Ethylene random, crystalline

Polypropylene, PP, was blended with a random crystalline terpolymer of 96-85 wt% propylene, 1.5-5.0 wt% ethylene, and 2.5-10 wt% C4 g alpha-olefin. The blends were used to manufacture strands of multiple monofilamcmts m staple fibers with high resiliency and shrinkage, for pile fabric. 

Fig. 7. Glass-transition temperature (Tg) versus ethylene concentration in propylene-ethylene random copolsmier using aspeciflc catalyst (no crystallinity). Values were determined by differential scanning calorimetiy (DSC).

Similarly, the random introduction by copolymerization of stericaHy incompatible repeating unit B into chains of crystalline A reduces the crystalline melting point and degree of crystallinity. If is reduced to T, crystals cannot form. Isotactic polypropylene and linear polyethylene homopolymers are each highly crystalline plastics. However, a random 65% ethylene—35% propylene copolymer of the two, poly(ethylene- (9-prop5lene) is a completely amorphous ethylene—propylene mbber (EPR). On the other hand, block copolymers of the two, poly(ethylene- -prop5iene) of the same overall composition, are highly crystalline. X-ray studies of these materials reveal both the polyethylene lattice and the isotactic polypropylene lattice, as the different blocks crystallize in thek own lattices. 

The process yields a random, completely soluble polymer that shows no evidence of crystallinity of the polyethylene type down to —60°C. The polymer backbone is fully saturated, making it highly resistant to ozone attack even in the absence of antiozonant additives. The fluid resistance and low temperature properties of ethylene—acryUc elastomers are largely a function of the methyl acrylate to ethylene ratio. At higher methyl acrylate levels, the increased polarity augments resistance to hydrocarbon oils. However, the decreased chain mobiUty associated with this change results in less fiexibihty at low temperatures. 

Copolymerization e.g., of 1-butene or 1-hexene with ethylene, gives short-chain branching-, e.g., the branches contain three or five carbon atoms. The random location of the side-chains lowers the crystallinity and density. Long-chain branching refers to branches that are similar in length to the polymer backbone and this type occurs in polyethylene manufactured using the... 

Figure 3 Non-linear least-squares curve fitting of the orthorhombic WAXS profile of an ethylene 1-decene random copolymer with 2.7 mol% branches. The two crystalline reflections and the amorphous halo are shown. 

For example, a PE-fe-poly(ethylene-co-propylene) diblock composed of crystalline PE and amorphous ethylene/propylene copolymer segments was synthesized from ethylene and ethylene/propylene. The addition of MAO and Ti-FI catalyst 40 (Fig. 25) to an ethylene-saturated toluene at 25 °C resulted in the rapid formation of a living PE (Mn 115,000, MJMn 1.10). The addition of ethylene/propylene (1 3 volume ratio) to this living PE formed a PE-/>poly(ethylcnc-co-propylcnc) block copolymer (Mn 211,000, MJMn 1.16, propylene content 6.4 mol%) [30], As expected, the polymer exhibits a high Tm of 123 °C, indicating that this block copolymer shows good elastic properties at much higher temperatures than the conventional random copolymers of similar densities. 

Conformational disorder and kink-bands structures have recently been found also in random copolymers of syndiotactic polypropylene with small amounts of ethylene.192 193 The ethylene units are included in the crystalline regions193 and induce the crystallization of the metastable form II of sPP with conformationally disordered chains characterized by kink bands. Portions of chains containing the ethylene units tend, indeed, to assume a trans planar conformation, producing the kink-band defects in chains in the prevailing twofold helical conformation.192193... 

EVA and VAE (see Figure 4.24) are copolymerized from ethylene and vinyl acetate that is randomly distributed along the backbone. The backbone is identical to that of the polyolefins but the pendant groups are different, with a polar character and a random structure that decreases crystallinity the more so as the vinyl acetate level rises. 

Although hdpe and it-PP are crystalline, the commercial random copolymer of ethylene and propylene (EP) is an amorphous elastomer. The most widely used EP copolymer (EPDM) is produced by the copolymerization of ethylene and propylene with a small amount of an alkyldiene this permits cross-linking or vulcanization. 

Single crystals with a Tm of 423 K have been produced from low-density polyethylene (ldpe). Isotactic PP crystals have a Tm of 444 K and syndiotactic PP has a Tm of 411 K, whereas atactic PP is amorphous and has a Ts of 255 K. Isotactic polyolefins with pendant groups, such as polyhexene, have high Tm values. Random copolymers of ethylene and propylene are amorphous, but block copolymers of these monomers are crystalline. 

Because of the geometric regularity present, gutta-percha (/ra/w-polyi-soprene) and stretched NR from Hevea brasitiensis (c/s-polyisoprene) are crystalline. Random copolymers are usually amorphous, but some may be crystalline if the comonomers, such as ethylene and tetrafluoroethylene, are similar in size. Block copolymers may have crystalline domains if either of the com-... 

The poly(ethylene-co-p-methylstyrene) with 10.9 mole % of p-methylstyrene shows a low melting point (76 °C) and very small crystallinity (5.4%), which implies the random distribution of p-methylstyrene along the polyethylene backbone [17]. The detailed sequence distribution can be quantitatively determined by 13C NMR measurements. 

The vinyl fluoride/vinylidene fluoride and the vinyl fluoride/tetra-fluoro ethylene copolymer systems were also studied (21). In the first case isomorphism is observed in the whole range of compositions, while the distribution of the two types of units is random. The crystal structure is that of polyvinyl fluoride, which is virtually identical with one of the three known crystalline forms of polyvinylidene fluoride, and characterized by a planar zig-zag chain conformation. High degrees of crystallinities in the whole range of compositions are also observed in the second case. However, the crystal structure of the two pure homopolymers is not the same hence we are in the presence of isodimorphism. In any case, for vinyl fluoride contents ranging between 0 and 75 mole-% the structure observed is essentially that of polytetrafluoro ethylene in the crystalline... 

To introduce short branches into the otherwise linear polymer, a-olefins are sometimes copolymerized with ethylene. The random branching breaks up the crystallinity of the polymer, imparting more flexibility. In addition to... 

A common example of a copolymer is an ethylene-propylene copolymer. Although both monomers would result in semi-crystalline polymers when polymerized individually, the melting temperature disappears in the randomly distributed copolymer with ratios between 35/65 and 65/35, resulting in an elastomeric material, as shown in Fig. 1.19. In fact, EPDM rubbers are continuously gaining acceptance in industry because of their resistance to weathering. On the other hand, the ethylene-propylene block copolymer maintains a melting temperature for all ethylene/propylene ratios, as shown in Fig. 1.20. 

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