| Abstract: | Blends of isotactic polypropylene and polyethylene or polyamides often display highly unusual crystalline morphologies in which the chain axes of the helical and linear polymers are at large angles to each other. These crystalline morphologies are explained on the basis of a specific epitaxial relationship that rests on the existence, in the (010) plane of iPP, of rows of methyl groups nearly 5-Å apart. The structural basis of all the observed morphologies is the parallel alignment of the aliphatic segments of the PE or polyamides and of the iPP methyl rows (or vice versa) and matching of the near 5-Å distances between PE or PA chains and iPP methyl rows. The implications of this unusual epitaxial relationship with respect to the apparent “universality” of polymer nucleating agents are examined. |
