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.
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
-The fracture surfaces of a Zr-based bulk metallic glass exhibit exotic multi-affine isotropic scaling properties. The study of the mismatch between the two facing fracture surfaces as a function of their distance shows that fracture occurs mostly through the growth and coalescence of damage cavities. The fractal nature of these damage cavities is shown to control the roughness of the fracture surfaces. [17,18] have shown to be self-affine, with a roughness exponent ζ ≈ 3/4 in spite of huge differences in the fracture mechanisms. It was therefore suggested [5,19] that ζ might have a universal value, i.e., independent of the fracture mode and of the material.More recently, it has been shown [11,13] that fracture surfaces are anisotropic, i.e. when profiles along the direction of crack propagation are considered, the roughness exponent is equal to β 0.6. Bonamy et al. [12] have shown that the set of exponents {ζ 0.75, β 0.6} define a universality class corresponding to length scales smaller than the process zone size, where non linear elastic processes take place. Above this process zone size, another university class is observed [12,20,21] characterized by a set of exponents {ζ 0.4, β 0.5} that can be understood theoretically within the Linear Elastic Fracture Mechanics framework.A third regime arises at very small length scales, characterized by a roughness index close to ζ ≈ 0.5, observed in a metallic alloy and in a soda-lime silicate glass [8][9][10] along a direction perpendicular to the direction of crack propagation. This regime was suggested [22] to be
ABSTRACT:This study compared a series of experimental propylene/ethylene copolymers synthesized by a transition metal-based, postmetallocene catalyst (xP/E) with homogeneous propylene/ethylene copolymers synthesized by conventional metallocene catalysts (mP/E). The properties varied from thermoplastic to elastomeric over the broad composition range examined. Copolymers with up to 30 mol % ethylene were characterized by thermal analysis, density, atomic force microscopy, and stress-strain behavior. The xP/Es exhibited noticeably lower crystallinity than mP/Es for the same comonomer content. Correspondingly, an xP/E exhibited a lower melting point, lower glass transition temperature, lower modulus, and lower yield stress than an mP/E of the same comonomer content. The difference was magnified as the comonomer content increased. Homogeneous mP/Es exhibited space-filling spherulites with sharp boundaries and uniform lamellar texture. Increasing comonomer content served to decrease spherulite size until spherulitic entities were no longer discernable. In contrast, axialites, rather than spherulites, described the irregular morphological entities observed in xP/Es. The lamellar texture was heterogeneous in terms of lamellar density and organization. At higher comonomer content, embryonic axialites were dispersed among individual randomly arrayed lamellae. These features were characteristic of a copolymer with heterogeneous chain composition.
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