Density copolymers

Properties unfilled Fow-density Medium-density High-density weight high-density copolymer... 

Obviously, there exists severe interplastics competition, e.g. PP vs. ABS, clarified PP vs. PS, PA, PVC, HDPE and PS (Table 10.7). A wide range of cross-linked and thermoplastic elastomer applications, from footware to automotive parts and toothbrushes, are adopting new metallocene-catalysed polyolefin elastomers (POEs). These low-density copolymers of ethylene and octene were first accepted as impact modifiers for TPOs, but now displace EPDM, (foamed) EVA, flexible PVC, and olefinic thermoplastic vulcanisates (TPVs). Interpolymer competition may also result from... 

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]...

Low cycle fatigue testing, 13 489, 491-493 Low density copolymer resins, for extrusion coating, 20 235t... 

The melting point is also somewhat dependent on the crystal size, in particular, when the crystals are very small, Tm is lower. This is, i.a., caused by the restrictions in chain conformations near the crystal surface. A spread in crystal size, therefore, also contributes to the presence of a melting region. This is clearly demonstrated by the (new) PE grades with very low density (copolymers of ethylene with e.g. 1-octene) the crystallites are so small that for a grade with d =.86 the melting point is only 30 °C ... 

For the production of ethylene/l-octene copolymers, metallocenes in combination with oligomeric methylalumoxanes or other compounds are now used [31, 63]. Half-sandwich transition metal complexes such as [(tetramethyl- / -cyclopentadienyl) (A-/-butylamido)dimethylsilyl]titanium dichloride are applied to synthesize linear low-density copolymers and plastomers, called constrained geometry catalysts [31]. Ethylene and styrene can be copolymerized to products ranging from semicrystalline mbber-like elastomers to highly amorphous rigid materials at room temperature [64]. 

Although a large share of the EP co-polymers and EPD terpolymers is still manufactured with vanadium-based catalysts at low temperature, metallocene catalysts have added a whole new dimension to EP co-polymerization, and to the range of material properties that can be achieved, as has been the case for the ethylene-based low-density copolymers discussed in the previous section. The subject of EP co-polymerization with group 4 bis(cyclopentadienyl) complexes has been reviewed in detail up to 1998.59... 

The extension of brush molecules is caused by excluded volume repulsion of the 2D-adsorbed side chains. Therefore, the length of adsorbed brushes should also depend on the grafting density. Copolymer brushes with a random sequence of methyl methacrylate and poly(n-butyl acrylate)-substituted methacrylate units were prepared with different compositions, i.e., grafting densities. Table 3 com-... 

FIGURE 227 Differential scanning calorimetry of two 0.92 g mL 1 density copolymers, one made with Cr/silica and the other with a metallocene catalyst. 

As noted above, the melting (or swelling) point of the polymer in isobutane depends on the degree of branching in the resin, that is, its density. Lower density resins, which contain less crystallinity, melt at lower temperatures. Thus, the lower-density copolymers must be manufactured at lower reaction temperatures. 

Polyampholytes. Ampholytic copolymers (i, 30-35) exhibit interesting viscosity behavior in electrolyte solutions that is quite opposite to the behavior of conventional polyelectrolytes. Recently we prepared high charge density copolymers from the matched, nonhydrolyzable comonomer pairs sodium 2-acrylamide-2-methylpropanesulfonate (NaAMPS) and 2-acrylam-ide-2-methylpropanedimethylammonium chloride (AMPDAC) (1, 33) see structures). 

Alathon L 4903. A high molecular-weight, high density copolymer with broad bimodal molecular weight distribution. This resin exhibits excellent machine-direction tear in an HMW-HD resin as well as low gel levels. 

Table 15. Low Density Copolymer Resins for Extrusion Coating ...

ULDPE and VLDPE resins find application in low temperature applications, such as ice bags, where lower density offers greater toughness. They are also used as sealing layers, replacing low density copolymers such as vinyl acetate, and as blend components to improve toughness. 

Polyethylene is classified by density. Type I has a density of up to 0.925 and is called low density (LDPE). Type II has a density range from 0.926 to 0.940 and is called medium density (LMDPE) most LLDPEs fall into this range. Type III has a range from 0.941 to 0.969 and is classified as high density copolymer (HDPE). Type IV is above 0.960 and is classified as high density homopolymer it is not used in rotational molding. 

Minick, J. Moet, A. Hiltner, A. Baer, E. Chum, S. P. Crystallization of very low density copolymers of ethylene with a-olefins. J. Appl. Polym. Sci. 1995, 58, 1371-1384. 

The high-charge-density copolymers or the large-molecular-weight homopolymers are not the best detergent polymers under all washing conditions and for all of the wanted performance features, in spite of their higher sequestration capacities. Other features are often... 

Figure 5.55. Banded spherulites are observed in TEM of perman-ganically etched, high density copolymer exhibiting a mature banded structure (A). Intermittent contact mode AFM images of the same polymer are shown in a normal height image (B) and in a three dimensional height image (C). (From Janimak et al. [271], (2001) Elsevier used with permission.)...

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