Aliphatic polyamides, relaxations

Dynamic-mechanical and dielectric data have been widely reported for most aliphatic polyamides, especially poly(g-caprolactam) (nylon-6 or PA-6 rg 313K) and poly(hexamethylene adipamide) (nylon-6,6 or PA-6,6 Tg 323 K). Results of dynamic-mechanical and dielectric measurements of PA-6 and PA-6,6 (Table 13.8) provide evidence for three relaxations (/3, y, and 8) in these polymers at temperatures below their crystalline-melting temperature Tni (487-506 K for PA-6 and 523-545 K for PA-6,6) [8]. The /3 relaxation (located at above 310-347 K for PA-6,6 and 357-370 K for PA-6,6) is associated with high... 

In amorphous polymers the glass transition and the relaxation behavior associated with it are very sensitive to the addition of small amounts of diluents. As the diluent is added, the relaxation is shifted to a lower temperature at constant frequency or higher frequency at constant temperature. The usual explanation is that since the diluent molecules are small and mobile, they act to effectively increase the available free volume for segmental motion and hence speed it up. Similar plasticizing effects on the glass-rubber transition in semicrystalline polymers are observed. One such example is the case of poly(vinyl alcohol), which is water-soluble (Takayanagi 1965). Other examples of semicrystalline polymers where the effects of moisture are observed are aliphatic polyamides such as Nylon 6-6 (Starkweather 1980), Nylon 6-10 (Boyd 1959 Woodward et al. I960), and Nylon 12 (Varlet et al. 1990). 

The structure of an amorphous polyamide prepared from hexamethylenediamine and isophthalic/tere-phthalic acids was modified in order to determine the effect of chemical structure on the oxygen permeation properties. The greatest increase in permeation was obtained by lengthening the aliphatic chain. Placement of substituents on the polymer chain also led to increased permeation. Reversal of the amide linkage direction had no effect on the permeation properties. Free volume calculations and dielectric relaxation studies indicate that free volume is probably the dominant factor in determining the permeation properties of these polymers. 

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