Ethene/a-olefin copolymerization

Table 5. Copolymerization parameters for ethene/a-olefin copolymerization by using different metallocene/MAO catalysts...

Processes of ethene/a-olefin copolymerization are of great practical importance. Copolymerization of ethene with small amounts of highest a-olefins (1-butene, 1 -hexene, 1 -octene) allows one to produce linear low density polyethylene (LLDPE), which is one of the most widely used large-scale polyolefin products. Polypropylene, modified with small amounts of ethene, exhibits higher impact strength compared to isotactic homopolypropylene. Copolymerization of propene with large amounts of ethene and terpolymerization of ethene/propene/diene result in amorphous elastomer materials (rubbers) [103]. 

For understanding the nature of the comonomer effect, it is also very important that the rate enhancement takes place in the sequential processes of homo- and copolymerization, i.e., when the ethene homopolymerization is carried out after the a-olefin homopolymerization or ethene/a-olefin copolymerization [122, 123] (Table 6). 

Table 3 Comonomer effect in ethene/a-olefin copolymerization using heterogeneous and supported ZN catalyst systems...

CEF - comonomer effect, Rcop - rate of ethene insertion in ethene/a-olefin copolymerization Rpol -rate of ethene homopolymerization... 

Water-soluble l,3-bis(di(hydroxyalkyl)phosphino)propane derivatives were thoroughly studied as components of Pd-catalysts for CO/ethene (or other a-olefins) copolymerization and for the terpolymerization of CO and ethene with various a-olefins in aqueous solution (Scheme 7.17) [59], The ligands with long hydroxyalkyl chains consistently gave catalysts with higher activity than sulfonated DPPP and this was even more expressed in copolymerization of CO with a-olefins other than ethene (e.g. propene or 1-hexene). Addition of anionic surfactants, such as dodecyl sulfate (potassium salt) resulted in about doubling the productivity of the CO/ethene copolymerization in a water/methanol (30/2) solvent (1.7 kg vs. 0.9 kg copolymer (g Pd)" h" under conditions of [59]) probably due to the concentration of the cationic Pd-catalyst at the interphase region or around the micelles which solubilize the reactants and products. Unfortunately under such conditions stable emulsions are formed which prevent the re-use... 

LCB-PE (long chain branched polyethylene) is not accessible through simple ethyl-ene/a-olefin copolymerization. Therefore, a bifunctional bimetallic catalyst was developed, in which one active center oligomerizes ethene to long-chain a-olefins, while the other copolymerizes them with ethene. 

One of the features of olefin copolymerization kinetics is the effect of comonomer on the rate of ethene or propene polymerization during ethene/a-olefin or propene/ a-olefin copolymerization, i.e., the so-called comonomer effect (CEF). The rate enhancement of ethene or propene polymerization in the presence of a comonomer is observed for conventional ZN catalysts [80, 113-123] and for homogeneous [124-133] and supported metallocenes [134—136] and post-metallocenes catalysts [137-140]. The increase in activity was remarked in the presence of such comonomers as propene, 2-methylpropene, 1-butene, 3-methylbutene,4-methylpentene-l, 1-hexene, l-octene,l-decene, cyclopentene, styrene, and dienes. 

Zhang W, Wei J, Sita LR. Living coordinative chain-transfer polymerization and copolymerization of ethene, a-olefins, and a,co-nonconjugated dienes using dialkylzinc as surrogate chain-growth sites. Macromolecules 2008 41 7829-7833. 

The class of monocyclopentadienylamido (CpA) titanium complexes has attracted the interest for the polymerization of a-olefins with bulky side groups. This arises since conventional Ziegler-Natta catalysts are less effective in starting the copolymerization of ethene with 4-methyl-l-pentene. Homogeneous catalysts of the zirconium cyclopentadienyl type (Cp2M) with methylaluminoxane exhibit a low catalytic activity. 

The copolymerization parameter rt which indicates how much faster an ethene is incorporated in the growing polymer chain than an a-olefin, when the last inserted monomer was an ethene unit, lies between 1 and 60 depending on the kind of comonomer and catalyst. The copolymerization parameter r2 is the analogous ratio for the a-olefin. The product r r2 is important for the distribution of the comonomer and is close to unity when using C2 symmetric metallocenes, indicating a randomly distributed comonomer. It is less than unity with a more alternating structure for Cs-symmetric catalysts [62-65] (Table 5). 

Half-sandwich metallocenes (120) (see Half-sandwich Complexes) play important role in the copolymerization of ethene and various a-olefins. They are distinguished by a sterically accessible active site. These catalysts are remarkably stable up to polymerization temperatures of 160 °C. 

Besides ethene, a variety of a-olefins can be effectively copolymerized with CO. These include... 

The practically most important copolymer is made from ethene and propene. Titanium- and vanadium-based catalysts have been used to synthesize copolymers that have a prevailingly random, block, or alternating structure. Only with Ziegler or single site catalyst, longer-chain a-olefins can be used as comonomer (e.g., propene, 1-butene, 1-hexene, 1-octene). In contrast to this, by radical high-pressure polymerization it is also possible to incorporate functional monomers (e.g., carbon monoxide, vinyl acetate). The polymerization could be carried out in solution, slurry, or gas phase. It is generally accepted [173] that the best way to compare monomer reactivities in a particular polymerization reaction is by comparison of their reactivity ratios in copolymerization reactions. 

Important for the copolymerization are the different ractivities of the olefins. The principal order of monomer reactivities is well known [187] ethene > propene > 1-butene > linear a-olefins > branched a-olefins. Normally propene reacts 5 to 100 times slower than ethene, and 1-butene 3 to 10 times slower than propene. Table 8 shows the reactivity ratios for the copolymerization of ethene with other olefins. The data imply that the reactivity of the polymerization center is not constant for a given transition metal compound but depends on the structure of the innermost monomer unit of the growing polymer chain and on the cocatalyst. 

With the aid of Ziegler catalysts it is possible to copolymerize isoprene with ethene and other a-olefins. Just like the analogous butadiene copolymers, the products are of alternating structure [518-521]. 

By the copolymerization of cyclic olefins such as cyclopentene or norbomene with ethene and other a-olefins, it is possible to obtain cycloolefin copolymers (COC) representing a new class of thermoplastic, amorphous materials [89, 103]. 

The objective of this paper is to demonstrate how this ri t way leads to the the estimation of the true copol]mierization parameters and how, as a consequence, new mechanistical details are obtained in ethene / higher o-olefin copolymerization reactions using our highly active MgH2 / TiCl / AlEt Ziegler-catalyst system. In previous publications whereby the homoplymerization of ethene was... 

When a-olefins such as propene and styrene are used in place of ethene or norbornene for this copolymerization, regio- and enantio-selectivities of the olefin insertion arise and the control of these becomes a difficult aspect for obtaining stereo-regular polyketones. In the head-to-tail copolymer, a chirotopic center exists per monomer unit. If the same enantioface of each a-olefin is selected by a catalyst, the resulting copolymer is isotactic in which all the chirotopic carbons in a polymer backbone possess the same absolute configuration. Thus, asymmetric copolymerization using a chiral catalyst is now attracting much attention. 

Heptaetiiyldec-9-enyl POSS monomer, 18, is a terminal a olefin monomer that has been employed by Tsuchida et al. to incorporate POSS moieties into polyolefins. Copolymers of tiiis monovinyl POSS monomer with ethene and propene (Fig. 12) were synthesi2ed vising different methyMumoxane-activated metallocene catalysts. POSS comonomer incorporation levels between 17 and 25 wt % were achieved, depending on wliich catalyst was used in the copolymerization. Incorporation of 25 wt % (1.2 mol %) of the vinyl-POSS 18 into the ethylene copolymer, 20, lowered the melting temperature by 18°C versus that of polyethene (PE). The thermal stability in air of vinyl-POSS 18/ethylene copolymer (0.7 mol % POSS) and 18/propylene copolymer... 

Hence, homo- and copolymerizations with propene or ethene and co-halo-a-olefins were also carried out on a zirconocene/MAO catalytic system. First copolymerization experiments of 11-chloroundec-l-ene with 1-hexene using a rac-Et(Ind)2ZrCl2/MAO catalyst system in methylene chloride and toluene show a complete deactivation with the former solvent because of fast side reactions however, in the case of... 

Recently, the application of phenoxy-imine-type vanadiirm (III) complexes 53-55 (Figure 23) for the copolymerization of ethene with polar hydroxyl group-functionalized a-olefins, such as Un-OH, 5-hexen-l-ol, and 3-butylene-l-ol, has been reported. The resulting polymers are random copolymers with a Un-OH incorporation of 13.9 mol%, molecular weights of up to 177000gmor and remarkable activities of up to... 

Due to the low polymerizability of carboxylic acids by metallocene catalysts, only a limited number of successful copolymerization reactions have been published. Beside copo-lymerization reactions of 10-undecenoic acid with ethene ° and propene,co- and terpolymerization reactions of norbomenecatboxylic add 34 (Figure 17) with a-olefins have been reported. " ... 

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