Effect of methyl position on the dynamic mechanical and shape‐memory properties of cresol‐based polybenzoxazines

Three difunctional benzoxazines were synthesized from cresol isomers (o‐, m‐, and p‐methylphenols), 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetramethyldisiloxane, and formaldehyde. The ring‐opening polymerization temperature decreases in the order of ortho‐, para‐, and meta‐positions of methyl group for the benzoxazine monomers, whereas the glass transition temperature increases in the order of ortho‐, para‐, and meta‐positions of methyl group for the resultant polybenzoxazines. In addition, the polybenzoxazines exhibit one‐way dual‐shape‐memory behavior in response to changes in temperature, and the shape‐memory effects are evaluated by tensile and bending tests with a temperature program based on glass transition temperature. The o‐ and p‐cresol‐based polybenzoxazines exhibit higher shape‐memory performance than their m‐cresol‐based analogue/counterpart. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45443.     

Role of bismuth oxide as a reinforcer on gamma shielding ability of unsaturated polyester based polymer composites

Unsaturated Polyester resin is reinforced with Bi₂O₃ up to 60% filler weight. The effect of bismuth oxide on gamma shielding ability of the composites is studied in terms of attenuation parameters using Ba‐133, Cs‐137, and Co‐60 gamma ray sources. The results reveal that, the shielding property of the composite material increases with increase in the filler concentration and decreases with energy. The HVL, TVL, and relaxation length of the composites are found to decrease with increase in the filler concentration. It is found that, the shielding ability of 60% filled polymer composite is comparable to that of barite at low energy. The above polymer composite performs well at all energies and can act as an excellent gamma radiation shield for low energies and also proved to be light weight when compared to the conventional shielding materials. Thus, the gamma shielding ability of the UP resin is enhanced due to the addition of Bi₂O₃. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44657.     

Sealing system activated by magnetic induction polymerization

This work describes the one‐step production of glycerin based polyurethane/magnetite nanocomposites. The polymerization was performed in a nonaqueous dispersion containing the magnetic nanoparticles and the polar monomers under alternating magnetic field. Fourier transform infrared spectroscopy and crosslink degree tests were useful to conclude that the use of magnetic induction (～3 min at 9300 W) produced results similar to the ones obtained by the conventional polymerization (～3 h at 80 °C) in a fraction of the required time. A lost circulation fluid control test also was performed under magnetic induction heating and the system containing 5 wt % of the nanoparticles showed the highest reduction of the fluid flow rate. Scanning electron microscopy and probability density function tests of the best material allowed inferring that composite prepared by magnetic induction presents a non‐Gaussian distribution of the diameter, which is directly related to the observed sealing effect. These results showed that proposed polymer/polymerization system can be very useful to the sealing applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45549.     

Triethanolamine–azodiisobutyronitrile mixture as a foaming agent for low‐density unsaturated polyester resin manufacturing at a low temperature

A triethanolamine (TEA)–azodiisobutyronitrile (AIBN) mixture was applied to the manufacturing of a low‐density unsaturated polyester resin (LDUPR) at a low temperature ranging from 53 to 66 °C. Hydrogen‐bonding activation in the TEA–AIBN mixture was put forward, and this agreed with the NMR and Fourier transform infrared (FTIR) spectroscopy results. A heat balance in the curing process of a vinyl ester unsaturated polyester resin (UPR) was examined and characterized by differential scanning calorimetry, FTIR spectroscopy, and scanning electron microscopy. The TEA–AIBN mixture decomposed easily because of the hydrogen‐bonding action between TEA and AIBN. The heat release of the activated AIBN decomposition led to the early endothermic polymerization of the vinyl ester UPR. Hydrogen‐bonding activation followed by the heat‐balance process enabled us to manufacture the LDUPR at low temperature. The optimal parameters of LDUPR manufacturing, including a ratio of TEA to AIBN of 0.4 and a dosage of TEA–AIBN mixture of 2.5 phr at a curing temperature of 60 ± 1 °C, were defined by the testing of the apparent density (ρ) and compressive strength of LDUPR. Under these conditions, ρ was 0.39 ± 0.01 g/cm³, and the specific compressive strength was 33.92 ± 1.31 MPa g^?1 cm^?3. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44797.     

Aging of anhydride‐hardened epoxies in lubricants at elevated temperatures

In automotive under‐the‐hood applications, electronics respectively their packaging materials come in contact with automotive fluids. The effect of automatic transmission fluid (ATF) on an anhydride‐cured epoxy was investigated at temperatures up to 180 °C for up to 1000 h. This study has shown that ATF retards the oxidative aging of the epoxy, presumably due to oxygen consumption. Whereas in air the material underwent a thermo‐oxidative aging with a mass loss of up to 4% and a strong broadening of T_g to higher temperatures, in ATF a temperature dependent distinctive drop of T_g from 142 to 126 °C after 1000 h aging at 180 °C, and a mass loss of maximum 1% was observed which might be a thermal decomposition of the epoxy material. A slight broadening of the damping factors might indicate an intrusion of ATF components. A color change of the samples could be observed after aging in air and ATF, with the discoloration in air being more intense. An explanation for the color change might be either a minor amount of oxygen causing an oxidative discoloration reaction or the intrusion of colored ATF degradation products. While the oxidation‐kinetics in air exhibited Arrhenius temperature‐dependence the mechanism in ATF changed above 165 °C. An acceleration of aging tests at temperatures beyond 150 °C is, therefore, not possible. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44877.     

Thermosetting polymers from cationic copolymerization of tung oil: Synthesis and characterization

The cationic copolymerization of tung oil with the divinylbenzene comonomer initiated by boron trifluoride diethyl etherate produces promising plastics. The gel times are largely dependent on the relative composition and the reaction conditions and vary from a few seconds to 1 h. Controlled reactions producing homogeneous materials can be obtained by (1) lowering the reaction temperature or (2) decreasing the initiator concentration to less than 1 wt % or (3) adding a certain amount of a less reactive oil, such as soybean oil, low saturation soybean oil (LoSatSoy), or conjugated LoSatSoy to the reaction. The resulting polymers are rigid and dark brown in color. The weight % of the starting materials converted to the crosslinked polymer is ∼85–98% as determined by Soxhlet extraction with methylene chloride. The structure of the bulk product is that of a crosslinked polymer network plasticized by a small amount of low molecular weight oil. The chemical composition of the bulk polymers varies with the original composition of the tung oil system. Dynamic mechanical analysis shows that the resulting products are typical thermosetting polymers with densely crosslinked structures. The modulus of the plastics is approximately 2.0 × 10⁹ Pa at room temperature. One broad glass transition is observed at approximately 100°C. Thermogravimetric analysis shows that the tung oil polymers are thermally stable below 200°C with a 10% weight loss in air around 430°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1044–1056, 2000     

Synthesis of phenetidine-based telechelics and subsequent reactions with water-based curing reagents

The development of soluble telechelics based on aniline are highly desirable due to numerous applications that are possible, especially in the coatings and adhesive industry. Control of molecular length and ease of synthesis lends o-ethoxyaniline to be an ideal candidate for the synthesis of amino-terminated telechelic oligomers. Combined with the higher solubility and reactivity, curing of these functionally reactive oligomers has been accomplished using aqueous formaldehyde, as well as water-dispersed epoxy resins. Spectroscopic studies have been done to characterize the prepolymers, as well as the cured materials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1811–1817, 1998     

Synthesis and characterization of 2‐oxazoline‐benzoxazine compound and its polymer

A novel 2‐oxazoline‐benzoxazine (POB) was synthesized with 2‐(hydroxylphenyl)‐2‐oxazoline, 1,3,5‐triphenylhexahydro‐1,3,5‐triazine and paraformaldehyde. The chemical structure of the monomer was confirmed by FTIR, ¹H‐NMR, ¹³C‐NMR, and MS. The curing behavior of the monomer was studied by DSC and FTIR, and the ring opening reaction of the monomer was found to occur from 187.5°C. The results of DMA and TGA demonstrated that the thermal properties of polymer for POB monomer (P‐m) are better than polymer for POB precursor (P‐p), because that the oligomer in benzoxazine precursor decreased the perfection of the polymer's network structure; it was also found that the thermal properties of P‐m and P‐p are much better than the common polybenzoxazine and the composite material of benzoxazine and 2‐oxazoline. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci , 2008.     

Synthesis of epoxy‐functionalized hyperbranched poly(phenylene oxide) and its modification of cyanate ester resin

High curing temperature is the key drawback of present heat resistant thermosetting resins. A novel epoxy‐functionalized hyperbranched poly(phenylene oxide), coded as eHBPPO, was synthesized, and used to modify 2,2′‐bis (4‐cyanatophenyl) isopropylidene (CE). Compared with CE, CE/eHBPPO system has significantly decreased curing temperature owing to the different curing mechanism. Based on this results, cured CE/eHBPPO resins without postcuring process, and cured CE resin postcured at 230°C were prepared, their dynamic mechanical and dielectric properties were systematically investigated. Results show that cured CE/eHBPPO resins not only have excellent stability in dielectric properties over a wide frequency range (1–10⁹Hz), but also show attractively lower dielectric constant and loss than CE resin. In addition, cured CE/eHBPPO resins also have high glass transition temperature and storage moduli in glassy state. These attractive integrated performance of CE/eHBPPO suggest a new method to develop high performance resins. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of TiO2 epoxy nanocomposites by ultrasonic dispersion and resulting properties

Nanocomposites gained more and more importance in the last few years because of their improved performance over the neat polymer matrix, that is, toughness and stiffness can be enhanced simultaneously by the addition of nanoparticles. However, the dispersion of these particles in the matrix remains a big challenge. In this study, two types of TiO₂ nanoparticles were dispersed in two different epoxy resins by means of ultrasound. The particle size development in dependence on the dispersion time was investigated by dynamic light scattering for the different material systems. Furthermore, the influence of the viscosity on the sonication process' efficiency was analyzed. The resulting nanocomposites were tested for fracture and Charpy toughness. SEM images revealed that the improved fracture toughness properties are correlated to a rougher fracture surface, whose formation dissipates more energy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012