Structure and physical properties of syndiotactic polypropylene oriented from different polymorphs

Two syndiotactic polypropylene (sPP) samples were obtained by quenching the melt in a bath at 0 degreesC for 1 min (sample 1A, crystallized in the hel ical form I), and for 3 days (sample 1B, in the trans-planar mesophase). Sa mples 1A and 1B were drawn at room temperature obtaining fibers with draw r atios lambda = 5, 6, and 7. The fibers were analyzed under stress by X-rays and FTIR, successively unhooked, and again analyzed. Different structural organizations were found in the fibers fixed or relaxed. In sample 1B, the drawing produced a progressive orientation of the trans-planar mesophase en ding with the formation of the crystalline trans-planar form III. On releas ing the tension, form III transformed again into the trans-planar mesophase , but very weak helical reflections appeared in the X-ray patterns. Infrare d spectra confirmed that one of the helical bands increases on releasing th e tension. In sample 1A, the helical form I was first oriented and then, by progressive drawing, transformed into the crystalline trans-planar form II I. Releasing the tension, form III again converted into the helical form I and partially into the trans-planar mesophase. Despite the different struct ural organizations, all the relaxed fibers showed a good elasticity and the same qualitative behavior. It is characterized for all the fibers by a low hysteresis and a small permanent set after a 50% deformation. However, the elastic fibers show a much higher modulus than the conventional elastomers .