Structure Evolution of Propylene-1-Butylene Random Copolymer under Uniaxial Stretching: from Unit Cells to Lamellae

Crystallization changes of propylene-1-butylene (P-H) random copolymer with low butylene content (5.7 mol\%) under uniaxial tensile deformation at high temperature (100 $^{\circ}$C) was investigated using time-resolved wide- and small-angle X-ray scattering (WAXS/SAXS) techniques. Structure and preferred orientation at length scales of crystal unit cell and lamellae were investigated explicitly using 2D whole pattern analysis. $\gamma$-phase was found to be the dominant initial modification which was transformed into $\alpha$-phase during stretching, forming more stable parallel packed polymer chains in the unit cell. 2D WAXS analysis enabled us to identify three orientation modes from different crystal forms, i.e., $\gamma$-phase with tilted cross-$\beta$ configuration, $\alpha$-phase with parallel chain packing and \emph{a}-axis orientation of $\alpha$-form crystals in daughter lamellae. 2D SAXS analysis based on stacking model enabled us to understand the development of the four-point pattern under deformation.