The solid state structure and properties of homogeneous copolymers of propylene and 1-hexene were studied by examining melting behavior, dynamic mechanical response, and morphology primarily with atomic force microscopy, wide- (WAXS) and small-angle X-ray scattering, and tensile deformation. Chain microstructure was analyzed by 13C NMR. The results indicate that copolymers used in this study have an essentially random distribution of comonomer. For copolymers with less than 10 mol% hexane, crystallinity decreases with increasing comonomer content, as expected for exclusion of comonomer from the polypropylene crystal. The peak melting and crystallization temperatures also decrease with increasing hexene content. Copolymers with more than 10 mol% hexane crystallize with a new crystal structure that permits incorporation of hexene units. This is inferred from a higher level of crystallinity than would be expected if comonomer were excluded from the crystal and better development of the crystals as the hexene content increases. Copolymers with the new crystal structure crystallize slowly. After an incubation period, long fibrous lamellae form sheaf-like arrays that develop into small spherulites. The corresponding enthalpy change as a function of time assumes an S-shape characteristic of a phase transition described by the Avrami process. The new crystallographic form has not been reported for either polypropylene or for poly(1-hexene). It follows from WAXS studies of highly oriented films that the crystallographic unit cell has orthorhombic symmetry with a = 1.9860 nm, b = 1.7176 nm, and c = 0.6458 nm. The most intense diffracting planes are identified as the (210) plane reflecting at 2θ = 10.30°, the (230) plane reflecting at 2θ = 17.65°, the (040) plane reflecting at 2θ = 20.60°, the (031) plane reflecting at 2θ = 20.73°, and the (112) plane reflecting at 2θ = 28.52° for Cu Kα radiation. On the basis of pole figures, it is evident that the easiest slip during plastic deformation of the new crystal form occurs along (0k0) planes.

Films with a thousand alternating layers of isotactic polypropylene (PP) and polystyrene (PS) were prepared by layer-multiplying coextrusion. The crystal structure of extremely thin PP layers confined between PS layers was studied by optical light microscopy (OM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS). Changes in structure were observed as the PP layer thickness decreased to the nanoscale. The thin PP discoids were largely composed of edge-on lamellae with (040) planes lying flat on the interface. In layers 65 and 10-nm thick, compressed d-spacings in the directions perpendicular to the chains and loss of registry along the chain axis were suggestive of smectic packing of conformationally distorted chains. Even so, crystalline lamellae were distinguishable in the AFM images. In addition to the crystal population with (040) planes parallel to the interface, the WAXS from layers 65-nm thick revealed another crystal fraction with (110) planes parallel to the interface and (040) planes perpendicular to the interface. This fraction was more evident in layers 10-nm thick, where it accounted for approximately 10 -20% of the crystallinity. Decreasing layer thickness resulted in a change of the crystal growth plane from the usual (110) to the more rare (010). The new crystal structure possibly served to fill-in the radial structure of the dendritic discoids when a limitation to the thickness of the layer left only a little space for secondary nucleation of the crosshatched lamella.

In the present study we examined the oxygen-transport properties of poly(ethylene naphthalate) (PEN) isothermally crystallized from the melt (melt crystallization) or quenched to the glass and subsequently isothermally crystallized by heating above the glass transition temperature (cold crystallization). The gauche/trans conformation of the glycol linkage was determined by infrared analysis, and the crystalline morphology was examined by atomic force microscopy (AFM). Explanation of the unexpectedly high solubility of crystallized PEN required a two-phase transport model consisting of an impermeable crystalline phase of constant density and a permeable amorphous phase of variable density. The resulting relationship between oxygen solubility and amorphous-phase density was consistent with free volume concepts of gas sorption. Morphological observations provided a structural model for solubility and permeability. The model consisted of a permeable amorphous matrix of constant density containing dispersed spherulites of lower permeability. The spherulites themselves were composites of impermeable crystallites and permeable interlamellar amorphous regions of lower density than the amorphous matrix. Dedensification of the interlamellar amorphous phase was due to the constrained nature of amorphous chains anchored to crystallites.

The solid‐state structure and properties of homogeneous copolymers of propylene and 1‐octene were examined. Based on the combined observations from melting behavior, dynamic mechanical response, morphology with primarily atomic force microscopy, X‐ray diffraction, and tensile deformation, a classification scheme with four distinct categories is proposed. The homopolymer constitutes Type IV. It is characterized by large α‐positive spherulites with thick lamellae, good lamellar organization, and considerable secondary crystallization. Copolymers with up to 5 mol % octene, with at least 28 wt % crystallinity, are classified as Type III. Like the homopolymer, these copolymers crystallize as α‐positive spherulites, however, they have smaller spherulites and thinner lamellae. Both Type IV and Type III materials exhibit thermoplastic behavior characterized by yielding with formation of a sharp neck, cold drawing, strong strain hardening, and small recovery. Copolymers classified as Type II have between 5 and 10 mol % octene with crystallinity in the range of 15–28%. Type II materials have smaller impinging spherulites and thinner lamellae than Type III copolymers. Moreover, the spherulites are α‐negative, meaning that they exhibit very little crystallographic branching. These copolymers also contain predominately α‐phase crystallinity. The materials in this category have plastomeric behavior. They form a diffuse neck upon yielding and exhibit some recovery. Type I copolymers have more than 10 mol % octene and less than 15% crystallinity. They exhibit a granular texture with the granules often assembled into beaded strings that resemble poorly developed lamellae. Type I copolymers crystallize predominantly in the mesophase. Materials belonging to this class deform with a very diffuse neck and also exhibit some recovery. They are identified as elastoplastomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4357–4370, 2004

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