The plateaumodulus of polyphenylquinoxaline (PPQ-E) films has been obtained byfromtheir dynmic mechanical properties curves．Using these data

the entanglement density of PPQ-E films

2.37×1026m-30．39mmol／cm3

has been estimated．The deformation mechanism of polyphenylquinoxaline (crazing mechanism．or shear yielding mechanksm

or both)

can be predicted according to entang-lement density values. The changes in morphdogy of PPQ-E films during tensile ddormation have been observed by Pohrized Light Microscope．The resultshows that crazing first appears in the tensile process

then shear yidding appears．It neois to point out the craze is terminated by micro-shear band andthe diection of araze in shear band is also changed

which prevents the crazegrowth into crack and avoid the failure of material This result is inaceordance with the theprediction on the basis of the entangleneat density data The morphology and structure of crazes in PPQ-E thin film have been determined by TEM．The craze morphology of PPQ-E is mainly fibril craze consisting of micro-fibrils and micro-voids

the interface between bulk and craze is distinct．Multiply crazes

blunting of craze tip and shear deformation zone are also observed. This result reflects the accordance of entanglement density and the morphology and structure of crazes.