Abstract
Introducing multiphase structures into benzoxazine (BOZ)/epoxy resins (ER) blends via reaction-induced phase separation has proved to be promising strategy for improving their toughness. However, due to the limited contrast between two phases, little information is known about the phase morphological evolutions, a fundamental but vital issue to rational design and preparation of blends with different phase morphologies in a controllable manner. Here we addressed this problem by amplifying the difference of polymerization activity (PA) between BOZ and ER by synthesizing a low reactive phenol-3,3-diethyl-4,4′-diaminodiphenyl methane based benzoxazine (MOEA-BOZ) monomer. Results indicated that the PA of ER was higher than that of BOZ. The use of less reactive MOEA-BOZs significantly enlarged their PA difference with ER, and thus increased the extent of phase separation and improved the phase contrast. Phase morphologies varied with the content of ER. As for the phase morphological evolution, a rapid phase separation could occur in the initial homogeneous blends with the polymerization of ER, and the phase morphology gradually evolved with the increase in ER conversion until the ER was used up. The polymerization of ER is not only the driving-force for the phase separation, but also the main factor influencing the phase morphologies.
Highlights
Due to the good processability, excellent thermal and mechanical properties, thermosetting resin (TS) has been widely used in the coating, electrical, and aerospace fields [1,2,3,4,5].TS resins are brittle materials that show insufficient toughness and elongation at break, which limits their use as structural materials
We proposed a phase separation mechanism for the MOEA-BOZ/DGEBA-ER/IMZ blends based on the morphological evolutions and corresponding residual curing exothermic curves after curing at different stages obtained by differential scanning calorimetry (DSC)
We synthesized a novel MOEA-BOZ monomer with two ethyl groups modified on the phenyl rings of traditional MDA-BOZ resin
Summary
Due to the good processability, excellent thermal and mechanical properties, thermosetting resin (TS) has been widely used in the coating, electrical, and aerospace fields [1,2,3,4,5].TS resins are brittle materials that show insufficient toughness and elongation at break, which limits their use as structural materials. Among the various toughening methods, reaction-induced phase separation, which was designed as the uniform precursor system undergoing a phase separation into a multiphase structure during the development of the curing process, was the most effective one [6,7]. This method could significantly improve the toughness of TS resin without sacrificing its high modulus, glass transition temperatures (Tg ), and excellent thermomechanical properties, which has been widely reported in high performance engineering thermoplastic (TP) (i.e., polyimide, poly(ether imide), and poly(ether sulphone)) modified TS systems [8,9,10,11,12]. The development of advanced TS resin systems with low viscosity and high performance, especially excellent toughness, is still challenging and a new modification strategy is needed
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