Diblock copolymers show a menagerie of morphologies1 as a function of the relative lengths of the blocks and the temperature (or the magnitude of x-N, where x is the Flory interaction parameter and N the degree of polymerization). These structures range from spheres to hexagonally ordered cylinders and lamellae, corresponding to decreasing mean curvature of the interphase boundary. More recently2 a three-dimensionally ordered structure called the ordered bicontinuous double diamond (OBDD) phase is found at styrene compositions 4>s between 0.62 and 0.66 for polystyrene-6-polyisoprene diblock copolymers. When a homopolymer is mixed with a diblock copolymer, the occurrence of macrophase separation adds a new dimension to the possible morphological variations that can be realized, and the phase diagrams of such blends exhibit fascinating complexities.3,4 Even when the amount of added homopolymer is below its solubility limits so that a single macroscopic phase is realized, a range of structure,

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The crystallization behavior and crystalline structure of a series of chlorine-containing polyethylenes (PEs) with either a random or a precise placement of the Cl atom on each and every 21st, 19th, 15th, and 9th backbone carbon have been studied by DSC, NMR, Raman spectroscopy, WAXD, SAXS and AFM in samples cooled from the melt at 1°C/min. All precision Cl-substituted PEs crystallize as homopolymers based on their DD/MAS solid-state 13 C NMR spectra that reveal a uniform distribution of the content of halogen between crystalline and noncrystalline regions. In addition, unique WAXD crystallographic patterns that differ from those of the linear PE and random polymers, relatively large crystal thicknesses, and sharp crystallization and melting peaks also support this homopolymer pattern in precision systems. In contrast, a high concentration of Cl in the noncrystalline regions in the case of the random systems suggest that the crystallization process for randomly substituted samples is being led by the selection of the most crystalline sequences, resulting in broad thermal transitions and lower crystallinities. Increasing chlorine content in both precision and random systems decreases crystallinity, melting temperature, heat of fusion, and crystallite thicknesses suggesting that Cl atoms are defects that hinder the crystallization of these polyolefins. Both systems are found to exhibit a lamellar crystalline morphology. Precision substituted polyethylenes form long, straight, and stacked lamellae with axialitic (PE21Cl, PE19Cl, and PE15Cl) or spherulitic (PE9Cl) organization as typical of homopolymers of similar molar mass. In contrast, the lamellae of random analogs are curved and more segmented as found in other PE random copolymers. The distribution of Cl within the crystalline regions of systems with precision substitution is strongly affected by the sequence length of the methylene groups. Packing around the substitution point of PE21Cl, PE19Cl, and PE15Cl render nearly all-trans conformations and asymmetric Cl distribution, while close staggering of Cl atoms in the crystals of PE9Cl exert conformational distortions as observed by a strong increase of TG conformers in the Raman spectra.