Ethylene monomer

The desired form in homopolymers is the isotactic arrangement (at least 93% is required to give the desired properties). Copolymers have a random arrangement. In block copolymers a secondary reactor is used where active polymer chains can further polymerize to produce segments that use ethylene monomer. 

The overwhelming majority of synthetic polymers is organic in nature, and it is on these that we will concentrate. The simplest and most common synthetic polymer is polyethylene, which will be our first example. Figure 1.1 shows the basic chemical structure of polyethylene. Pairs of hydrogen atoms are attached to the carbon atoms that make up the backbone. The repeat unit in this structure contains two carbon atoms and is derived from the ethylene monomer. In the case of polyethylene, the number of monomer residues, which is known as the polymerization... 

Addition polymers, which are also known as chain growth polymers, make up the bulk of polymers that we encounter in everyday life. This class includes polyethylene, polypropylene, polystyrene, and polyvinyl chloride. Addition polymers are created by the sequential addition of monomers to an active site, as shown schematically in Fig. 1.7 for polyethylene. In this example, an unpaired electron, which forms the active site at the growing end of the chain, attacks the double bond of an adjacent ethylene monomer. The ethylene unit is added to the end of the chain and a free radical is regenerated. Under the right conditions, chain extension will proceed via hundreds of such steps until the supply of monomers is exhausted, the free radical is transferred to another chain, or the active site is quenched. The products of addition polymerization can have a wide range of molecular weights, the distribution of which depends on the relative rates of chain grcnvth, chain transfer, and chain termination. 

A proposed expansion of the corporation s polyethylene production capacity will require additional ethylene monomer as a feedstock. It is suggested that the ethylene be produced by the pyrolysis of a propane stream that is available at axrate of 7000 lb/hr. 

Olefin polymerization catalysts systems typically experience higher reactivity toward ethylene (monomer 1) than LAOs (monomer 2), resulting in I r2 [37], For our purposes, let us consider a hypothetical example where the catalysts have the following reactivity ratios ... 

Polymerization, the reaction of monomer to produce polymer, may be self-polymerization (e.g., ethylene monomer to produce polyethylene), or copolymerization (e.g.,... 

Figure 1.12 Proposed mechanism for conversion of ethylene monomer to dendrigraft polyethylene with Brookhart catalyst at low pressure...

This industrial process remains essentially unchanged from the 1950s [25], Here, a free-radical initiator is added to the ethylene monomer at supercritical conditions (276 MPa and 200-300 °C). The polyethylene remains in the supercritical solution until the pressure is lowered to around 5 MPa, whereupon it precipitates. A range of other monomers can be copolymerized, including carbon monoxide to give polyketones, as shown in Scheme 10.19 [26],... 

Research Focus Synthesis of polymerizable light-absorbing azo dyes useful as intraocular lenses covalently bonded to other unsaturated ethylene monomers. Originality This has been an ongoing 6-year investigation. 

Materials. Polymer-bonded sensitizers and their model compounds are shown in Figure 2. Samples 1-5 were prepared by radical copolymerization of corresponding ethylenic monomers using azobisisobutyronitrile as initiator at 70°C in DMF(5) or DMF/H20 (9/1 for 1, 2 and 4 8/1 for 3) (15). Sample 7 was prepared by the same procedure as 6 (16). The copolymer compositions... 

In particular, EVA waxes refer generally to oligomeric polymer compounds. They are prepared by the copolymerization of ethylene monomers and vinyl acetate monomers in the same way as the high molecular weight types. 

It means that after the incorporation of an ethylene monomer, the addition of propylene is still isospecific. 

The addition polymer polyethylene is formed as electrons from the double bonds of ethylene monomer molecules split away and become unpaired valence electrons. Each unpaired electron then joins with an unpaired electron of a neighboring carbon atom to form a new covalent bond that links two monomer units together. 

As far as the mechanisms of branching and crosslinking are concerned, there appear to us to be certain weaknesses in those commonly accepted. With ethylenic monomers, there can be little doubt that if branching were to occur at all, it will arise from radical attack upon the polymer already formed. It would be immaterial whether this transfer takes place on backbone carbon atoms or via side chains, as is almost certainly true for, say, vinyl acetate. When dienes are present, it has been generally accepted that the residual double bonds are the main seat of reaction, thereby creating the immediate possibility of crosslinking. However, the internal residual double bonds—that is, those... 

Well-defined diblock (P—R) and triblock (P R — P) copolymers consisting of the polypropylene block (P) and the ethylene-propylene random copolymer block (R) were prepared by adding ethylene monomer during the living coordination polymerization of propylene with the soluble V(acac)3/Al(C2H5)2Cl/anisole catalyst U1). 

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