Ethylene polymers description

Olig omerization and Polymerization. Siace an aHyl radical is stable, linear a-olefins are not readily polymerized by free-radical processes such as those employed ia the polymerization of styrene. However, ia the presence of Ziegler-Natta catalysts, these a-olefins can be smoothly converted to copolymers of various descriptions. Addition of higher olefins during polymerization of ethylene is commonly practiced to yield finished polymers with improved physical characteristics. 

Consider the description of the sequence distribution of isotactic and syndiotactic placements in the polymerization of a monosubstituted ethylene. The approach is general and can be applied with appropriate modification to the 1,4-polymerization of a 1,3-diene. Dyad tac-ticity is defined as the fractions of pairs of adjacent repeating units that are isotactic or syndiotactic to one another. The isotactic and syndiotactic dyads (XV) are usually referred to as meso and racemic dyads. The horizontal line in XV represents a segment of the polymer... 

Latexes are usually copolymer systems of two or more monomers, and their total solids content, including polymers, emulsifiers, stabilizers etc. is 40-50% by mass. Most commercially available polymer latexes are based on elastomeric and thermoplastic polymers which form continuous polymer films when dried [88]. The major types of latexes include styrene-butadiene rubber (SBR), ethylene vinyl acetate (EVA), polyacrylic ester (PAE) and epoxy resin (EP) which are available both as emulsions and redispersible powders. They are widely used for bridge deck overlays and patching, as adhesives, and integral waterproofers. A brief description of the main types in current use is as follows [87]. 

For those familiar with polymer chemistry, polyurethane may be a confusing term. Unlike polyethylene, the polymerization product of ethylene, a polyurethane is not the result of the polymerization of urethane. To add to the confusion, a urethane is a specific chemical bond that comprises a very small percentage of the bonds of a polyurethane. Since we are interested in chemical and physical effects, polyether or polyester is a more descriptive term for the most common bond in a polyurethane. Despite this complication, it is instructive to begin by talking about the methane bond from which the polyurethane name is derived. The general structure or bond that forms the basis of this chemistry is the urethane linkage shown in Figure 2.1. 

According to descriptions published by the Thiokol Chemical Corporation [9] and Gobel [10] liquid thiokol is obtained in the following way ethylene chloro-hydrin is condensed into dichlorodiethylformal (I) which is then treated with sodium polysulphide to form the polymer (II) ... 

Description Polymer-grade ethylene is oligomerized in the liquid-phase reactor (1) with a catalyst/solvent system designed for high activity and selectivity. Liquid effluent and spent catalyst are then separated (2) the liquid is distilled (3) for recycling unreacted ethylene to the reactor, then fractionated (4) into high-purity alpha-olefins. Spent catalyst is treated to remove volatile hydrocarbons and recovered. The table below illustrates the superior purities attainable (wt%) with the Alpha-Select process ... 

Description Liquid or gaseous ethylene is fed, together with a solvent and required comonomer(s) into a stirred, liquid-filled, vessel-type reactor (1). The reactor is operated adiabatically thus, the feed is precooled. All heat of reaction is used to raise polymerization temperature up to approximately 200°C. Hydrogen is used to control polymer molecular weight. A high-activity, proprietaiy catalyst is prepared onsite from commercially available components. Ethylene... 

We begin with a description of the high-pressure polymerization process since it is an authentic example of how the principles of thermodynamics and kinetics can be combined with creative engineering to develop an economically viable high-pressure process. These principles can be generalized and extended to other high-pressure processes. After describing the polyethylene process, we move on to more recent work on polyethylene and ethylene copolymers, followed by a discussion of other recent SCF studies with a variety of other polymers and monomers. 

The informadon from this example tells us that 21,500 molecular weight polymer does not dissolve completely in ethylene, and a top phase and a bottom phase are formed. When the vessel is cooled (by the blast of cold air), both the phases are, of course, cooled. The example does not say if during the subsequent ethylene blowdown step any polyethylene escapes. However, at the cooled condidons, polyethylene solubility in ethylene is virtually nil and, therefore, we suggest that the aggregates of polyethylene are formed during the cooling step. The description of the polyethylene at the bottom of the vessel as a fused mass indicates that most of the ethylene had left the polyethylene before it solidified. 

Yoshimura et al. [1989] give a lengthy description of their invention, which was primarily aimed at producing film (Table 11.9) particularly suited for shrink wrapping, with many examples and extensive sets of results. The film is made from the following three groups of polymers (i) LDPE and a copolymer of ethylene, either with vinyl ester monomer, or with an unsaturated aliphatic monocarboxylic acid or its aliphatic ester (EVAc being the most desirable copolymer) (ii) one of the... 

Description Polymer-grade ethylene is oligomerized in a liquid-phase reactor (1) with a homogeneous liquid system that has high activity and selectivity. 

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