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The thermal transition behavior of polyorganophosphazenes
Author(s) -
Schneider N. S.,
Desper C. R.,
Singler R. E.
Publication year - 1976
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1976.070201114
Subject(s) - materials science , thermal , transition (genetics) , polymer science , chemistry , thermodynamics , physics , biochemistry , gene
The thermal transition behavior of poly[bis(trifluoroethoxyphosphazene)] (I) and two samples of poly[bis( p ‐chlorophenoxyphosphazene)] (II) have been studied as representative alkoxy‐ and aryloxy‐substituted polyorganophosphazenes. Several of the polymers of this class are reported to exhibit two first‐order transitions, denoted herein as T (1) for the transition from a crystalline to mesomorphic state and T m for the true melt. Studies of these two polymers were undertaken to gain a further understanding of this behavior. Optical microscopy on a solution‐cast film of I showed that the details of spherulitic morphology persist through T (1) = 90°C and remain undisturbed through the temperature interval up to T m = 240°C. The study of II by x‐ray diffraction reveals that two sharp lines are observed above T (1) = 165°C and that orientation is not randomized upon heating to temperatures as high as 238°C. Considerable improvement in the crystalline diffraction pattern results from the thermal treatment. A detailed examination was also made by differential scanning calorimetry (DSC) of the effects of cycling through T (1), annealing in the temperature interval between T (1) and T m and for I, the influence of controlled crystallization from the melt. The results indicate that the organization in the mesomorphic state, as influenced by thermal history, has a profound affect on the peak position, area, and sharpness of the endotherm at T (1). For I, the apparent heat of fusion at T (1) is about ten times greater than at T m , whereas for II, no DSC peak is observed at T m = 365°C, suggesting that the ratio of the heats of fusion at T (1) and T m is greater than 50. However, estimated volume changes at the two transitions are nearly equal. These results are compared with those of other polymers which exhibit an intermediate state of order and with molecular liquid crystals.