Synthesis And Modification Of High Performance Cyanate Ester Resins

Cyanate ester resins(CE)area class of thermosetting resinsfeaturing excellent electrical,thermal,mechanical and flame-retardant properties.Thus,CE resins have been widely used in the aerospace and electronic industries.However,CE resins still suffer high curing temperatures and relatively low toughness.Consequently,research efforts have been directed towards the development of novel CE monomers,and the modification of existing CE resins with other thermosetting or thermoplastic polymers.The processability and toughness were improved through these modifications,usually at the cost of decreased thermal or dielectric properties.In this dissertation,we first present the modification of the benchmark CE resin(e.g.BADCy)with highly soluble and thermally resistant thermoplastic polyimides;then two cyanate ester monomerswith rigid but non-coplanar or contorted moieties were developed,and their processability,and the thermal,mechanical,and dielectric properties of cured resins were systematically investigated.The major findings are as follows:1.A thermoplastic polyimide resin(TPI)with high T_g(360?)and solubility(>20%in BADCy)was prepared by using 3,4'-BPDA,4,4'-ODA and TFMBas monomers.The good solubility of TPI in BADCy rendered the solventless preparation of BADCy/TPI blends.The curing behavior of BADCy/TPI blends was analyzed by FTIR,DSC,and rheological measurements.The mechanical properties of the cured resins were characterized using universal testing machine,DMA,TGA,and dielectric measurements.With the increase of TPI contents,the peak values of curing exotherm decreased from 324to 273oC,and the gelation time at 200oC decreased to 11 minutes.When the TPI content was greater than10%,the resultant semi-IPN displayed phase-separated morphologies.Compared with pure polycyanurate,semi-IPNs showed improved mechanical properties.The impact strength of semi IPN was 47-320%higher than that of pure polycyanurate.The glass transition temperatures of semi-IPN were in the range of 308-312oC.The addition of TPI also improved the dielectric properties of semi-IPN.With the increase of TPI contents,the dielectric constant and dielectric loss factor decreased gradually.2.By diazotization of 2,2'-bis(trifluoromethyl)-4,4'-benzidineand subsequent electrophilic substitution with water,2,2'-bis(trifluoromethyl)-4,4'-dihydroxybiphenyls were prepared.After cyanation,4,4'-biscyanato-2,2'-trifluoromethylbiphenyl(TFMBDCy)wassynthesized.The structure of TFMBDCy was characterized by FTIR,NMR and X-ray single crystal diffractometer.The curing behavior of TFMBDCy was studied by using DSC and rheometer.The thermal and mechanical properties of TFMBDCy network were studied by TGA,DMA,and universal testing machine.The T_g value of TFMBDCy network is 372oC,which is much higher than that of BADCynetwork(310oC).Moreover,its compressive strength is 203 MPa,31%higher than that of BADCy network.TMFBDCy network also displayed improved dielectric properties and reduced water uptake relative to BADCy network.3.5,5'-Dicyanato-3,3,3',3'-tetramethyl-2,2',3,3'-tetrahydro-1,1'-spirobi[indene](SBIDCy)was prepared through the cyanation of its bisphenol precursor,andits structure was determined by FTIR and NMR.The curing behavior of the monomer and its blends with BECy was studied using DSC and rheometer,and the thermal properties,mechanical properties,and dielectric properties of the cured resins were characterized with TGA,DMA,universal testing machine,and impedance analyzer.The results show that the T_g value of SBIDCy network was 354oC,much higher than that of BECy network.Furthermore and its dielectric and mechanical properties were improved compared BECy network.