A series of poly(aryloxyphosphazene)s was prepared with phenoxy and p‐ethylphenoxy substituents in various ratios. The thermal, morphological, and rheological properties of this series of polymers were studied by differential thermal analysis, x‐ray analysis, and rheometrics mechanical spectroscopy. Thermal analysis showed that the resulting polymers follow melting‐point‐depression‐ and glass‐transition‐temperature‐composition relationships expected of random copolymers. The lower first‐order transition temperature [T(1)] disappears near equimolar substitution while the higher first‐order transition temperature (Tm) persists over the whole range of compositions. X‐ray analysis revealed that crystalline order in the polymer chain direction is destroyed by nearly equimolar substitution but lateral order remains. The rheological characterization of a copolymer with nearly equimolar substitution showed that the polymer is in a pseudocrosslinked state indicating the existence of chain‐to‐chain interactions. When a small amount of an antioxidant (6‐dodecyl‐1,2‐dihydro‐2,2,4‐trimethylquinoline) is added, the lateral order of the copolymer is destroyed, and its rubbery plateau modulus decreases by several fold.

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A series of phosphonitrilic fluoroelastomers which have excellent solvent resistance and low temperature flexibility, and which perform well under a broad range of service conditions, have been developed. The solution properties of one of these polymers were studied more extensively in order to develop suitable quality control procedures and to gain a better understanding of the polymer structure. Solvents for these procedures were established, fractionation procedures were developed, and intrinsic viscosity, osmotic pressure, and light‐scattering measurements were conducted. We found this polymer to have a very broad molecular weight distribution. And, although fractionation by molecular weight was effected, the fractions retained a broad molecular weight distribution. Our data do not indicate significant branching for this polymer. As a result of our studies, we have theorized that a supermolecular structure may be present in this polymer.

SynopsisThe thermal stability of the polymer prepared by substituting poly(dich1orophosphazene) with an excess of a 64/36 mole-% mixture of the sodium salts of 2,2,2-trifluoroethano1/2,2,3,3,4,4,5,5-octafluoropentanol were studied by thermogravimetric and gel permeation chromatography techniques. The primary mode of degradation of this polymer was shown to be via random scission. The overall degradation reaction corresponds to quasi-zero-order kinetics. INTRODUCTIONA number of such elements as sulfur, phosphorus, silicon, etc., have been investigated as potential inorganic polymer backbones with thermal stabilities in excess of 250°C. However, as Economy and Mason' have pointed out, the utility of these elements is limited because of their inability to form chains longer than ten atoms. Furthermore, the bond strengths of these elements indicate that polymers from them may be less stable than carbon chains.Heteroatoms appear to show significantly higher bond strengths and thus offer the possibility of obtaining polymers with improved thermal ~tabilities.~,~ These heteroatoms also show relatively high ionic character which can lead to dipole interactions with neighboring chains thus resulting in brittle, glass-like behavior. These chain interactions may be minimized by encasing the metal ion in an organic shell. In the case of silicones, the stearic effects of alkyl groups diminish these chain interactions. If one considers the bond strengths of these inorganic elements alone, one may overestimate the stabilities of the resulting polymers since these inorganic bonds have an availability of bonding orbitals which may provide low-energy pathways to degradation reactions. ' The stability of polymeric materials has been judged on the ability of the polymer to retain its mechanical properties over an extended service time. It is also possible to establish a stability criterion of some value by following the weight loss of a polymer as a function of temperature or time. Experimentally, such weight loss data can be obtained from thermogravimetric analysis (TGA). However, because significant property changes may occur without a noticeable weight loss, great caution should be exercized in drawing conclusions from these data.* It is possible that the rate of weight loss may represent the rate of sublimation or distillation of degradation products rather than the rate of degradation of the polymer. The latter problem may be overcome if the rate of evaporation of the fragments is extremely fast as compared with the rate of formation of fragments.5Information obtained from thermal weight loss data are quite valuable from the screening point of view. However, when combined with other information, such as molecular weight changes, this method of determining thermal stability may be extremely valuable and can serve as a basis for the calculation of the activation energies of the overall degradation reaction.

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