Morphology of polyphosphazenes: Oriented and unoriented

Abstract

The purpose of this work is to obtain a better understanding of the morphology of polyphosphazenes and to establish some general morphological characteristics. Solution cast, stretched and annealed films of poly(bistrifluoroethoxyphosphazene), PBFP, and poly(bisphenoxyphosphazene), PBPP, have been investigated by electron and optical microscopy. Thin and thick films were prepared using different solvents. Films were cast and stretched below as well as above T(1), the thermotropic transition of each polymer. In the case of PBFP its T(1) transition was established through birefringent-temperature measurements and orientational changes were measured as a result of heat cycling stepwise through T(1). Thin specimens were oriented on electron microscope grids using a mechanical stretcher; thicker films were drawn by hand at various temperatures, too. Orientation was effectively induced through casting on hot liquid surfaces at temperatures > T(1). PBPP exhibits a layer (domain) morphology of high crystallinity and orientation under these conditions. Dislocations or stacking faults can be recorded in darkfield in PBPP but the low stability of PBFP to the electron beam does not permit dark-field images to be recorded. Optical microscopy was used to record cast film textures.

High temperature behavior of poly[bis(2,2,2-trifluoroethoxy)phosphazene]

“…Some of these morphologies can be mistaken as spherulitic unless they are examined properly in the optical microscope. This behavior has already been associated with sub-microscopic structural and birefringence changes reported elsewhere 4,8) , regardless of the polymer molecular weight. The birefringence of each sample disappears upon heating through their respective T m 's (isotropization temperatures) where the melts appear to be isotropic and optically homogeneous phases 2,4) under crossed polars in the optical microscope.…”

Influence of the length of side substituents on optical and electro-optical properties of polydialkoxyphosphazenes

“…A variation in the spatial shape of the monomer unit and a change in its sign of anisotropy with length ening of aliphatic side groups may be responsible for the phase behavior and morphological properties of a number of PDAOPs at m = 4-6 [4][5][6][7]. As was men tioned above, the shape of the monomer unit of PDAOP is characterized by the highest symmetry in the "critical" region of side chain lengths.…”

“…Once S is determined, Δа may be For this purpose, let us use the results of the quan tum chemical simulation obtained for the analogs of the monomer unit of PDAOP samples to determine the value of ( /M 0 ) entering Eq. (6).…”

“…As was men tioned above, the shape of the monomer unit of PDAOP is characterized by the highest symmetry in the "critical" region of side chain lengths. Shape sym metry, which provides competitive opportunities for molecule packaging, may cause various kinds of rear rangements during sequential heating and cooling of polydihexoxyphosphazene and polydiheptoxyphosp hazene [4][5][6][7]. Moreover, the possibility of the alterna tive orientation of highly symmetric PDAOP chains in terms of the shape of their units in a melt may be responsible for the mesomorphic behavior of these polymers only in a certain side chain length range.…”

“…Studies devoted to polydialkyloxyphosphazenes (PDAOPs) (R = -O-(CH 2 ) х -CH 3 ) indicate that their physical properties are dependent on the lengths of side substit uents [1,3,[4][5][6][7]. Some properties change monotoni cally with side chain lengthening, whereas the other properties remain unaffected.…”