Rheological properties and phase state of copolyphosphazenes

Effects of the side 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptoxy groups in poly(bis-trifluoroethoxy-phosphazene) on the Theological properties and phase state of copolyphosphazenes were studied by the capillary viscometry and DSC techniques. The content of CH2(CF2)6H groups in the copolymers was varied from 0.5 to 100 mol %. The rheological properties of the samples depended on their phase state (isotropic or mesophase) having a concentration-dependent temperature interval of existence. The rheological behavior of copolyphosphazenes in the isotropic state resembles that of typical flexible-chain polymers, including the phenomenon of spurt (the loss of contact between the melt and the surface of the measuring device at a high shear rate). The spurt stress in copolyphosphazenes is markedly lower than that in carbochain polymers. The rheological properties of copolyphosphazenes in the mesophase state are quite different, showing evidence of the yield point followed by pseudoplastic behavior of the melt. The series of copolymers studied offers a convenient model system whose rheological behavior can be varied from pseudoplastic to viscoplastic by slightly changing the chemical composition of samples or temperature. © 1998 by Borisenkova. Vasil'ev, Kulichikhin. Kuptsov, Tur.