مجله ایرانی پلیمر
سال:1380 | دوره: | شماره: |تعداد مقالات:7

Radiation-induced copolymerization is a very promising method for the synthesis of polymers with the required combination of properties. It provides the possibility of controlling the copolymerization process and, thus, to obtain copolymers with the desired composition and molecular weight characteristics as well as copolymers with comonomers that are difficult to polymerize. This work deals with the characterization of radiation-induced copolymerization of N-vinyl-2-pyrrolidone (VP) with such comonomers: allyl alcohol and allylamine in bulk, in ethanol or isopropanol at 320 K and at an irradiation dose rate of 2 Gyls. It was established that by changing the characteristics of the irradiated medium (irradiation dose, composition and concentration of the initial monomer mixture and solvent nature) it is possible to obtain water-soluble reactive copolymers of VP with allyl alcohol and allylamine. Their molecular weights, Mw, are between 10-68x103, their molecular weight distribution is relatively narrow (MW/ Mn=1 .4-2.8) and they contain 12 .8-24.3 mol % of functional groups. The structure of these copolymers was confirmed by functional analysis and IR spectroscopy, Acute toxicity of these functional copolymers was investigated. Some of these copolymers in their principal characteristic meet the requirements that should be fulfilled by synthetic non-biodegradable polymers, modifiers of biologically active compounds. Specific examples are reported in using them as carriers of biologically active compounds with fungicidal activity.

A kinetic gelation model that incorporates the kinetic of non-linear free radical copolymerization of a mixture of bi- and tetrafunctional monomers is used to simulate the kinetics effects on polymerization statistics and microstructures. An algorithm for random next step selection in a self-avoiding random walk and efficient mechanisms of mobility of components are introduced to improve the universality of the predictions by removing commonly occurring simulation deficiencies due to early trapping of radicals. The model has the capability to account into several free radical polymerization mechanisms such as cross-linking, branching, and also to predict the onset of sol-gel transition, and the effect of chemical composition on the transition point. It is shown that a better understanding of microstructure evolution and appearance of gel phase during polymerization and chemical gelation is attained. Finally, one important benefit of the simulation method is the ability to produce a system of very highly packed random chains or clusters within a polymer network.

In this study the effects of enzymatic hydrolysis on drawn polyester filament yarns were investigated. Two multifilament yarns were drawn with different draw ratios at different temperatures and then they were hydrolyzed in similar conditions. The effects of hydrolysis were studied by means of measuring weight loss, moisture absorption, tenacity, elongation-at-break, IR spectrum and scanning electron microscope. Results of this research showed that the hydrolysis decreases the weight of polyester hanks by less than 0.5%. The strength loss due to hydrolysis reached a maximum of 10%, whereas the elongation-at-break of samples decreases by 7-25% due to hydrolysis. Hydrolysis also increased the moisture absorption of the polyester by up to 50%. The FTIR spectra as well as other results show that the effect of hydrolysis is limited to the surface of the substrate and hydrolysis is more affected by the increase in surface area rather than drawing.

Kinetics of thermal degradation of polylactic acid (PLA), a biodegradable and bioabsorbable polyester, under atmosphere of inert gas has been investigated. Isothermal and dynamic heating techniques of thermogravimetry have been used in this study. The weight loss data versus time were recorded at the temperatures of 180, 200, 220, 240, 260 and 280° C, in the isothermal heating experiments. Also, the weight loss data versus temperature were collected in dynamic heating runs conducted with the heating rates of 10, 15, 20 and 25 °C/min. Two kinetic models, one for isothermal and the other for dynamic heating experiments were utilized to fit the data. It is elucidated that the thermal degradation of PLA is a single stage process within the range 0-30% of weight loss, having activation energy of 21-23 kJ/mol.

The effect of filler loading and bonding agent on the dynamic properties and swelling behaviour of bamboo fibre filled natural rubber composites were carried out. Bamboo fibre was used as a filler and the loading range was from 0 to 50 phr. Dynamic properties were determined using a Monsanto moving die rheometer (MOR 2000) at 150°C. Results show that the maximum elastic torque (S"-MH) and minimum elastic torque (S 'ML) increase with increasing filler loading and the addition of bonding agent. However, the viscous torque (S" -MH) and tan Sae decrease with the addition of bonding agent. For swelling behaviour, the water absorption of the composites increases with increasing filler loading but decreases with the addition of bonding agent. The presence of bonding agent is found to improve the adhesion between bamboo fibre and natural rubber matrix as indicated by the tensile fracture surfaces of the composites using scanning electron microscope (SEM).

New linear polyurethanes (PUs) derived from bisl4 (6-hydroxynexoxy)phenyl)ether (HHPE) and tolylene diisocyanate were synthesized by melt step growth or solution polymerization . In conducting the process of polyadditon in solution at 80-90° C for about 4 h, NN-di-methylformamide as aprotic solvent, 1 wt % conc. of dibulyltin dilaurate as catalyst and -25 wt % conc. of monomers were used. We found rli, molecular weight (by GPC), and melting temperature for the reaction products. Thermal properties of the polymers were investigated by means of thermal gravimetric analysis and differential scanning calorimetry . The structure of the resulting products was confirmed by elemental analysis, Fourier transform infrared spectroscopy and X-ray diffraclometry. Segmented PUs were synthesized from variable amount of polytetramethylene oxide, tolylene diisocyanate and HHPE as chain extender in conditions established earlier for non-segmented PUs.

2,5-Norbornadiene has been polymerized in bulk at 125 °C in presence of a low molar mass of polystyrene-TEMPO as macroinitiator. The structure and poly-dispersity of the obtained diblock copolymer (PSt-PNB-TEMPO) were determined by IR,1 H NMR spectroscopy and GPC measurement, respectively, where TEMPO is 2,2,6,6 tetramethylpiperidinyl-1-oxy and PNB is polynorbornadiene. The triblock copolymer of styrene-2,5-norbornadiene-ethylmethacrylate (PSt-PNB-PEMA) using a PSt-PNB-TEMPO as the macroinitiator in the presence of camphorsulphonic acid (CSA) was prepared. Also the triblock. copolymer containing polyethylmethacrylate and poly(ethylene glycol) designated as PEMA-PEG-PEMA was synthesized by a novel method. The 1H NMR and FTIR studies of triblock copolymers confirmed their structures and the absence of TEMPO end groups for PEMA.