Polyethylene modeling copolymerization

More industrial polyethylene copolymers were modeled using the same method of ADMET polymerization followed by hydrogenation using catalyst residue. Copolymers of ethylene-styrene, ethylene-vinyl chloride, and ethylene-acrylate were prepared to examine the effect of incorporation of available vinyl monomer feed stocks into polyethylene [81]. Previously prepared ADMET model copolymers include ethylene-co-carbon monoxide, ethylene-co-carbon dioxide, and ethylene-co-vinyl alcohol [82,83]. In most cases,these copolymers are unattainable by traditional chain polymerization chemistry, but a recent report has revealed a highly active Ni catalyst that can successfully copolymerize ethylene with some functionalized monomers [84]. Although catalyst advances are proving more and more useful in novel polymer synthesis, poor structure control and reactivity ratio considerations are still problematic in chain polymerization chemistry. 

Copolymerization with a-olefins over a Phillips catalyst is a key method for controlling the density and microstmctures of the polyethylene products in industrial processes. Table 5 also listed the energy barriers for the primary 1,2-insertion of 1-butene and 1-hexene, and the subsequent chain transfer by p-H elimination for all the three kinds of Ti-modified models. The calculated energy barriers showed that Ti-modification could also promote the activity for ethylene copolymerization with a-olefins. The energy differences between comonomer insertion and chain transfer can lead to a conclusion on the effect of Ti-modification on the distribution of the inserted comonomers in polyethylene chains. As listed in Table 5, the difference between energy barriers for chain propagation and for chain transfer decreased for model sites 4g, 12g, and 15g. Therefore, it was reasonable to conclude that Ti-modified catalyst was likely to make low MW polyethylene with much less comonomer insertion because the inserted comonomer mainly led to a chain transfer reaction and left the inserted comonomer at the chain end. As a result, the increased chain termination by comonomer resulted in less SCBs in the low MW fraction and higher density of the polyethylene product for the Ti-modified Phillips catalyst. 

NIR has been used to monitor the polymerization of acrylic acid [4], for the solution polymerization of methyl methacrylate (MMA) in toluene [5], for following the emulsion polymerization of MMA and butyl acrylate [6], and for monitoring the copolymerization of MMA and N,N-dimethylacrylamide (Figure 20.2) [33]. The density of linear low-density polyethylene was monitored using NIR and a partial least-squares (PLS) calibration model [7]. 

Due to its practical importance as a cable material and due to its special position as a model polymer, polyethylene has been the subject of numerous dielectric studies. In coimnon with poly(vinylidene fluoride), polyethylene shows a complicated relaxation behaviour. Since the chain is intrinsically non-dipolar the material is oxidized, dil( inated or is made by copolymerizing carbon monoxide with ethylene, so that d les can be introduced to act as a probe on the motions of the parent material. Extensive accounts of the eady eiqjerimental wodc are available (McCrum et al.,... 

Absent from Table 10 are the comonomers carbon monoxide, carbon dioxide, and sulfur dioxide. These comonomers are not included because their copol mieiization does not obey the normal copolymer model illustrated by reactions (vix—xvii) and hence cannot be described by kinetic parameters which take into account only these reactions. For example. Furrow (/28) has i own that caibon dioxide will react with growing polyethylene chains in a free-radical reaction, but that it terminates the chains giving carboxylic acids. It does not copolymerize in the usual sense (which would give polyesters). Carbon monoxide and sulfur dioxide appear not to obey the normal cppol3nner curve of feed composition versus polymer composition and it has been reported that these materials form a complex with ethylene whidi is more reactive than free CO or SOg, perhaps a 1 1 complex. Copolymerization of both CO and SO is further complicated by a ceiling temperature effect. Cppolymerization has been carried out with ethylene and these monomers, however, and poly-ketones and pol3Tsufones are the resultant products. 

Keep in mind that the conceptual models of polymer structure illustrated in Figures 1.2 and 1.3 have been highly simplified. For example, it is possible for a copolymer to have a wide range of substructural elements giving rise to an impressive range of possibilities. In industrial practice, polyethylenes, including UHMWPE, are frequently copolymerized with other monomers (e.g., polypropylene) to achieve improved processing characteristics... 

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