Effect of monomer chemical structures on the cell structures and properties of cyanate ester foams

Cyanate ester (CE) foams with different chemical structures were prepared using bisphenol A dicyanate ester (BADCy), bisphenol E dicyanate ester (BECy), and tetramethyl bisphenol F dicyanate ester (TBFDCy) as monomers, through a two-step process. Rheological tests were performed to investigate the optimal conditions for the preparation of these foams. The results of morphology by scanning electron microscopy showed that cells are in the form of nearly spherical shape in foams from TBFDCy and BADCy and oval in foam from BECy. The thermal properties of the three CE foams were studied by methods of dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetry/differential thermogravimetry analysis. The glass transition temperature (T-g) obtained from DMA tests are 274, 264, and 241 degrees C for the foams from TBFDCy, BADCy, and BECy, respectively, which are apparently higher than that tested by DSC method. The T-g, compressive properties, and thermal stabilities of the foams are improved after the introduction of the alkyl-substituent groups to the same aromatic ring of -OCN functionality, and the chemical structure-properties relationships are explained according to the monomer chemical structures.