An AFM study on the structure and melting behavior of melt-crystallized isotactic poly(1-butene)

Spherulites with closely packed edge-on lamellae and lathlike flat-on crystals of melt crystallized isotactic poly(1-butene) in ultra-thin films at different temperatures were studied by AFM in taping mode. Starting from these different crystals, the melting processes of them after aging at room temperature for different periods of time were monitored. Through selective melting of the thermally less stable Form II crystals, the solid phase transformation of iPB-1 from Form II to I was discussed. Based on the obtained results, it is concluded that nucleation of the iPB-1 stable Form I crystals is the rate-determining step of the Form II to I conversion. Moreover, from the facts that (i) nucleation of the stable Form I crystals starts most likely at crystalline side surfaces or corners, and (ii) the phase conversion rate of the melt grown flat-on crystals is much faster than that of the solution grown single crystals, we suggest that residual local thermal stresses exist at the edges of the microcrystallites and stacking regularity of the crystalline lamellae play a very important role in generating the nuclei of the iPB-1 Form I crystals.