Copolymerisation with ethylene

By copolymerising with a small amount of second monomer which acts as an obstruction to the unzipping reaction, in the event of this being allowed to start. On the industrial scale methyl methacrylate is sometimes copolymerised with a small amount of ethyl acrylate, and formaldehyde copolymerised with ethylene oxide or 1,3-dioxolane for this very reason. 

Many monomers have been copolymerised with ethylene using a variety of polymerisation systems, in some cases leading to commercial products. Copolymerisation of ethylene with other olefins leads to hydrocarbon polymers with reduced regularity and hence lower density, inferior mechanical properties, lower softening point and lower brittle point. 

Incorporation of flexible aliphatic links, for example by copolymerising with ethylene glycol. 

The different reactivities of the olefins are important for the copolymerisation. The comonomer reactivity ratio, rj, in copolymerisation with ethylene appears to decrease with increasing steric hindrance around the double bond in the a-olefin in to the following order [250] ethylene > propylene > 1-butene > linear a-olefin > branched a-olefin. 

The ability of a /i-olefin to copolymerise with ethylene in the presence of Ziegler-Natta catalysts arises from minimisation of steric interactions at the catalytic active site by ethylene units the steric hindrance, which prevents homopropagation of the /1-olefin, is overcome when the /<-olefin monomer is... 

Cycloolefins having rings with more than four carbon atoms do not homo-polymerise in the presence of Ziegler-Natta catalysts based on titanium or vanadium compounds as precursors and alkylaluminium activators. However, these cycloolefins may copolymerise with ethylene via the double bonds while preserving the cycloolefin ring ethylene is able to compensate the steric hindrance at the Ca atom of the growing chain after and before the 1,2-insertion of the cycloolefin [2],... 

Functionalised a-olefins capable of undergoing insertion polymerisation with Ziegler-Natta catalysts are, in principle, monomers in which the heteroatom (X) does not electronically interact with the double bond to be polymerised in such monomers, the heteroatom is separated from the double bond CH2=CH-(CH2)x X [326,384,518,522-528], Monomers with the heteroatom directly bound to the double bond, i.e. those of the CH2=CH-X type, may also undergo polymerization, but when the heteroatom is silicon or tin (X= Si, Sn) [522-526], Representative examples of the insertion polymerisation of functionalised a-olefins and their copolymerisation with ethylene and a-olefins in the presence of heterogeneous Ziegler-Natta catalysts are shown in Table 3.7 [2,241,326,384,518,522-528],... 

How can one explain the occurrence of steric defects in tactic poly(ot-olefin)s Explain why high-resolution nuclear magnetic resonance is the most convenient method for determining the chain micro structure in poly(a-olefin)s. Consider how 3H and 13C NMR spectroscopy can provide stereochemical information concerning a-olefin polymer chains on the diad level (m, r) and the triad level (mm, rr, mr). Explain why /1-olefins, which do not homopolymerise (without isomerisation) in the presence of Ziegler-Natta catalysts, undergo copolymerisation with ethylene in the presence of these catalysts. 

Styrene undergoes copolymerisation with ethylene and various a-olefins in the presence of heterogeneous Ziegler-Natta catalysts. Its reactivity in the copolymerisation is quite low, which is illustrated by the values of the relative reactivity ratios, r and r2, presented in Table 4.5 [118]. One may note, however, a considerably high relative reactivity of styrene in copolymerisation with vinyl-cyclohexane. The copolymerisation of styrene with small amounts of a-olefin, such as 1-octene or 1-decene, yields copolymers of reduced crystallinity and thus reduced brittleness compared with the homopolymer of styrene. 

Ethylene has also been trimerized selectively to 1-hexene, used as a monomer for copolymerisation with ethylene (Chapter 7). 

Polypropylene is somewhat similar to HDPE in general properties. It exists as a homopolymer and a copolymer with ethylene and other hydrocarbons. It can also be blended with polyisobutylene. PP is one of the lowest density plastics, translucent to natural milky white with a highly crystalline structure. PP homopolymer has poor low-temperature resistance but this has largely been overcome by copolymerisation with ethylene. 

PP homopolymer is copolymerised with ethylene. In block copolymers, the ethylene content is much higher than the random copolymers. The copolymerised part of the material is rubbery and forms a separate dispersed phase within the PP matrix. As a result, block copolymerised PP is much tougher than homopolymerised PP and can withstand higher impact even at low temperatures but at the expense of transparency and softening point. The main applications of the block copolymerised PP are similar to those of elastomer-modified PP but where the impact property requirement is not that critical. 

Polypropylene, unlike the polyethylenes, is not subject to environmental stress cracking, which gives it an advantage in the food packaging field. It also has a lower density (0.90 g/cm ) than either LDPE or HOPE. Although the impact strength of polypropylene is lower than that of HOPE, especially at temperatures below 0 °C, this can be improved by incorporating various synthetic rubbers into polypropylene or by copolymerisation with ethylene and propylene. 

Dow catalysts have a high capabihty to copolymetize linear a-olefias with ethylene. As a result, when these catalysts are used in solution-type polymerisation reactions, they also copolymerise ethylene with polymer molecules containing vinyl double bonds at their ends. This autocopolymerisation reaction is able to produce LLDPE molecules with long-chain branches that exhibit some beneficial processing properties (1,2,38,39). Distinct from other catalyst systems, Dow catalysts can also copolymerise ethylene with styrene and hindered olefins (40). 

AH higher a-olefins, in the presence of Ziegler-Natta catalysts, can easily copolymerise both with other a-olefins and with ethylene (51,59). In these reactions, higher a-olefins are all less reactive than ethylene and propylene (41). Their reactivities in the copolymerisation reactions depend on the sise and the branching degree of their alkyl groups (51) (see Olefin polya rs, linear low density polyethylene). 

Ethylene has also been copolymerised with a number of non-olefinic monomers and of the copolymers produced those with vinyl acetate have so far proved the most significant commercially . The presence of vinyl acetate residues in the chain reduces the polymer regularity and hence by the vinyl acetate content the amount of crystallinity may be controlled. Copolymers based on 45% vinyl acetate are rubbery and may be vulcanised with peroxides. They are commercially available (Levapren). Copolymers with about 30% vinyl acetate residues (Elvax-Du Pont) are flexible resins soluble in toluene and benezene at room temperature and with a tensile strength of about lOOOlbf/in (6.9 MPa) and a density of about 0.95 g/cm. Their main uses are as wax additives and as adhesive ingredients. 

As already mentioned in previous sections ethylene may also be copolymerised with several non-hydrocarbon polymers. Some of these copolymers are elastomeric and they also have a measure of oil resistance. Two monomers used commercially are vinyl acetate and, the structurally very similar, methyl acrylate ... 

If ethylene is copolymerised with vinyl acetate, and the vinyl acetate component hydrolysed to vinyl alcohol, a material is produced which is in effect a copolymer of ethylene and vinyl alcohol. 

A stereo specific polymer produced by the copolymerisation of ethylene and propylene with Ziegler-type catalysts. 

The copolymerisation of ethylene with vinyl acetate (VA) is another method by which the crystallinity of polyethylene can be reduced and a rubbery polymer obtained. The final properties of the copolymer depend on the VA content at a VA level of 50% the copolymer is entirely amorphous, and elastomeric grades generally contain 40-60% VA by weight. The oil resistance of the copolymer is also dependent on the VA content in general, however, this lies between that of SBR and polychloroprene. It is swollen by most organic solvents and not resistant to animal and vegetable oils, but has some resistance to weak acids and alkalis at ambient temperature. 

Ethylene can be copolymerised with several monomers like propylene, 1-butene, vinyl acetate, ethyl acrylate, etc. 

Insite technology from Dow Chemical has enabled the production of ethyl ethylene-styrene interpolymers (ESI) by copolymerisation of ethylene and styrene monomers. The properties of interpolymers vary significantly with copolymer styrene content. Interpolymers with up to about 45 wt.% copolymer styrene are semi-crystalline and exhibit good low temperature toughness. Interpolymers with greater than about 45 wt.% copolymer styrene are... 

The same group of coordination polymerisations in which alkene undergoes re complex formation with the metal atom includes the copolymerisation of ethylene, a-olefins, cycloolefins and styrene with carbon monoxide in the presence of transition metal-based catalysts [54-58], In this case, however, the carbon monoxide comonomer is complexed with the transition metal via the carbon atom. Coordination bond formation involves the overlapping of the carbon monoxide weakly antibonding and localised mostly at the carbon atom a orbital (electron pair at the carbon atom) with the unoccupied hybridised metal orbitals and the overlapping of the filled metal dz orbitals with the carbon monoxide re -antibonding orbital (re-donor re bond) [59], The carbon monoxide coordination with the transition metal is shown in Figure 2.2. 

Coordination catalysts allowed for the first time the copolymerisation of ethylene with other olefins such as 1-butene, 1-hexene or 1-octene, which, by introducing side branches, reduces the crystallinity and allows a linear low-density polyethylene to be produced at comparatively low pressures [136], Figure 2.3 shows schematic structures for the three polyethylenes, with the main features exaggerated for emphasis [46]. 

The use of coordination catalysts, especially homogeneous vanadium-based catalysts, for the copolymerisation of ethylene and propylene, with an ethylene content of 15-75 mol.-% in the feed, made it possible to produce amorphous... 

The polymerisation of ethylene in the presence of an Ni(II) complex containing a ligand originating from aminobis(imino)phosphorane leads to short-chain branched polyethylene [182]. This is due to the copolymerisation of ethylene with short-chain 1-alkenes formed in such a system. 

Also, the copolymerisation of ethylene and a-olefins can be readily performed using Phillips catalysts. The copolymerisation of ethylene with 1-butene or 1-hexene is the basis of the large expanding linear low-density polyethylene market [28,37,43,237]. 

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