Phase transformation in poly(1-butene) upon drawing

Isotactic poly(l-butene) (PB-1) films, consisting either of crystal form II I (solution-grown crystal mat) or I' (melt-crystallized film under a high p ressure), were drawn uniaxially by tensile draw and solid-state coextrusion in the range of room temperature to 80 degrees C, below their melting temp eratures (T-m = 90-100 degrees C). The phase transformations induced by dra w were characterized by WAXD and DSC. The results are discussed in terms of the effect of drawing variables on the deformation mechanism of PB-1. Tens ile draw, which proceeded with a clear neck, was variable and affected by t he initial crystal forms and draw temperatures. Upon the tensile draw of fo rm I' films, oriented unstable form II crystals were formed independently o f draw temperatures. They spontaneously transformed into the stable form I, as reported. When the form III mat was tensile drawn at 80 degrees C, near its T-m, oriented form II crystals were obtained, whereas the draw at a lo wer temperature of 70 degrees C produced oriented form I' crystals. Crystal form II is known to form only by crystallization from the random chain con formation, including melt, glass, and solution. Thus, the formation of the form II on tensile draw suggests that the deformation had proceeded thoroug h quasi-melting followed by recrystallization into the oriented form II. In contrast to the tensile draw with a neck, solid-state coextrusion, where t he deformation proceeds gradually within an extrusion die, produced oriente d form I' crystals independently of the initial crystal forms and extrusion temperatures. This suggests that the deformation on solid-state coextrusio n proceeded in the crystalline state. These results indicate that the draw of PB-1 proceeds either through quasi-melting/recrystallization or in the c rystalline state depending on the draw technique and temperature and the cr ystal form of the initial starting sample.