POLYMORPHISM OF POLY[BIS(4-ISOPROPYLPHENO XY)PHOSPHAZENE]

Polymorphism of oly[bis(4-isopropylphenoxy)phosphazene]-PB(4-Ip)PP has been investigated by DSC, X-ray diffraction measurements and electron microscopy. Orthorhombic (alpha-form) and monoclinic (beta-form) of t hree-dimensional crystalline forms and two-dimensional pseudo-hexagona l mesophase (delta-form) are found depending upon the thermal history of specimens. The unit cell dimensions of the alpha-form and the beta- form are estimated as a = 3.14 nm, b = 1.14 nm, c = 0.992 nm and a = 2 .45 nm, b = 1.94 nm, c = 1.12 nm, gamma = 101.5 degrees, respectively. The intermolecular distance in the mesophase is evaluated to be 1.64 nm. DSC measurements for the original PB(4-Ip)PP him exhibit the alpha -->beta and beta-->delta transitions at 86 degrees C and 120 degrees C , respectively. Whenever the delta-form PB(4-Ip)PP is cooled from the mesophase, it transforms into the alpha, beta, or alpha+beta forms dep ending upon the cooling rates. When the alpha-form specimen obtained b y cooling from the mesophase is heated, the alpha-form transforms into the beta at 83 degrees C, the beta-->delta transition occurs partiall y at 107 degrees C and the delta-form is established completely at 137 degrees C after the following heating. On the other hand, the beta-fo rm resulted from the mesophase transforms into the delta-form sharply at 135 degrees C.