Crystallization, Melting, and Morphology of Syndiotactic Polypropylene Fractions. 3. Lamellar Single Crystals and Chain Folding

Abstract

Highly faceted, regular, lathlike lamellar single crystals of syndiotactic polypropylene (s-PP) fractions have been investigated through transmission electron microscopy (TEM), atomic force microscopy (AFM), and electron diffraction (ED). Single crystals of s-PP over 1 μm in size can be grown from the melt in thin films. ED results obtained from the s-PP single crystals indicate a unit cell III with a = 1.450 nm, b = 1.120 nm, and c = 0.740 nm as proposed by Lovinger and Lotz. At high crystallization temperatures, relatively low molecular weight s-PP fractions can grow lamellar single crystals with microsectors. The polyethylene decoration method has been used to identify the chain folding direction, and no preferred orientation has been observed on the nonsectorized lamellar crystals. Sectorized lamellar single crystals show two different regions. In the sectors along the long axis (the b-axis), the chain folding is found to be parallel to the 010 direction. In the sectors along the short axis (the a-axis), little preferred orientation can be found. The deformation method of nonsectorized, high molecular weight s-PP single crystals on a plastic film has also been utilized to determine the chain folding direction. Microfibrillar structures can be observed in the cracks of the single crystals along both the a- and b-axes after deformation. This indicates that the folding direction in these nonsectorized, high molecular weight s-PP single crystals may be either along the (110) planes or a combination of the (100) and (010) microfolding and microsectoring. Zigzag-shaped edges on the deformed single crystals along the a-axis are also observed, and the sliding planes can be identified as the (110) planes.

Impact of Nanoscale Confinement on Crystal Orientation of Poly(ethylene oxide)

“…Depending on the specific polymer, the literature describes the preferred orientation as either on-edge or in-plane, which suggests that only one side of the transition was found. It is noteworthy that rapidly crystallizing polymers, such as polyethylene [4] and isotactic polypropylene, [3,32] are reported to form on-edge crystals and more slowly crystallizing polymers, such as isotactic PS [33] and syndiotactic polypropylene, [34] apparently form in-plane crystals.…”

Crystallization in Polymer Thin Films: Morphology and Growth

“…There are only a few reports of single crystals from thin films in the literature. These are syndiotactic polypropylene (s-PP), 53,54 i-PS, [55][56][57] PLLA, 38,58 PEO, 59,60 and PCL. 26 Each has a unique morphology.…”

Nonisothermal crystallization of s-PP fractions

“…The isothermal crystallization and the morphology of s-PP was also extensively studied. [7][8][9][10][11][12] However, there are few reports on the nonisothermal crystallization of s-PP. On the other hand, the crystallization behavior and crystal structure of s-PP were found to strongly depend on the stereodefects in the polymer chain and molecular weight.…”