Crystallinity ethylene-octene copolymer

Fig. 18 Several samples of ethylene-octene copolymers having similar comonomer content, crystallinity, and melt index. Sample 3 is a physical blend of high and low density copolymers. Samples 4-6 are OBCs prepared with several different levels of chain shuttling agent. Reproduced by permission from [10]...

Melt compounding is most commonly utilized for the preparation of PO/silica nanocomposites. POs and their blends, such as PP [326-337], PE [338-343], ethylene-propylene copolymer [344-354], ethylene-octene copolymer [347], thermoplastic POs [348-350], PP/ EPDM [351,352], and PP/liquid-crystalline polymer (LCP) [353-357] blends, have been used as the matrices in the preparation of PO/silica nanosystems and nanomaterials by twin-screw extrusion and injection molding or lab-scale single-screw extrusion and compression molding. 

FIG. 7 Stress-strain curves in yield region for specific copolymers (a) ethylene-octene copolymers (b) ethylene-hexene copolymers (c) ethylene-butene copol5mers (d) schematic representation. Core level of crystallinity indicated with each curve. (From Ref. 9.)... 

Bensason et al. [81] reported the properties of a series of ethylene-octene copolymers made using Dow CGC technology. In addition to LLDPE, these products included plastomers having densities from 0.89 to 0.91 and crystalhnities between 23 and 39 percent and thermoplastic elastomers having densities below 0.89 and crystallinities between 10 and 23%. 

Content of Ot-Olefin. An increase in the a-olefin content of a copolymer results in a decrease of both crystallinity and density, accompanied by a significant reduction of the polymer mechanical modulus (stiffness). Eor example, the modulus values of ethylene—1-butene copolymers with a nonuniform compositional distribution decrease as shown in Table 2 (6). A similar dependence exists for ethylene—1-octene copolymers with uniform branching distribution (7), even though all such materials are, in general, much more elastic (see Table 2). An increase in the a-olefin content in the copolymers also results in a decrease of their tensile strength but a small increase in the elongation at break (8). These two dependencies, however, are not as pronounced as that for the resin modulus. 

Figure 4 Plot of degree of crystallinity (XDSC) from DSC against crystallinity (Xp) determined by density measurements. (A), hydrogenated polybutadienes ( ), ethylene 1-butene copolymers ( ), ethylene 1-octene copolymers. Reprinted with permission from Ref. [72]. Copyright 1984 American Chemical Society. 

Figure 10 Degree of crystallinity from WAXS, interfacial content from PALS and amorphous content from PALS for an ethylene 1-octene copolymers as a function of increasing 1-octene. Reproduced with permission from Ref. [158]. Copyright 2002 Elsevier Ltd.

Chang and co-workers (52,53) studied the large-scale deformation behavior and recovery behavior of semicrystalline ethylene-co-styrene polymers as a function of temperature, comonomer content, and crystallinity and compared them to the behavior of metallocene-produced ethylene/l-octene copolymers. Chen and co-workers (54) have provided an in-depth comparison of the morphological structure and properties of copolymers and confirmed that aspects of deformation that depended on crystallinity, such as yielding and cold drawing, were determined primarily by comonomer content for both sets of copolymers. 

The structure and elastomeric properties of the novel olefinic block copolymers (OBCs) were studied by DSC, WAXS, AFM combined with stress-strain, and strain recovery measurement. Their structure and properties were compared with the conventional statistical ethylene-octene (EO) copolymers. The OBCs showed higher strain recovery than the statistical EO copolymers, which is attributed to their unique crystalline morphology. AFM and WAXS studies revealed the elastic spherulites in OBCs. 

Polyolefin-based thermoplastic elastomers (TPEs) have received considerable attention due to their chemical inertness, low density, and low cost compared with other TPEs. Homogeneous ethylene-octene (EO) copolymers, synthesized via contemporary catalyst technology, with low crystallinity and low density (0.86-0.88g/cm ) exhibit the characteristics of thermoplastic elastomers. The elastomeric properties depend on the fringed micellar crystals which serve as network junctions. However, the low melting point of fringed micellar crystals have limited the application of elastic EO copolymers at higher temperatures. 

Random ethylene copolymers with small amounts (4-10 wt-%) of 7-olefins, e.g. 1-butene, 1-hexene, 1-octene and 4-methyl- 1-pentene, are referred to as linear low-density polyethylene, which is a commercially relevant class of polyolefins. Such copolymers are prepared by essentially the same catalysts used for the synthesis of high-density polyethylene [241]. Small amounts of a-olefin units incorporated in an ethylene copolymer have the effect of producing side chains at points where the 7-olefin is inserted into the linear polyethylene backbone. Thus, the copolymerisation produces short alkyl branches, which disrupt the crystallinity of high-density polyethylene and lower the density of the polymer so that it simulates many of the properties of low-density polyethylene manufactured by high-pressure radical polymerisation of ethylene [448] (Figure 2.3). 

Styrene undergoes copolymerisation with ethylene and various a-olefins in the presence of heterogeneous Ziegler-Natta catalysts. Its reactivity in the copolymerisation is quite low, which is illustrated by the values of the relative reactivity ratios, r and r2, presented in Table 4.5 [118]. One may note, however, a considerably high relative reactivity of styrene in copolymerisation with vinyl-cyclohexane. The copolymerisation of styrene with small amounts of a-olefin, such as 1-octene or 1-decene, yields copolymers of reduced crystallinity and thus reduced brittleness compared with the homopolymer of styrene. 

Polyolefin copolymers started with LLDPE and ethylene-propylene rubber (EPR). Today, there are polyolefin copolymers of ethylene with butene-1, hexene-1, octene, cyclopentene, and norbornene and copolymers of propylene with butene-1, pentene-1, and octene-1 in addition to ethylene. There are copolymers of butene-1 with pentene-1, 3-methylbutene-l, 4-methylpentene-1, and octene in addition to its copolymers with ethylene and propylene. There are copolymers of 4-methylpentene-1 with pentene-1 and hexene-1 in addition to its copolymers with butene-1 and propylene. The function of the comonomers is to reduce crystallinity, as compared to the homopolymers, resulting in copolymers that are highly elastomeric with very low... 

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