Iranian polymer journal
Volume:21 Issue: 4, 2012

In the past two decades, resorcinol–formaldehyde (RF) gels have found widespread applications owing to their low density and adjustable pore size. They are usually prepared through sol–gel polymerization of the monomers in an aqueous media followed by evaporative or supercritical drying. In this study, RF gels were synthesized via sol–gel polymerization in the presence of sodium dodecylbenzene sulfonate (NaDBS) followed by ambient and supercritical drying. Dimensional measurements along with N2 sorption analysis and Scanning electron microscopy (SEM) micrographs revealed that pore structure of the gel is chiefly affected by NaDBS. In all samples (xerogels and aerogels), maximum densities were observed at a critical NaDBS concentration (~1 w/v%), whereas considerable pore size increments and pore size distribution broadenings were found at higher concentrations of NaDBS (≥5 w/v%). The most increased mesopore volumes were detected in xerogels (133% for acetone-dried and 67% for water-dried samples), while concerning aerogels, the pore sizes enlargement to macropore regime was observed at 5 w/v% of NaDBS. SEM micrographs, in agreement with porosity analysis, depicted that very large pore volumes could be obtained when supercritical drying was employed. However, in the case of xerogels, a more dense structure with smaller pores (micro and mesopores) exists which can only be altered slightly when using large amounts of NaDBS. The results showed that the RF gel pore texture, independent of drying technique, was strongly influenced by the addition of NaDBS, which should be taken into account when using this surfactant in the gel formulation for a wide variety of applications.

A series of multiple cross-linking ultraviolet (UV) curable waterborne polyurethane dispersions (UV-PUDs) were synthesized by modification of diglycidyl ether of bisphenol-A-based epoxy resin (E51) through ring-opening by 3-aminpropyltriethoxysilane (APTES). Initially, APTES-E51 was synthesized using APTES to open the epoxy groups of E51. Then, APTES-E51 was incorporated into the chains of polyurethane, and multiple cross-linking UV-PUDs were produced. The chemical structures were confirmed by the Fourier-transform infrared spectroscopy (FTIR) and the effect of the APTES-E51 content on the UV-PUDs properties was investigated. The average particle size of UV-PUDs was determined by dynamic light scattering (DLS). The result showed that the average particle size increased with increasing APTES-E51 content and the stability of the UV-PUD storage diminished when the content of APTES-E51 was 10.0%. After modification by APTES-E51, the water absorption of the UV-cured films decreased and the water contact angle (CA) increased significantly. Thermogravimetry analysis (TGA) of the UV-cured films illustrated that APTES-E51 modified UV-curable waterborne polyurethane could exhibit good thermal stability. In addition, mechanical property of the cured films showed that the incorporation of APTES-E51 also improved tensile strength of the cured films. We can obtain good storage stability, satisfied water resistance, and high thermal stability and tensile strength when the APTES-E51 content of the UV-PUD was 9.1%.

In this work, the influence of SiAlON nanoparticles loading level (0–12 wt%) was investigated on the mechanical and chemical properties of epoxy resin-based nanocomposites coatings. The samples were characterized by fracture toughness, chemical, pull off, hardness and abrasion tests, followed by scanning electron microscopy of the fracture surfaces and sample surface after performing a chemical test. Nanoparticles were also characterized by transmission electron microscopy and linear light scattering analysis techniques. Epoxy resin coating based on bisphenol A was treated with polyamine hardener as a curing agent. Fracture toughness measurements were carried out using a single edge notched bend specimens within a three-point bending test at room temperature. Effect of SiAlON nanoparticles on the chemical resistance of epoxy resin was investigated by immersion of samples in 3.5 wt% NaCl solution at 85 °C for 60 days. Results indicated the enhancements in the mechanical properties and chemical resistance of epoxy nanocomposite due to the addition of small parts of SiAlON nanoparticles. The contents of samples with 3 and 5 wt% of SiAlON nanopowders have been considered as optimum contents compared to the other samples. They showed improvement in the crack propagation resistance in chemical solution and fracture toughness tests, both. Enhancment in abrasion resistance was found at either of 3 and 5 wt% SiAlON epoxy nanocomposite samples where they showed 59 and 34% abrasion resistance more than that of the neat resin, respectively.

This study aims to fabricate and formulate a new magnetic resonance imaging (MRI) contrast agent based on a dextran–spermine nanoparticulate system loaded with super paramagnetic iron oxide nanoparticles (SPION). SPION-loaded spermine–dextran nanoparticles were prepared according to a procedure based on the ionic gelation of dextran–spermine with sodium tripolyphosphate (TPP) anions. The effects of process parameters such as pH, concentration of spermine dextran, TPP to dextran–spermine and SPION to dextran–spermine weight ratios, and TPP addition rate were fully investigated to find the optimized formulation through the response surface methodology. At the optimum condition, 75% of the magnetic iron oxide nanoparticles added to the polymeric solution were entrapped in dextran–spermine nanoparticles. Samples were investigated by transmission electron microscopy. The mean particle size of the nanoparticles determined by particle size analyzer was found to be 65 nm at the optimum condition with zeta potential of +90 mV. The SPION-loaded dextran–spermine nanoparticle formulation has the same superparamagnetic properties as SPIONs and at same iron concentration the saturation magnetization (Ms) of the SPION-loaded dextran–spermine nanoparticles was larger than SPIONs. In vitro MRI was performed with gradient echo and spin-echo sequences at 1.5 T. By increasing of iron concentration, the T 2 relaxation times were reduced. Thus, indicating that the saturation magnetization and r 2 and relaxivities were enhanced, and the contrast effects were improved in comparison to commercial SPIONs.

A pH-responsive triblock copolymer of poly (acrylic acid) -b-poly (ethylene glycol) -b-poly (acrylic acid) containing hydrophobic dodecyl end groups (C12H25-PAA-b-PEG-b-PAA-C12H25) with narrow molecular weight distribution (M w/M n = 1. 30) was synthesized via reversible addition-fragmentation chain transfer polymerization of acrylic acid (AA). Poly (ethylene glycol) (PEG) capped with S-1-dodecyl-S′- (α،α′-dimethyl-α″-acetic acid) trithiocarbonate (DDATC) end groups was used as the macro chain transfer agent (PEG macro-CTA) and 2،2′-azobisisobutyronitrile (AIBN) as initiator for monomer acrylic acid. The effect of the hydrophobic dodecyl end groups on pH-sensitive self-association of C12H25-PAA-b-PEG-b-PAA-C12H25 in aqueous solution was investigated by fluorescence spectroscopy، dynamic light scattering and atomic force microscope. At pH ≥5. 5، the solution behavior of C12H25-PAA-b-PEG-b-PAA-C12H25 is like polyelectrolyte in aqueous solution، and the effect of dodecyl end groups is negligible. At pH <5. 0، the hydrophobic dodecyl end groups contribute dominantly to the pH-sensitive micellization and result in the formation of micelles with stronger hydrophobicity and larger size at low concentration (critical micelle concentration is 0. 062 g/L). In the range of pH 2. 5–3. 5، the steady (R h ≈ 35. 0 nm) and narrow size distributed micelles (polydispersity index، PDI < 0. 2) can be obtained. The micelles formed by C12H25-PAA-b-PEG-b-PAA-C12H25 triblock copolymer in acidic solution are expected to have a core–shell–corona structure، where the hydrophobic dodecyl groups form the core، and weak hydrophobic PAA/PEG hydrogen-bonded complexes form the shell and the uncomplexed PAA، and PEG chain segments form the corona.

The bio-based shape memory hyperbranched polyurethanes (HBPUs) have attracted tremendous attention both from academic and industrial researchers due to their strong potential in biomedical and other advanced applications. In the present investigation HBPUs have been synthesized from poly(ε-caprolactone)diol as a macroglycol, butanediol as a chain extender, triethanolamine as a branch generating moiety, monoglyceride of Mesua ferrea L. seed oil as a bio-based chain extender, at different percentages and toluene diisocyanate by a two step one pot A2 + B3 approach. The structure of the synthesized hyperbranched polyurethane was characterized by FTIR, IH NMR, XRD and SEM studies. 1H NMR study indicates the formation of highly branched structure with degree of branching 0.93 for polyurethane with 5 wt% monoglyceride. TGA results indicated the increment of thermal stability from 185 to 240 °C with the increase of monoglyceride content from (0–15) wt% for the HBPUs. The shape memory effect of the hyperbranched polyurethane increased with the increase of monoglyceride in the polymer. However, mechanical properties like tensile strength and elongation at break decreased from 19.31 to 11.48 MPa and 835 to 497%, respectively, with the increase in amount of bio-based component. Excellent impact strength and very good chemical resistance were also observed for the hyperbranched polymers. The studied bio-based HBPUs exhibit excellent shape fixity (95–99)% as well as shape recovery 100%. Thus, the studied HBPUs have the potential to be used as advanced shape memory materials.

In this work, nano-sized fumed silica (SiO2) was embedded in poly(methyl methacrylate) (PMMA)–poly(vinyl chloride) (PVC) blend with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl imide) (BmImTFSI) as ionic liquid. These composite polymer electrolytes (CPEs) were prepared by solution casting technique. The samples followed Arrhenius behavior in the temperature-dependence of ionic conductivity and further proved the ionic hopping mechanism in the polymer electrolyte. It is suggested the formation of three-dimensional polymer network among the aggregates weakens the interaction of polar group of the polymer backbone and initiates the ionic decoupling process. The mobile ions from adjacent sites would occupy this vacant site and reform the interactive bond with the polymer backbone whereby the ionic hopping mechanism is generated. The activation energy (E a) is further determined. The higher the ionic conductivity, the lower the activation energy. The maximum ionic conductivity of (8.26 ± 0.02) mScm−1 was achieved at 80 °C upon inclusion of 8 wt% of SiO2. X-ray diffraction (XRD) analysis revealed the higher amorphous region with increasing SiO2 mass loadings. The coherence length is further determined by using Debye–Scherrer equation. Higher amorphous region in the polymer matrix is conferred by showing the lower coherent length. Scanning electron microscopy (SEM) was applied to examine the morphology of polymer electrolytes. Based on the differential scanning calorimetry (DSC) study, glass transition temperature (T g) and melting temperature (T m) were decreased. Highly flexible polymer chain is produced when the T g was lowered down. On the other hand, thermal stability of polymer electrolytes was increased by SiO2 dispersion, as depicted in thermogravimetric analysis (TGA).