The Βα Growth Transition of Isotactic Polypropylene During Stepwise Crystallization At

Supplementary Information

The βα Growth Transition of Isotactic Polypropylene During Stepwise Crystallization at Elevated Temperature

Jiying Wang, Zhongjie Ren, Xiaoli Sun, Huihui Li* and Shouke Yan

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.

Correspondence to: Huihui Li (E-mail: Tel: 0086-10-64426375)

Figure S1 Optical micrographs of iPP film, which was first crystallized isothermally at 135 oC for 20 min, and jumped to 151 oC for 150 min further isothermal crystallization (a), then heated to 160 oC (b), 170 oC (c), at 2 oC/min. The αiPP spherulite and β-hexagonite are indicated by white arrows and labeld as α and β.

It can be seen from Figure S1a that the αiPP spherulite is composed of two regions which was crystallized at 135 and 151 ºC respectively. The β-hexagonites are also composed of two regions, i.e. the β hexagonite crystallized at 135 ºC and the surrounded α crystals transformed at 151 ºC. From Figure S1b, one can see when the sample was heated to 160 ºC, the β hexagonites melted first, but α crystals around the β hexagonites and the α spherulite remain. It can be found at higher temperature, the α spherulite which was crystallized at 135 ºC melt, and those crystallized at 151 ºC survived (Figure S1c). That means the α crystals crystallized at higher temperature have much more perfect structure, leading to higher melting point.

Figure S2 (a) The POM micrograph of an β-iPP hexagonite, which was prepared by first crystallization at 135 oC for 20 min, then jumped to 145 oC for 70 min and quenched to room temperature in the end, and (b) the SEM micrograph of the region indicated by a rectangle in (a), the lamellae crystallized at 135, 145 oC and during quenching process was indicated by the white arrows labeled 1, 2, 3 respectively.

A βiPP hexagonite can be observed in Figure S2a, and the SEM micrograph shown in Figure S2(b) can present more details about the lamellar structure crystallized at different temperatures. The lamellae shown in Figure S2b are obviously layered lamellae seen flat-on, which is the characteristic of βiPP crystals. A closer observation found these lamellae are composed mainly of three regions, i.e. the lamellae crystallized at 145 oC have the biggest size, whereas the ones crystallized during quenching process show the smallest size. Moreover, it can be seen that much more etching pits appeared on the surface of lamellae grown during quenching process, indicating the more screw dislocations on these lamellae.