Synthesis, Characterization And Properties Of High Performance Cyanate Ester Resins

Cyanate ester (CE) resins are a family of new generation thermosetting resins whose performance characteristics make them direct competitors for standard epoxy resins and bismaleimides in high performance applications. The CE resins are gifted with many attractive thermal, electrical, water resistance and epoxy-like processing properties required of an ideal matrix resin, bridging the gap in thermal performance between engineering Epoxy and bismaleimides. CE resins are widely used in printed circuit boards (PCBs), low-dielectric antennas and radar, aerospace structural composites.In the recent years, the demand for high performance CE resins has increased tremendously due to the rapid development of PCBs and aerospace industries. Development of CE resins with enhancing glass transition temperatures (Tg), low dielectric constant and dissipation, water resistance and flame retardance are highly expected.By taking advantage of the molecular design flexibility of cyanate ester monomers, a series of novel CE resins with excellent dielectric performance and water resistance were synthesized through the incorporation of various functional groups in the backbone and ortho-alkylation in the cyanate group. Non-halogen flame retardant CE resins were developed by the incorporation of thermal-resistance group in the backbone. Moreover, novel nonfunctional cyanate ester monomer was prepared by the cyanation of cashew nut shell oil (CNSL). The main works and conclusions were listed as following:1. Phenol precursor BBZ was obtained by the reaction of 2,6- dimethylphenol with 1, 4-bis (methoxymethyl) benzene in the presence of p-toluenesulfonic acid (PTS) as catalyst. The corresponding dicyanate BBZCy was prepared through the reaction of BBZ precursor with cyanogen chloride. The chemical structures were characterized by FTIR,1H NMR, EI-MS and EA. Thermal cure reaction of BBZCy was monitored by DSC and in situ FTIR. The cure kinetics was studied by nonisothermal DSC and kinetics parameters were determined by Kissinger method and Crane equation. The conversion of cyanate group versus time at different cure temperature was evaluated by in situ FTIR. The properties of CE resin were evaluated. The results showed that cured BBZCy resin exhibited good thermal properties with glass transition (Tg) was 219?and thermal stability with 5% weight-loss temperature at 427?and 35% char yield at 800?. The BBZCy resin exhibited a lower dielectric constant (2.66 at 1GHz), a lower dissipation factor (0.0054 at 1GHz), lower water absorption (0.8% at 1 OOh) than the commercial bisphenol A cyanate ester resin.2. Phenol precursors BBP and BHBZ were obtained by the reaction of phenol with 4, 4'-bismethoxymethylbiphenyl and 1,4-bis (methoxymethyl) benzene, respectively. The corresponding dicyanates BBPCy and BHBZCy were prepared through the reaction of phenol precursors with cyanogen chloride. The chemical structures were characterized by FTIR,1H NMR, EI-MS and EA. Thermal cure reaction of BBPCy and BHBZCy were monitored by DSC and FTIR. The thermal properties of CE resins were evaluated by DMA and TGA. The flame retardance of BBPCy and BHBZCy resins were evaluated by UL-94 and LOI test. The results showed that BBPCy and BHBZCy resins showed excellent thermal stability and flame retardant properties due to the incorporation of aromatic 4,4'-biphenylene moiety and p-xylene moiety. Moreover, BBPCy and BHBZCy resins exhibited good dielectric properties, water resistance and mechanical properties. Both cyanate ester resins exhibited excellent flame retardancy.3. Oligomeric phenol precursors containing diphenyl ether (DPEPh) and dimethylbenzene (DBMPh) were prepared by the reaction with phenol with diphenyl ether terminated with methoxyl group and dimethylbenzene terminated with methoxyl group, respectively. The corresponding cyanate monomers (DPEPCN) and (DMBPCN) were prepared by the reaction of phenol precursors with cyanogen chloride. The chemical structures were characterized by FTIR and EI-MS. The molecular weight of phenol precursors were obtained by gel permeation chromatography (GPC). Thermal cure reaction was monitored by DSC and FTIR. The properties of CE resins were evaluated. The results show that DPEPCN and DMBPCN resins exhibited lower Tg that that of bisphenol A cyanate ester resin whereas they owned their characteristics:Thermal stability and water resistance properties for DPEPCN resin and good dielectric and water resistance properties for DMBPCN. In addition, viscosity of DPEPCN and DBMPCN at 80?is lower than 400mPa.s, which can be used in various processings of CE resins.4. Monofunctional group CE monomer (CNSLCy) and dicyanate (DCPDCN) were synthesized through the reaction of CNSL extracted from cashew nut shell and phenol precursor containing dicyclopentadiene with cyanogen chloride, respectively. The chemical structures were characterized by Fourier-transform infrared (FTIR) spectroscopy,1H nuclear magnetic resonance (1H NMR), mass spectroscopy (EI-MS or GC-MS) and elemental analysis (EA). DCPDCN and bispheno A cyanate ester resin (BADCy) were modified by CNSLCy. The results showed that thermostable properties and flexural modulus of CE resins modified by CNSLCy decreased with the content of CNSLCy accordingly whereas the dielectric properties and water resistance of CE resins modified by CNSLCy were enhanced a lot.