Butene-1/ethylene, copolymerization

The copolymerization of ethylene with other olefins is affected by the variation of the Al Zr ratio, temperature, and catalyst concentration. These variables lead to changes in the molecular weight and the ethylene content. Higher temperatures lead to increases in the ethylene content and low molecular weights. Investigations of ethylene copolymerization with 1-butene... 

Chain propagation of CO/ethylene copolymerization proceeds by a strictly alternating insertion of CO and olefin monomers in the growing chain. It is safe to assume that double CO insertion does not occur for thermodynamic reasons [Ic]. However, the complete absence of double ethylene insertions is remarkable because ethylene insertion in a Pd-alkyl species must be exothermic by about 20 kcal/mol (84 kJ mol). The observation of strict alternation is the more surprising since the same palladium catalysts also efficiently dimerize ethylene to butenes [25]. The perfect alternation is maintained even in the presence of very low concentrations of carbon monoxide. When starting abatch polymerization at a high ethylene/CO ratio, error-free copolymer is produced until all the CO is consumed then the system starts forming butenes (with some catalyst systems at about twice the rate of copolymerization ). 

The development of bifunctional catalysts for specific catalytic sequences of reactions in which the product of the first reaction can serve as substrate for the second is of great importance. There are many examples of such reactions. They are, for instance, the monomer-isomerizing polymerization of heptene-2, heptene-3 and 4-methyl-2-pentene and the combination of propene disproportionation with oligomerization, etc. Bifunctional catalysts are most widely used for ethylene copolymerization with a-butene in situ in the production of so-called low-density linear polyethylene (LDLPE). All general methods for LDLPE production are based on incorporation into a PE backbone of short-chain branches, which can be made by catalytic copolymerization of ethylene with a-olefins C3-C10. A macromolecnlar ligand offers wide possibilities of joining the different types of active site in the same matrix (see also Section 12.5.2). 

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. 

It is well known that the usual Ziegler-Natta catalysts do not directly polymerize -olefins but that they can copolymerize them with some a-olefins. A good example of this phenomenon is the ethylene-butene-2 copolymerization, which has been thoroughly studied (13). The butene-2 content of the copolymers was measured radiochemically or by the IR method with the 1380 cm band. The absence of significant isomerization of butene-2 to butene-1 was proved by the absence from the copolymer spectra of the 773 cm band (ethyl branching). 

However, Natta and coworkers 25—27) reported that ethylene copolymerized with butene-2 without isomerization and with cydopentene in the presence of Al(hexyl)3/YCl4 or AIEt2Cl/V(acac)3 catalyst to alternating structures (Eqs. 3 and 4) at sufficiently low ethylene concentratiem at -30 C ... 

Novel polyethylene materials have been synthesized by copolymerization of ethylene with 1-butene, 1-hexene, and/or 1-octene using metallocene catalyst systems [9]. 

Copolymerization e.g., of 1-butene or 1-hexene with ethylene, gives short-chain branching-, e.g., the branches contain three or five carbon atoms. The random location of the side-chains lowers the crystallinity and density. Long-chain branching refers to branches that are similar in length to the polymer backbone and this type occurs in polyethylene manufactured using the... 

It has been shown by Barb and by Dainton and Ivin that a 1 1 complex formed from the unsaturated monomer (n-butene or styrene) and sulfur dioxide, and not the latter alone, figures as the comonomer reactant in vinyl monomer-sulfur dioxide polymerizations. Thus the copolymer composition may be interpreted by assuming that this complex copolymerizes with the olefin, or unsaturated monomer. The copolymerization of ethylene and carbon monoxide may similarly involve a 1 1 complex (Barb, 1953). 

The sterically unencumbered catalyst active site allows the copolymerization of a wide variety of olefins with ethylene. Conventional heterogeneous Ziegler/Natta catalysts as well as most metallocene catalysts are much more reactive to ethylene than higher olefins. With constrained geometry catalysts, a-olefins such as propylene, butene, hexene, and octene are readily incorporated in large amounts. The kinetic reactivity ratio, rl, is approximately... 

The monomers used to make an addition polymer need not be identical. When two or more different monomers are polymerized into the same chain, the product is a copolymer. For instance, we routinely copolymerize ethylene with small percentages of other monomers such as a-olefins (e.g., 1-butene and 1-hexene) and vinyl acetate. We call the products of these reactions linear low density polyethylenes and ethylene-vinyl acetate copolymer, respectively. We encounter these copolymers in such diverse applications as cling film, food storage containers, natural gas distribution pipes, and shoe insoles. 

We can incorporate short chain branches into polymers by copolymerizing two or more comonomers. When we apply this method to addition copolymers, the branch is derived from a monomer that contains a terminal vinyl group that can be incorporated into the growing chain. The most common family of this type is the linear low density polyethylenes, which incorporate 1-butene, 1-hexene, or 1-octene to yield ethyl, butyl, or hexyl branches, respectively. Other common examples include ethylene-vinyl acetate and ethylene-acrylic acid copolymers. Figure 5.10 shows examples of these branches. 

The ethylene-1-butene block cannot be obtained directly since the two monomers do not undergo anionic copolymerization. 

Certain half-sandwich phenoxides have been shown to be highly active olefin polymerization catalysts. For example, the zirconium complex (60) polymerizes ethylene with an activity of 1,220 gmmol-1 h-1 bar-1.181 A similar titanium complex (61) displays an activity of 560gmmol ll bar 1 at 60°C.182-189 Comparable activities were also recorded for the copolymerization of ethylene with 1-butene and 1-hexene. 

Ethylene-1-butene copolymers, 20 180 Ethylene-1-olefin copolymerization, 26 525 Ethylene-acrylic elastomers, 10 696-703 commercial forms of, 10 697-698 dynamic mechanical properties of,... 

Statistical copolymerization occurs among ethylene and various a-olefins [Baldwin and Ver Strate, 1972 Cooper, 1976 Pasquon et al., 1967 Randall, 1978]. The reactivities of monomers in copolymerization generally parallel their homopolymerization behavior ethylene > propene > 1-butene > 1-hexene [Soga et al., 1989]. Table 8-7 shows monomer reactivity ratios for several comonomer pairs. 

Coordination copolymerization of ethylene with small amounts of an a-olefin such as 1-butene, 1-hexene, or 1-octene results in the equivalent of the branched, low-density polyethylene produced by radical polymerization. The polyethylene, referred to as linear low-density polyethylene (LLDPE), has controlled amounts of ethyl, n-butyl, and n-hexyl branches, respectively. Copolymerization with propene, 4-methyl-1-pentene, and cycloalk-enes is also practiced. There was little effort to commercialize linear low-density polyethylene (LLDPE) until 1978, when gas-phase technology made the economics of the process very competitive with the high-pressure radical polymerization process [James, 1986]. The expansion of this technology was rapid. The utility of the LLDPE process Emits the need to build new high-pressure plants. New capacity for LDPE has usually involved new plants for the low-pressure gas-phase process, which allows the production of HDPE and LLDPE as well as polypropene. The production of LLDPE in the United States in 2001 was about 8 billion pounds, the same as the production of LDPE. Overall, HDPE and LLDPE, produced by coordination polymerization, comprise two-thirds of all polyethylenes. 

Because of its commercial importance, the polymerization of ethylene at high pressure has been extensively studied.204-209 Free-radical polymerization is characteristic of ethylene and vinyl compounds. Simple alkenes, such as 1-butene, however, do not give high-molecular-weight polymers, but they, as well as internal alkenes, can copolymerize with polymerizable monomers. 

Linear low-density polyethylene (LLDPE)440-442 is a copolymer of ethylene and a terminal alkene with improved physical properties as compared to LDPE. The practically most important copolymer is made with propylene, but 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are also employed.440 LLDPE is characterized by linear chains without long-chain branches. Short-chain branches result from the terminal alkene comonomer. Copolymer content and distribution as well as branch length introduced permit to control the properties of the copolymer formed. Improvement of certain physical properties (toughness, tensile strength, melt index, elongation characteristics) directly connected to the type of terminal alkene used can be achieved with copolymerization.442... 

The selective orientation may indicate a steric hindrance from the branch. Internal olefins like 2-butene tend to be poisons. They adsorb strongly but do not copolymerize to any significant extent. 2-Methylpropene is not very reactive either. In the absence of ethylene, a-olefins can be polymerized over Cr/silica but their reactivity is much lower than that of ethylene. Sometimes adding a-olefins to the reactor will improve activity, not because they are more reactive monomers, but because they are better reducing agents. 

HDPE is alinear polymer with the chemical composition ofpolymethylene, (CII2V Depending on application, HDPE molecules either have no branches at all. as in certain injection molding and blow molding grades, or contain a small number of branches which are introduced by copolymerizing ethylene with o-olefins, e g., ethyl branches in the case of 1-butene and -butyl branches in the case of 1-hexene. The number of branches in HDPE resins is low, at most 5 to 10 branches per 1000 carbon atoms in the chain. 

There is a large market for LLDPE produced by the copolymerization of ethylene and an -olefin, usually containing 1-butene, 1-hexene, or 1-octene. The density for LLDPE is between 0.915 and 0.925 kg/liter, whereas HDPE has a density of 0.960 kg/liter and LDPE a density of 0.91-0.93 kg/liter. 

At present, problems relating to immobilized complexes treated as models of polyfunctional catalysts are being extensively studied. It is assumed that such systems will allow us to realize consecutive reactions in such a way that the product of one of them will serve as a substrate for the next reaction. In optimal conditions this would make it possible to effect in a single reactor a number of conversions to obtain final products with minimum power and material expenditure [133]. This process can be exemplified by copolymerization of ethylene with butene-1 which appears on bifunctional immobilized heterometallic catalysts [22c]. 

Butene-1 can be copolymerized with ethylene as well as higher a-olefins like propylene and 4-methyl-pentane. 

Copolymers may also be produced with a catalyst containing both chromium oxide and nickel oxide supported on silica-alumina. It is well-known that nickel oxide—silica—alumina by itself makes predominantly butenes from ethylene. In the mixed catalyst, butenes that are formed on nickel oxide copolymerize with ethylene on the chromium oxide to form ethylene-butene copolymers. The fact that infrared shows only ethyl branching in the polymer indicates that the initial product... 

Under a process that consisted in copolymerizing in the existing highpressure installation ethylene with 5 to 10 percent of an a-olefin (butene-1, hexene-1), a stronger linear low-density polyethylene (LLDPE) was produced with a higher melting point than LDPE. Thinner films could thus be produced that were just as strong but required less material. 

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