A thermosetting resin system, based on tetraglycidyl-4,4′-diaminodiphenylmethane, has been developed via copolymerization with 4,4′-diaminodiphenylsulfone in the presence of a newly synthesized liquid crystalline epoxy (LCE). The curing behavior of LCE-containing resin system was evaluated using curing kinetics method and Fourier transform infrared spectroscopy. The effect of LCE on the thermal and mechanical properties of modified epoxy systems was studied. Thermogravimetric analysis indicated that the modified resin systems displayed a high T_0.05 and char yield at lower concentrations of LCE (≤5 wt%), suggesting an improved thermal stability. As determined using dynamic mechanical analysis and differential scanning calorimetry, the glass transition value increased by 9.7% compared to that of the neat resin when the LCE content was 5 wt%. Meanwhile, the addition of 5 wt% of LCE maximized the toughness with a 175% increase in impact strength. The analysis of fracture surfaces revealed a possible effect of LCE as a toughener and showed no phase separation in the modified resin system, which was also confirmed by dynamic mechanical analysis. © 2016 Society of Chemical Industry

A thermosetting resin system, bismaleimide (BMI) modified allyl novolac (BAN), was developed via reactive blending of formaldehyde and catalyst drop wise to improve the extent of reaction between BMI and phenol-carbenium ions. For improving the curing behavior and mechanical properties, dicumyl peroxide (DCP) was selected as a novel curing initiator to compare with hexamethylenetetramine (HTMA) which is the most common curing initiator used in the manufacture of phenolic resins. BAN was characterized by ¹H nuclear magnetic resonance and Fourier transfer infrared spectroscopy. Curing behavior with initiators was analyzed by differential scanning calorimetry and glass transition temperature of the cured resins was examined by dynamic mechanical analysis. For evaluating efficiency of the modified system, composite samples using polyvinyl acetyl fiber were molded and tested for flexural properties before and after ageing at 150°C for 1,000 h. The morphology of composite samples was examined by scanning electron microscope, and the effects of the incorporated initiators on the mechanical and thermal properties of composite were investigated. The results indicated that the initiators reduced the curing temperature effectively and improved the curing process. DCP proved to be more effective in crosslinking and heat resistance than HTMA. Meanwhile, the molded composite with DCP showed higher mechanical properties before and after ageing when compared with HTMA curing initiator. Therefore, DCP/BAN resin system with good heat resistance, higher mechanical properties, and better process ability can be applied as matrix resin for the manufacturing of advanced fiber reinforced composites. POLYM. COMPOS., 37:2260–2271, 2016. © 2015 Society of Plastics Engineers

A new hyperbranched polymer (HBP) with a flexible aromatic skeleton and terminal epoxy groups was synthesized to improve the toughness of diglycidyl ether of bisphenol A. The HBP was characterized using nuclear magnetic resonance, Fourier transfer infrared spectroscopy and gel permeation chromatography. The effect of HBP on the thermomechanical and mechanical properties of modified epoxy systems was studied. For evaluating the efficiency of the modified epoxy systems, composite samples using glass fiber cloth were molded and tested. Using dynamic mechanical analysis, a slight reduction in glass transition temperature (T_g) with increasing HBP content was observed. Analysis of fracture surfaces revealed a possible effect of HBP as a toughener and showed no phase separation in the modified resin systems. The results showed that the addition of 15 phr HBP maximized the toughness of the modified resin systems with 215 and 40% increases in impact and flexural strengths, respectively. T_g and heat resistance of cured modified resin systems decreased slightly with an increase in HBP content and, at 15 phr HBP, only a 2.6% decrease in thermomechanical properties was observed. Meanwhile, a molded composite with HBP showed improved mechanical properties and retention rate at 150 °C as compared to that made with neat resin. © 2015 Society of Chemical Industry

For reducing the cure temperature and improving the thermal stability and mechanical properties, a thermosetting resin system composed of novolak and bismaleimide (BMI) was developed by reactive blending and using dicumyl peroxide (DCP) as a novel curing agent. Novolak was allylated and reacted with BMI to produce bismaleimide allylated novolak (BAN), and the effect of DCP on flexural, impact and heat distortion temperature of cured resin were investigated. On the basis of improved mechanical and thermal properties at 0.5% DCP contents, the curing behavior of DCP/BAN resin system was evaluated by DSC analysis. Ene, Diels-Alder, homo-polymerization and alternating copolymerization which occurred in DCP/BAN resin system were further verified using FTIR at sequential cure conditions from 140 to 200°C. Kissinger and Ozawa-Flynn-wall methods were used to optimize the process and curing reactions of DCP/BAN resin system. The results showed that the addition of 0.5% DCP in BAN reduced the curing temperature and time of the modified resin. For evaluating process ability of the modified system, composite samples using polyvinyl acetyl fiber were molded and tested for flexural properties. The resulting samples showed better flexural properties when compared with the composite made with neat BAN. The modified 0.5% DCP/BAN resin system with good mechanical properties and manufacturability can be used for making bulk molding compounds and fiber reinforced composites required in various commercial and aerospace applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41829.