Novel Microcapsule Modified Cyanate Ester Resin

Cyanate ester (CE) resin is a kind of novel high-performance thermosetting resins, which contains two or more isocyanate functional groups(—OCN). Since its appearence in the late 70s of 20th century, its unique structure has attracted wide attention of people. Structural features supply outstanding integrat properties for CE resin, such as excellent electrical insulation properties, low moisture absorption, high thermostability, excellent dimensional stability, good mechanical properties and so on, and thus it has a wide range of applications in the electronics, aerospace, electrical insulation, coatings, adhesives, optical instruments, medical equipment and many other fields. However, due to a large number of aromatic rings in the crosslinked structure and high crosslinking density, cured CE resin is brittle. Toughening has been an important topic in the researches on CE resin.Many domestic and foreign researchers have carried out studies on toughening of CE resin, and developed many methods. The main toughening methods include blending with thermoplastic polymers, thermosetting resins, or rubber elastomers etc. Recently, microcapsule - toughening becomes a novel method of thermosetting resins. Microcapsule is a tiny particle containing liquid, solid or gas, its special structure gives it unique versatility. Toughening CE resin by using microcapsules can not only improve the mechanical properties of the resin, but also gives versatility for the resin. The aim of this thesis is to synthesize a new type of microcapsules, which are then used to toughening CE resin. The main contents of this thesis include:With bisphenol A di-isocyanate resin (BADCy) and bisphenol A type epoxy resin (DGEBPA) as raw materials, imidazole as catalyst, a new kind of microcapsules, cyanate ester/epoxy polymer microspheres (MS), were prepared via a emulsion polymerization. And then, a new series of poly(urea-formaldehyde) microcapsules (PUMC) were prepared by in situ polymerization with urea and formaldehyde as wall materials and obtained MS as core material. The effect of different processing parameters on the physical properties, chemical structure and thermal properties of MS were discussed, such as different weight ratios between CE and epoxy resin, different imidazole content and so on. The chemical structures of MS and PUMC were analyzed with Fourier transform infrared spectroscopy (FTIR). The appearances of MS and PUMC were observed by optical microscopy (OM), and scanning electron microscopy (SEM), and the internal structure of MS and PUMC were surveyed by laser scanning confocal microscope (LCSM) and SEM. The particle size and distribution of MS was used OM techniques to determine. The thermal properties of MS and PUMC were investigated using differential scanning calorimetry (DSC) and thermal gravity analysis (TGA). Results show that PUMC can be successfully synthesized with the above two-step method, and the size and surface morphology of MS can be controled by adjusting the various process parameters. The MS and PUMC synthesized have good storage stability and thermostability.PUMC was added to BADCy resin to prepare BADCy/PUMC resin system, and the effect of PUMC on the reactivity and mechanical properties was discussed. The cross-section morphology of the resin system was observed by SEM, and the toughening mechanism of PUMC on BADCy resin was analyzed. Results indicate that with the increase of PUMC content, the gel time of BADCy decreases, however, the effect becomes pronounced at lower temperatures, which weakens at higher temperatures. The appropriate loading of PUMC can enhance the mechanical properties and hot-water resistance of BADCy resin, while slightly decrease the initial decomposition temperature and glass transition temperature of the resin, however which has little effect on the dielectric properties.