Structure and polymorphic behavior of poly(dipropylphosphazene)

X-ray diffraction and DSC investigations indicate that poly(dipropylphospha zene) is characterized by one ordered crystalline modification and a thermo tropic mesophase, which is formed at temperatures higher than 248 degrees C and appears to maintain a 2D order. The structure of the crystalline phase has been determined. the unit cell is monoclinic, space group P2(1)/c, and the cell parameters are: a = 9.10(5) Angstrom, b = 4.88(4) Angstrom, c = 1 9.05(10) Angstrom, beta = 92.43(1)degrees. The refinement indicates a twofo ld helical conformation with a nearly planar (CT)(2) backbone. The cyclic t rimer was studied by DSC and single crystal X-ray diffraction: the unit cel l is monoclinic, space group P2/c, cell parameters are 10.0131(5) Angstrom, b = 7.8342(4) Angstrom, c = 15.1782(11) Angstrom, beta = 95.844(7)degrees The conformations of the side chains in the polymer and the trimer are clos ely related, as already found in polydiethylphosphazene. In the polymer, ho wever, the side chains probably show some disorder yet to be characterized. (C) 1999 Elsevier Science Ltd. All rights reserved.