-alcogels were synthesized using a macromonomer (macromer), polyethylene glycol methylether methacrylate (PEGMA), and an ionic monomer, 2-acrylamido-2-methylpropane sulphonic acid (AMPS), through solution polymerization using a persulphate initiator and a macromeric cross-linker (polyethylene glycol diacrylate). The copolymers exhibited very high absorbency of various monohydric and polyhydric alcohols including methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, 1, 3-propane diol and glycerol. For example, a typical sample imbibed ethanol and methanol as high as 33 and 36 g/g, respectively. It was found that several parameters had influence on swelling of an organogel such as: dielectric constant of the solvent, the alcohol OH/C (as a simple measure of the hydrophyl/organophyl ratio) and the isomeric position of hydroxyl group in the alcohol chemical structure. The dissociating ability of the ionic groups (i. e. , SO3H groups) was recognized to be mainly affected by dielectric constant of the solvent. Higher AMPS content in the alcogel structure improved alcohol absorbency because of increased sulphonic acid mobile ions in the gel phase. Thermal and mechanical properties of these copolymers were also studied. Glass transition temperature of the copolymer was decreased with increase of the macromer and the samples with high macromeric content showed elastomeric behaviour at room temperature in dry state. Thermal stability was improved with lowering of AMPS content due to susceptibility of sulphonic acid group at lower temperatures.

Anovel physically cross-linked, injectable poly (N-acryloylglycine) (PNAG) hydrogel was synthesized based on glycine. The molecular structures of the corresponding monomer and polymer have been confirmed by FTIR and 1H NMR measurements. The sol-gel transition behaviours of PNAG in its aqueous solution were evaluated using test tube-inversion method, as a function of PNAG concentration, pH and ionic strength. PNAG showed a remarkable injectability originating from the H-bonding interaction among amide and carboxyl groups in PNAG chains and water molecules. The swelling behaviours of hydrogel PNAG were systematically investigated at different temperatures and PNAG concentrations. It was found that the PNAG hydrogel demonstrates distinct temperature responsive nature. Using caffeine as a model drug, in vitro drug release behaviour showed that the release rate of caffeine from PNAG hydrogel apparently dropped as PNAG concentration of the system was increased, while the temperature and pH decreased. The amount of caffeine released from PNAG hydrogel, within 120 min, was 69% at room temperature, whereas 88% caffeine was diffused into the medium at 37°C. In addition, PNAG has shown a certain degree of degradability at pH 2.2 of phosphate buffered saline. In this respect, PNAG hydrogel seems to become a promising injectable material in the biomedical field due to its injectability and degradability potentials.

This study involved the optimization of determining parameters in reaction conditions of carboxymethylation process of sago starch (metroxylum sagu) against degree of substitution (DS) and reaction efficiency (RE%). Characterizations were carried out by analyzing the spectrum of Fourier transform infrared (FTIR), the thermograms of differential scanning calorimetry (DSC), the X-ray diffraction (XRD) patterns, the scanning electron microscopy (SEM) photomicrographs and viscosity analysis. The optimized reaction conditions were determined by the amount of sodium hydroxide in the system, the time taken for a complete reaction, the temperature used for the reaction to occur and the ratio of the anhydroglucose unit to sodium monochloroacetate produced in the final yield of the product. The optimized reaction conditions of 20% concentration of NaOH, reaction time of 1 h, reaction temperature of 55°C and NaMCA: AGU molar ratio of 1.5: 1.0 produced a DS value of 1.05 and RE of 85.9% carboxymethylated sago starch. The FTIR spectrum clearly displayed the new peaks at 1587 cm-1 and 1416 cm-1, which indicated the presence of carboxymethyl group. SEM Photomicrographs showed starch granules being distorted, the surfaces were rough and grooved compared to the native starch granules indicating an acid or enzyme-treated reaction took place. The DSC thermograms exhibited an endothermic peak for sago starch but none for the treated sago suggesting the absence of gelatinization, which was later confirmed by the changes of the XRD patterns. These optimization factors allowed higher yields of carboxymethyl sago starch providing plenty of opportunities for its multi-applications.

Arobust Monte Carlo simulation as a stochastic random-based method was employed to study the bulk photopolymerization of furfuryl methacrylate (FM) at various temperatures. An appropriate mechanism of polymerization considering a vast variety of reactions was selected and therefore, a reliable algorithm was designed. In addition, experimental results were used to evaluate the simulation procedure and algorithm and consequently, confirm the simulation results. The concentration profiles of different species with respect to irradiation time were obtained by this simulation method. In addition, the effect of temperature variation on the concentration of species has been evaluated. At higher temperatures, an increase in the rate of FM consumption was revealed which is because of an increment in the propagation rate constants of acrylic macroradicals. At 40°C of the early stages of the photopolymerization, M1* concentration increases rapidly with respect to irradiation time; this is on account of the superior primary initiation constants compared to other temperatures. However, due to the acrylic macroradicals termination, intermolecular degradative transfer, allylic-acrylic termination and acrylic primary termination, M1* concentration reaches a plateau. Moreover, the highest concentration of M1* was achieved at 0°C. A data analysis based on the least square method was performed to evaluate the FM concentration and consequently, a reliable agreement between the experimental data and the Monte Carlo simulation results were obtained at different temperatures.

Stereoregularity and microstructure of polystyrene (PS) were investigated by split para carbon of the benzene ring demonstrated by 13C nuclear magnetic resonance (NMR) spectroscopy. Polystyrene was synthesized via bulk thermal polymerizations at 50, 150 and 250°C at low conversions. Assignment of all the peaks of para carbon in a triad sequence was achieved. Bernoullian statistics was applied for three PS samples and by comparing the experimental and theoretical results it is found that with increasing polymerization temperature the probability of meso is augmented. Furthermore, with increasing NMR acquisition temperature from 20 to 65°C, triad sequences were converted to pentad sequences which follow 1st-order Markov statistics. Finally, it is shown that different deuterated solvents and their mixtures affect peak resolution and splitting of syndiotactic and isotactic sequences. To investigate the effect of deuterated solvent, deuterated benzene and tetrahydrofuran (THF-d8) were also used and the spectra of polystyrene para aromatic carbon of benzene ring in these solvents were compared. There are three peak regions in CDCl3 at 20°C while, in THFd8, syndiotactic region is almost separated and isotactic region overlaps with the atactic region, and in C6D6 both syndiotactic and isotactic regions overlap. As a result, motions of racemic rich segments in THF-d8 are higher than those of meso and conversely the mobility of racemic rich segments in CDCl3 is lower than that of meso rich segments. In summary, in THF-d8 the upfield regions and in CDCl3 the downfield regions show better splitting.

Aseries of poly (1-octene-co-t-butyl acrylate) were prepared by conventional free radical polymerization under mild conditions. The influence of different hightemperature decomposition initiators (e. g. , t-butyl peroxybenzoate, di-t-butyl peroxide) on copolymer composition was above all investigated. Subsequently, poly (1- octene-co-t-butyl acrylate) was hydrolyzed to form amphiphilic poly (1-octene-co-acrylic acid). Thermal behaviours of poly (1-octene-co-t-butyl acrylate) and poly (1-octene-coacrylic acid) and micellar behaviours of poly (1-octene-co-acrylic acid) in water were investigated. By using high-temperature initiators the copolymerization temperature can be increased which results in incremental incorporation of 1-octene and monomer conversion.1-Octene incorporation can be regulated in the range of 0~37.1 mol%. Meanwhile, molecular weights of these copolymers decreased as copolymerization temperature increased. The reactivity ratios of 1-octene (r1) and t-butyl acrylate (r2) were figured out as r1=0.005±0.001 and r2=9.016±0.035. CMC Value of poly (1- octene-co-acrylic acid) in water increased as their molecular weight and 1-octene incorporation were lowered. However, the mean hydrodynamic radius decreased as molecular weight increased or 1-octene incorporation dropped. Although Tg value of poly (1-octene-co-acrylic acid) is much higher than that of poly (1-octene-co-t-butyl acrylate), they all drop with the lowering of molecular weight or the increased 1-octene incorporation.

Polylactide as a valuable biodegradable polymer is being widely investigated with respect to its synthesis, physical properties, biodegradation and application. The aim of this study is to evaluate hydrolytic degradation of poly (l-lactide) (PLLA) in the presence of added l-lactide dimer. High molecular weight PLLA was synthesized in presence of stannous octoate through the ring opening polymerization of l-lactide. PLLA films, containing 0, 1, 3 and 5% (w/w) l-lactide (as additive), were prepared by solution casting. In vitro degradation of the PLLA matrices were carried out in distilled water at 37°C for the definite periods. The degraded polymer matrices have been characterized by SEC, SEM and DSC techniques after periods of 3 and 6 months degradation time. It was found that during the first 3 months of degradation period, the number average molecular weight (¯Mn) of each PLLA film containing l-lactide reduced slower than the control sample. Also, it is shown that the films containing l-lactide have higher crystallinity and melting point in comparison with non-containing l-lactide samples. However, after 6 months, degradation rate of PLLA matrices containing l-lactide increased due to penetration of water by eluting and removal of l-lactide from PLLA matrices.

Typical blocked isocyanate systems are used to obtain the performance of two-component polyurethane system in a one-component mixture. In this study a blocked adduct was synthesized by 2, 4, 6-trichlorophenol (TCP) as blocking agent for polyaryl polyisocyanate (PAPI). This blocking reaction was in the presence or absence of the catalyst (dibutyltin dilaurate, DBTDL). Elimination of the isocyanate groups and the formation of urethane bonds were studied by FTIR spectroscopy and titration methods. FTIR Spectrum indicates that the NCO groups of the isocyanate molecule are blocked with TCP and the added catalyst should make the reaction faster than that of un-added catalyst. The blocked adduct was characterized by 1H NMR, 13C NMR, DSC and TG/DTA. The 1H NMR and 13C NMR spectra of blocked adduct demonstrated that the structure of the carbamate was observed. Thermal dissociation of blocked diisocyanates was analyzed by DSC and TG/DTA techniques. Deblocking temperature obtained by DSC and TG/DTA techniques was compared. Based on DSC data, it was found that deblocking of blocked PAPI started at 75°C. In general, TG/DTA results showed the same trend as DSC. Deblocking temperature value obtained by TG/DTA technique was lower than DSC value. Differential thermal analysis showed the blocked PAPI began to deblock at 70°C.