Pseudo super‐miscibility: Blends of semi‐crystalline nylon pairs exhibiting a single Tg and a single Tm

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Abstract
Physical blends of nylon 6 (or nylon 66) homopolymer with random copolymers of nylon 6/nylon 66 or of nylon 6/nylon 12 were melt extruded into films and characterized by Differential Scanning Calorimetry (DSC) and X‐ray Diffraction (XRD) techniques. The films containing up to 50–65% of the copolymer exhibited only a single melting temperature (Tm) corresponding to that of the pure homopolymer without any trace of the otherwise crystallizable, lower melting copolymer component. These observations are quite unusual since the binary blends of the homopolymers of nylon 6, nylon 66, and nylon 12 exhibit their characteristic 2 Tm's. That result was significant in that at least 20% nylon 6 units (Tm = 222°C) can be incorporated into nylon 66 (Tm = 262°C) without any depression either in the Tm or in the crystallinity of nylon 66 while retaining its Tm = 262°C as the only melting phase. Also, it has now become possible to develop blend compositions based on ≥ 4 polyamide moieties that exhibit a single Tg, high crystallinity, and a sigle Tm corresponding to the higest melting component. We believe that the observed phenomenon, pseudo super‐miscibility, is kinetically driven (i.e., only the higher melting homopolymer crystallizes), rather than thermodynamically or crystallographically, since the structural units originate from polymers that are inherently not isomorphic. In view of the unexpected observation, at least in the field of nylons and its technological significance, we anticipate renewed interest in this area and more definitive understanding to emerge from future studies.

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