Polyethylene differences

One of the mam uses of the linear a olefins prepared by oligomerization of ethylene is in the preparation of linear low density polyethylene Linear low density polyethylene is a copoly mer produced when ethylene is polymerized in the presence of a linear a olefin such as 1 decene [H2C=CH(CH2)7CH3] 1 Decene replaces ethylene at random points in the growing polymer chain Can you deduce how the structure of linear low density polyethylene differs from a linear chain of CH2 units ... 

Substituents on the a-carbon atom restrict chain flexibility but, being relatively small, lead to a significantly higher Tg than with polyethylene. Differences in the Tg s of commercial polymers (approx. 104°C), syndiotactic polymers (approx. 115°C) and anionically prepared isotactic polymers (45°C) are generally ascribed to the differences in intermolecular dipole forces acting through the polar groups. 

The two forms of polyethylene differ slightly in density. Linear polyethylene is referred to in the recycling business as /ligh-density polyethylene, represented by the symbol HDPE 2 on the bottom of a plastic bottle. The corresponding symbol for branched polyethylene is LDPE 4, indicating low-density polyethylene. (The smaller the number, the easier it is to recycle.)... 

Why do the enthalpy diagrams for the melting of indium and low density polyethylene differ from one another What does the breadth of the melting peak tell us about the polymer under study ... 

In polymers there are microregions undergoing reactions different from those occurring in the neighbouring material when exposed to radiation. For example, the crosslinking behaviour In amorphous polyethylene differs from that in the crystalline phase... 

In the previous sections, we have discussed linear polyethylene samples that were prepared under different conditions. The polymers, called polyethylene, differ widely in molecular structure, i.e. in molecular weight and its distribution, exis-... 

Pure polyethylene should not absorb ultraviolet radiation of wavelength above 200 nm since pure paraffins are transparent in that region of the spectrum. However, it is well established [ 20] that even carefully purified polyethylene differs from a simple high molecular weight straight chain paraffin in being to some extent unsaturated. The total unsaturation has been estimated to be about 0.25% C=C by weight [21]. Olefinic unsaturation of different types has been detected by infrared spectroscopy [21, 22] it seems to be mainly of the vinyl type in linear polyethylene, while most unsaturation is of the vinylidene type in branched polyethylene [22]. Attention has also been drawn to the fact that a structure seems to be present in low density polyethylene which leads to a triene on ultraviolet irradiation [23]. 

High-pressure polyethylene differs from polyethylene, made with the aid of Ziegler catalysts, in having a lower density and lower T. It has been suggested that this is due... 

The Sclair resins under study here were of similar melt index and were manufactured under similar conditions. They are a uniform series of polyethylenes differing only in density. Microscopic observation under polarized light confirmed the hypothesis that the higher crystallinity in... 

Flow do molecules of low-density polyethylene and high-density polyethylene differ How do these molecular scale differences explain the differences in the macroscopic properties of these materials ... 

Comparison of the specific retention volumes of hydrocarbons on poly-dimethylsiloxane [10], determined in two different laboratories by two groups of researchers over the temperature range 25—55°C differ by 3—5%. Similarly the determination of retention of n-decane and n-do-decane on linear polyethylene differs by 8% [11,12]. Braun et al. [12] determined the amount of polymer remaining after calcination and found that the support loses 0.2% of weight on drying and 0.46% on calcination. The application of corrections to the results obtained in reference [11] has improved the agreement however the discrepancy depends on the content of stationary phase for 5—6% stationary phase the difference is 7.5%, while for 10—11% it drops to 3.6%. The value determined for the content of stationary phase depends on the method, and so does the value of Vg Table 2.3 shows the difference between the concentra-... 

Polymers are obviously different from small molecules. How does polyethylene differ from oil, grease, and wax, all of these materials being essentially —CH2— ... 

The various types of polyethylene differ in molecular structure, crystallinity, molecular weight, and molecular weight distribution. 

Fig. 11 Dependence of the steady-state tensile viscosity riE on the tensile stress at 150°C for three metallocene-catalyzed polyethylenes differing in branching topology. Curves are fitted to the data points to guide the eye. Reprinted from [120], with kind permission from American Chemical Society.

For example, prior to the discovery of this new single-site catalyst type, commercial grades of polyethylene were primarily manufactured over the compositional range of 0-4 mol% of comonomer (1-butene, 1-hexene or 1 -octene) that provided ethylene copolymers over the density range of 0.915-0.970 g/cc. Commercial catalysts were primarily the Cr-based Phillips-type of catalyst or a Ti-based Ziegler catalyst with the xmderstand-ing that both types of catalyst consisted of many different types of active sites. Each type of active site produced a different composition of polyethylene (different molecular weight and branching content) which resulted in a final polyethylene material with a complex molecular structure. These multi-site catalysts limited the composition of the polyethylene that was commercially available due to both process and product constraints imposed by such catalysts. 

The window of miscibility in this case is an ellipse contained within the boundaries of the copolymer composition map. Additional examples of the mean field approach to predict the miscibility window for cop olymer-copolymer blends include SAN/SMMA, SMMA/MMA-AN and SAN/MMA-AN [188], amSAN/SAN and amSAN/SMA [202], SMMA/SMMA (different compositions) [203 ], SMA/tetramethyl Bis A polycarbonate [204], chlorinated PVC (different compositions), chlorinated polyethylene (different compositions and MMA-EMA (different compositions) [177] and SAN/NBR [205]. This approach has also been applied to ternary blends of PPO/PS/poly(o-chlorostyrene-co-p-chlorostyrene) [206]. The mean field binary interaction model approach was also successfully applied to polyamides based on various combinations of aliphatic and aromatic units [207]. 

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