SynopsisX-ray diffraction and micrascopical investigation of test samples prepared by injection molding from composites of isotactic polypropylene with talc revealed a preferred orientation of the talc and polypropylene matrix. Contrary to the situation in polypropylene alone, the preferred Orientation in polypropylene-talc composites survived melting and a new crystallization. Crystallization rate measurements confirmed the nucleation activity of talc for polypropylene crystallization.

The morphology of poly@-oxybenzoate) polymerized from p-acetoxybenzoic acid (PABA) in constrained thin films at temperatures between 130" and 315 "C for various times is described.Polymerization below the melting point of the monomer, 196"C, occurs by a sublimationrecrystallization-melting process, with polymerization occuring in the melt. Lamellar crystals, often bilayered, are found that are ca. 100 A thick as well as single disclination domains. Electron diffraction patterns indicate the presence of either phase I or I1 in a given crystal, with the unit cell for phase I1 being proposed; the molecular axes are normal to the lamellae. Polymerization above 200 "C results in holes in the lamellae; it is suggested that polymerization also is in the form of lamellae followed by the hole formation as further reaction occurs in the crystalline state; initial "crystal" growth at all temperatures is in the liquid crystalline state.

The isothermal crystallization and phase II ! I transformation of bulk polybutene-1 at various temperatures have been characterized by x-ray diffraction. The crystallization rate can be increased or decreased by the addition of various solids, with sodium salicylate and talc, e.g., increasing the rate by .100% and, unexpectedly, decreasing the rate by .300%, respectively. The nucleating agents have no effect on the transformation rate, which, however, is increased slightly in the presence of water and ethanol and significantly in the presence of liquids that are solvents at elevated temperatures or by temperature cycling. As shown previously, the transformation rate of nontreated polymer is greatest near 258C, decreasing at higher and lower temperatures and is increased by tension or uniaxial compression.

SynopsisExamination of the isothermal crystallization and the effect of melting conditions on samples of isotactic polypropylene and its composite with talc, combined with electron-microscopic observation, has shown two types of heterogeneous nuclei effective in the crystallization process: (1) metastable nuclei, representing the unmelted crystalline phase of polypropylene, stabilized by solid heterogeneities, and operating after melting at relative low melting temperature and/or short melting time; and (2) stable crystallization nuclei, associated with solid heterogeneities, being probably catalyst residues. On the surface of these nuclei isotactic polypropylene tends to crystallize in an ordered fashion.

SYNOPSISInteraction in the system isotactic polypropylene-calcite was investigated using.X-ray diffraction and transmission electron microscopy. Calcite acts as a weak nucleation agent for polypropylene crystallization and its activity could be increased or decreased by a suitable surface treatment. Investigation of the morphology on the polypropylene-calcite interface using calcite single crystals disclosed the tendency of polypropylene for epitaxial crystallization along preferred substrate crystallographic directions. This tendency was analogous to polymer crystallization on other ionic crystals. I NTRO D UCTlO NThe properties of filled polymers differ in many respects from those of unfilled ones. The structure, morphology, and resulting properties depend mainly on the size, shape, orientation, amount, and distribution of filler particles and on the interaction of polymer and filler. For a given filled polymer system, knowledge of these factors is of great importance. It is relatively easy to gain information on filler structure and morphology. Problems arise in evaluating the interaction between a crystalline polymer and a solid filler.'^' According to their action, fillers are usually classified as inert or active. In case of active fillers, one can expect the filler influencing not only the process of polymer crystallization and melting but also the structure and morphology at the polymer-filler interface. This effect depends mainly on the character of the bond between polymer and filler. In polymers without functional groups which are capable of forming chemical bonds with the filler substrate (which is, e.g., the case for polyolefines filled with mineral fillers), bonding is realized by weak intermolecular forces ( electrostatic, induced dipole, and dispersion forces). Their energy is low and consequently the interfacial ashesion is lower than inside the polymer, where physical chain entanglements increase the cohesion.It is not yet understood whether the first mono- molecular polymer layer on the filler surface has an amorphous, mesomorphous, or crystalline character. Nevertheless, the setting down of molecular segments in an extended conformation with various perfection of lateral order could be assumed. Epitaxial overgrowth of the same polymer on substrates with different lattice parameters indicates that the polymer surface layer has an amorphous or mesomorphous ~t r u c t u r e .~'~ Usually, on this layer the polymer crystallizes in a stable crystal m~dification.~ Our investigation of the crystallization of linear polyethylene and its composites with solid fillers has shown the nucleation activity of talc and kaolin.' Morphological examination proved that polyethylene tends to crystallize on the basal planes of sheet silicates, epitaxially, in such a way that a system of parallel lamellae, oriented perpendicular to the basal plane of the substrate, grows out from the filler surface. Epitaxial lamellae tend to be aligned in a pseudohexagonal array, suggesting that polyethylene lamellae nucleate along ...