MISCIBILITY OF POLYAMIDE BLENDS .2. THERMAL STUDY OF POLY(HEXAMETHYLENE ISOPHTHALAMIDE) NYLON-N,M BLENDS

Miscibility of a series of nylons-6,m with poly(hexamethylene isophtha lamide), abbreviated 6I nylon, was investigated. Four polyamides (nylo n-6,5, nylon-6,7, nylon-6,8, and nylon-6,9) were found miscible, on a DSC scale, with 6I nylon. A series of nylon-n,m which had the same num ber of CH2 groups as nylon-6,7 was also studied; no miscible blend wit h 6I nylon was found. This was taken as direct evidence of the importa nce of average interamide distances for miscibility. Negative deviatio ns from linearity in T-g-composition behavior of the blend are propose d to stem from conformational changes leading to weaker van der Waals interactions. These weak interactions are counterbalanced, In terms of energy, either by more ordered hydrogen bond networks or by entropy e ffects. For nylon-6,8/6I nylon blend, an S-shaped curve was observed, which is attributed to the occurrence of variations of Chain morpholog ies with blend composition.