In the rich and long-standing literature on the flow-induced formation of oriented precursors to polymer crystallization, it is often asserted that the longest, most extended chains are the dominant molecular species in the “shish” of the “shish-kebab” formation. We performed a critical examination of this widely held view, using deuterium labeling to distinguish different chain lengths within an overall distribution. Small-angle neutron-scattering patterns of the differently labeled materials showed that long chains are not overrepresented in the shish relative to their concentration in the material as a whole. We observed that the longest chains play a catalytic role, recruiting other chains adjacent to them into formation of the shish.

Characteristic cylindrical structures formed by ABC star-shaped terpolymers were investigated by microbeam small-angle X-ray scattering (SAXS) in addition to transmission electron microscopy (TEM). The polymer samples are composed of polyisoprene (I), polystyrene (S), and poly(2-vinylpyridine) (P); their volume ratios for I:S:P are 1:1:X, where X equals 0.7, 1.2, 1.3, and 1.9. The spotlike diffraction patterns were observed by microbeam SAXS due to scattering from a small number of ordered grains in the polymer samples, where the exact packing manners of the cylinders, or their lattice constants, have been clarified. In short, it has been found that the cross-sectional patterns of these tilings have the features of four Archimedean tiling patterns, i.e., (6.6.6), (4.8.8), (3.3.4.3.4), and (4.6.12). All the four SAXS patterns are quite consistent with the structural observation by TEM with regard to the crystallographic data.

The morphology of ADMET-synthesized polyethylene with n-butyl branches precisely spaced on every 39th carbon (EH39) was studied in comparison with an ethylene/1-hexene addition copolymer possessing the same branching probability, the goal being to elucidate the effect of the intramolecular sequence length heterogeneity on the lamella crystal thickness and its distribution. EH39 was found to have an orthorhombic crystalline polymorphism, which is normal for commercialized polyethylenes and different from that of the other ADMET polyethylenes with shorter CH 2 spacing (C15, C21). EH39 exhibits a narrow lamella thickness distribution; the average thickness (l c,av. ) corresponds exactly to the space length between two consecutive branches, suggesting the complete exclusion of n-butyl branches from the crystal stem. The average thickness, l c,av. mentioned above is also coincident with that obtained from WAXS and SAXS. On the other hand, the 1-hexene copolymer forms much thicker lamellae and a broader thickness distribution than ADMET polyethylene. Here, the average thickness l c,av. determined by TEM observation of the copolymer is 1.5 times larger than that calculated from the most probable ethylene sequence length obtained from 13 C NMR, or for a theoretical ethylene sequence length distribution, indicating that the lamellae are composed predominantly of the sparsely branched longer ethylene sequences that are statistically included. The intramolecular sequence distribution is considered significant to determine the lamella thickness and thickness distribution for short chain-branched polyethylenes with a narrow intermolecular chemical composition distribution.

The process of rearranging lamella crystal structures in isotactic polypropylene (iPP) and butene randomly copolymerized iPP (bPP) spherulites during hot drawing was investigated by in-situ microbeam smallangle X-ray scattering (SAXS)-wide-angle X-ray scattering (WAXS)-polarized optical microscopy (POM) simultaneous measurements. We subjected a fixed position in an upper quadrant of a spherulite, which is stretched in the horizontal direction, to microbeam X-ray irradiation, and observed local structural changes, such as those in ordered crystal size and orientation, and a lamella stacking structure. We successfully obtained the structural information on parent and daughter lamellae in various orientations. In iPP, the long period of perpendicular parent lamellae increased, and then the disordering of crystal packing structures along the a-axis started. When necking started, the long periods of parent and daughter lamellae drastically started to decrease with the alignment of the c-axis in the stretching direction. The ease of crystal fragmentation and c-axis alignment strongly depended on the type of lamella, indicating the order of stress concentration during drawing. In bPP, it was found that the alignments of all the lamellae occur almost simultaneously and that parent and daughter lamellae independently rotate until necking.

Lamella thickness distribution (LTD) plays a critical role in determining the mechanical properties of polyethylene. LTD is predominantly governed by the intermolecular chemical composition distribution, but intrachain heterogeneity also results in a broadened LTD. Polyethylene synthesized by acyclic diene metathesis (ADMET) contains pristine microstructures free from inter and intrachain heterogeneity and therefore represent ideal models to investigate these phenomena. The crystalline structures of ADMET polyethylene with ethyl or n-hexyl branches every 21 st backbone carbon (EB21and EO21, respectively) were characterized by transmission electron microscopy (TEM), small X-ray scattering and wide angle X-ray diffraction (SAXS and WAXD), and differential scanning calorimetry (DSC). The samples were crystallized for various periods at temperatures near the DSC crystallization peak temperatures: 10 8C for EB21 and 0 8C for EO21. TEM observation exhibited that EB21 displays straight lamellar crystals with axialitic organization and an average thickness of about 55 Å. This corresponds to twice the ethylene sequence length between branches, suggesting that one lamellar stem spans three branches and includes one ethyl branch within the lamella. The lamella thickness distribution was very narrow compared with that of the cross-fraction of ethylene/1-butene copolymer prepared via Ziegler-Natta polymerization. Similarly it was found from the same characterization methods that EO21 also displays a narrow lamella thickness distribution albeit with thinner lamellae, averaging 25-26Å thick. Judging from this lamella thickness, EO21 is considered to have a lamella stem composed of a single ethylene sequence between two braches, suggesting that the n-hexyl branch is entirely excluded from a crystalline phase.

Depending on the degree of short chain branch (SCB) incorporation, the crystallization behavior and resultant crystalline structure drastically change in polyethylene with precisely spaced branches. In polyethylene with hexyl branches precisely spaced on every 21st carbon (HB21), only crystallization mediated by a transient hexagonal phase without incorporation of the SCB was observed. On the other hand, in polyethylene with ethyl branches precisely spaced on every 21st carbon (EB21), crystallization behavior was strongly dependent on the crystallization temperature. A thin lamella was formed through crystallization mediated by a hexagonal phase and no thickening occurred at 5–8 °C, while thickening of the transient hexagonal lamellae occurred at 10–15 °C, and one SCB seemed to be incorporated into a crystal stem. At 17 °C, no thickening of the hexagonal phase occurred and a hexagonal phase with sufficient lamella thickness was directly formed from the melt. At 21–28 °C, crystallization mediated by hexago..

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