Very-low-density polyethylenes

This material, with a density down to 0.88 Mg m , is believed to be a copolymer of ethylene with a higher olefin. No pattern of applications seems to have been established. 

We can vary the density of very low density polyethylene from 0.90 down to 0.86 g/cm by varying the comonomer level from approximately 8 to 14 mole %. At the highest comonomer levels, crystallization is impeded by the branches to such an extent that only about 5% of the material crystallizes. The crystallites of very low density polyethylene are small and poorly organized. We polymerize these resins usii single-site catalysts, which give us relatively narrow molecular weight and composition distributions 

Very low density polyetiiylenes are relatively soft and transparent, because they are largely noncrystalline in nature. Films made from these materials are resilient with a moderate level of elastic recovery, as long as they are not stretched beyond strain levels of approximately 100%. At their lower densities, they feel tacky and tend to stick to each other. We often blend very low density polyethylene into higher density grades of polyethylene or isotactic polypropylene to boost their impact resistance. 

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At the end of the 1970s considerable interest developed in what became known as linear low density polyethylenes (LLDPE) which are intermediate in properties and structure to the high pressure and low pressure materials. While strictly speaking these are copolymers it is most convenient to consider them alongside the homopolymers. The LLDPE materials were rapidly accepted by industry particularly in the manufacture of film. The very low density polyethylenes (VLDPE) introduced by Union Carbide in 1985 were closely related. 

Metallocene-catalysed very low density polyethylene (m-VLDPE) has become available with densities of as low as 0.903. This is of use for sealing layers of multi-layer films since sealing can commence at lower temperatures than with conventional materials such as LLDPE and EVA (see Section 11.6) with the polymer seal exhibiting both cold strength and hot tack strength. 

Figure 18,2 d) illustrates the general structure of very low density polyethylene, which we also call ultra low density polyethylene. In common with linear low density polyethylene, these resins are copolymers of ethylene and 1-alkenes. The comonomer level ranges from approximately 8 to 14 mole %. We normally refer to these polymers as VLDPE or ULDPE. The molecules of very low density polyethylene contain a distribution of lengths and branch placements. 

We make polyethylene resins using two basic types of chain growth reaction free radical polymerization and coordination catalysis. We use free radical polymerization to make low density polyethylene, ethylene-vinyl ester copolymers, and the ethylene-acrylic acid copolymer precursors for ethylene ionomers. We employ coordination catalysts to make high density polyethylene, linear low density polyethylene, and very low density polyethylene. 

To demonstrate this technology, we targeted a copolymer with blocks of both high density polyethylene (HDPE, density 0.94 g cm 3) and very low density polyethylene (VLDPE, density -0.88 g cm 3). Process and product characterization details are given in Table 6. We chose the pyridylamide precatalyst 18 [41] for this study due to its high comonomer reactivity, high M°, and demonstrated CCTP ability. 

Plastomers is the name given to copolymers of ethylene that have a little crystallinity, but are largely amorphous. They are also called very low-density polyethylene (VLDPE). They are more elastic than LLDPE but less stiff. They are used as a sealing layer in film applications and controlled permeation packaging for vegetables and fruits. 

PS PSF PSU PTFE PU PUR PVA PVAL PVB PVC PVCA PVDA PVDC PVDF PVF PVOH SAN SB SBC SBR SMA SMC TA TDI TEFE TPA UF ULDPE UP UR VLDPE ZNC Polystyrene Polysulfone (also PSU) Polysulfone (also PSF) Polytetrafluoroethylene Polyurethane Polyurethane Poly(vinyl acetate) Poly(vinyl alcohol) poly(vinyl butyrate) Poly(vinyl chloride) Poly(vinyl chloride-acetate) Poly(vinylidene acetate) Poly(vinylidene chloride) Poly(vinylidene fluoride) Poly(vinyl fluoride) Poly(vinyl alcohol) Styrene-acrylonitrile copolymer Styrene-butadiene copolymer Styrene block copolymer Styrene butadiene rubber Styrene-maleic anhydride (also SMC) Styrene-maleic anhydride (also SMA) Terephthalic acid (also TPA) Toluene diisocyanate Ethylene-tetrafluoroethylene copolymer Terephthalic acid (also TA) Urea formaldehyde Ultralow-density polyethylene Unsaturated polyester resin Urethane Very low-density polyethylene Ziegler-Natta catalyst... 

Application To produce linear polyethylene from very low density polyethylene (VLDPE) to linear low density polyethylene (LLDPE) to high density polyethylene (HDPE) and other specialty types using the Spherilene gas-phase technology and a single Ziegler-Natta titanium-based catalysts family. 

Also worthy of mention are the new very-low-density polyethylenes (VLDPEs), which are produced using metallocene-based catalysts [9]. These materials, which remain largely experimental at the moment, have a density of less than 0.9g/cm. ... 

Polypropylenes are subdivided to homopolymers and copolymers. Homopolymers are more crystalline, have a rather well-defined melting temperature at 161-165°C (322-329°F), softens at about 155°C (311°F), and have a rather narrow molecular weight distribution. Copolymers typically contain some amount of ethylene comonomer and in turn are subdivided to random and block copolymers. Their melting points are in the range of 140-155°C (284-311°F). Polypropylenes have a specific gravity (density) of 0.90-0.91 g/cm which is approximately equal to that of very low-density polyethylene and lower than that of majority of polyethylenes, particularly HDPE (0.941-0.965 g/cm ). PP homopolymers are stiffer than copolymers, with their flexural modulus of 165,000-290,000 psi and 130,000-175,000 psi, respectively. PP homopolymers, in turn, are generally stiffer compared to HDPE, which has flex modulus in the range of 125,000-... 

PEMA Polyethylmethacrylate VLDPE Very low density polyethylene... 

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