ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Poly(dimethylphosphazene) crystals have been grown by two techniques, namely: (a) dilute-solution crystallization and (b) from the supercooled melt. An orthorhombic crystal form with a = 1,390 nm, b = 0,598 nm and c = 0,473 nm was deduced from electron and X-ray diffraction. There are four monomers per unit cell of density 1,267 g/cm3. Streaks connecting the (hk0) reflections in electron diffraction are suggestive of lattice defects along the [b] axis. Whenever crystals are annealed just below Tm where sufficient mobility exists, the “streaks” are absent when the specimen is cooled to room temperature. Differential scanning calorimetry (heating) exhibits two endothermic peaks at 142°C and 146°C, corresponding to T(1) and Tm transitions, respectively. A mesophase exists between these closely spaced peaks. A wider mesophase range is encountered in poly(oxyphosphazenes).
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1992.021931102
