Copolymerization with olefins

However, the practical, direct synthesis of functionalized linear polyolefins via coordination copolymerization olefins with polar monomers (CH2 = CHX) remains a challenging and industrially important goal. In the mid-1990s Brookhart et al. [25, 27] reported that cationic (a-diimine)palladium complexes with weakly coordinating anions catalyze the copolymerization of ethylene with alkylacrylates to afford hyperbranched copolymers with the acrylate functions located almost exclusively at the chain ends, via a chain-walking mechanism that has been meticulously studied and elucidated by Brookhart and his collaborators at DuPont [25, 27], Indeed, this seminal work demonstrated for the first time that the insertion of acrylate monomers into certain late transition metal alkyl species is a surprisingly facile process. It spawned almost a decade of intense research by several groups to understand and advance this new science and to attempt to exploit it commercially [30-33, 61]. 

The literature on late-transition metal catalysts is very large and keeps growing as new complexes are developed. Several families have been well studied such as Brookhart (Ni and Pd see Figure 2.14(d)), Gibson-Brookhart (Co and Fe) and Grubbs (neutral Ni) catalysts. Some of their properties are very enticing these catalysts are much less sensitive to polar compoimds and can be used, although not in industrial-relevant conditions, to copolymerize olefins with polar monomers such as acrylates and methylacrylates [28]. 

In order to achieve higher-performing engineering thermoplastic properties, significant modification of the polymer backbone is required. The use of carbon monoxide as a comonomer has been of interest based on its abundance and its ability to confer functionahty. However, conventional early transition metal polyolefin catalysts are ineffective at copolymerizing olefins with carbon monoxide. 

The free-radical reaction may be equally initiated by photoactivated sulfur dioxide (3S02)442 (equation 79). On the other hand, polysulfones are obtained by radical copolymerization of appropriate olefins with sulfur dioxide443-449, and similarly, uptake of sulfur dioxide by a radical-pair formed by nitrogen extrusion from an azo compound yields the corresponding sulfone450 (equation 80). Correspondingly, alkylbenzenes, dibenzoyl peroxide, and sulfur dioxide yield sulfones under thermal conditions451... 

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... 

This type of reaction is involved as an intermediate step in few synthetically useful reactions, in the formation of polysulfones by copolymerization of an olefin with SO 2, as well as in aerosol formation in polluted atmospheres. We will discuss later in some detail the most important chain reactions involving step 11. However, Good and Thynne determined the Arrhenius parameters for the addition of methyl and ethyl radicals to SO2 in gas phase, the rate constants being 5 x 10 and 4 x 10 s respectively at ambient... 

Palladium(II) complexes possessing bidentate ligands are known to efficiently catalyze the copolymerization of olefins with carbon monoxide to form polyketones.594-596 Sulfur dioxide is an attractive monomer for catalytic copolymerizations with olefins since S02, like CO, is known to undergo facile insertion reactions into a variety of transition metal-alkyl bonds. Indeed, Drent has patented alternating copolymerization of ethylene with S02 using various palladium(II) complexes.597 In 1998, Sen and coworkers also reported that [(dppp)PdMe(NCMe)]BF4 was an effective catalyst for the copolymerization of S02 with ethylene, propylene, and cyclopentene.598 There is a report of the insertion reactions of S02 into PdII-methyl bonds and the attempted spectroscopic detection of the copolymerization of ethylene and S02.599... 

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. 

The diimine palladium compounds are less active than their nickel analogs, producing highly branched (e.g., 100 branches per 1,000 carbons) PE. However, they may be used for the copolymerization of Q-olefins with polar co-monomers such as methyl acrylate.318,319 Cationic derivatives, such as (121), have been reported to initiate the living polymerization of ethylene at 5°C and 100-400 psi.320 The catalyst is long-lived under these conditions and monodisperse PE (Mw/Mn= 1.05-1.08) may be prepared with a linear increase in Mn vs. time. 

However, despite nearly 50 years of intense activity and progress, there are no commercially viable catalysts for the polymerization of acrylates or the controlled copolymerization of simple olefins with polar functional monomers. The development of a catalytic system capable of such controlled copolymerization would constitute a quantum advance in the plastics industry. 

There have also been several papers [61-63] on the importance of carefully establishing the reaction mechanism when attempting the copolymerization of olefins with polar monomers since many transition metal complexes can spawn active free radical species, especially in the presence of traces of moisture. The minimum controls that need to be carried out are to run the copolymerization in the presence of various radical traps (but this is not always sufficient) to attempt to exclude free radical pathways, and secondly to apply solvent extraction techniques to the polymer formed to determine if it is truly a copolymer or a blend of different polymers and copolymers. Indeed, even in the Drent paper [48], buried in the supplementary material, is described how the true transition metal-catalyzed random copolymer had to be freed of acrylate homopolymer (free radical-derived) by solvent extraction prior to analysis. 

The cationic Pd(II) catalysts exhibit effective copolymerizations of ethylene and other a-olefins with polar-functionalized comonomers, with the majority of insertions occurring at the ends of branches. Among the best tolerated monomers are those bearing fluorine or oxygen-containing functionalities, such as esters, ketones, and ethers. The copolymerization of ethylene and acrylates, attractive because the monomers are inexpensive and the copolymers exhibit unique physical properties, has been well-studied mechanistically [27,69], Examples of copolymerizations of ethylene and a-olefins with methyl acrylate are shown in Table 4. In general, the amount of comonomer incorporation varies linearly with its reaction concentration and... 

Table 4 Copolymerizations of ethylene and a-olefins with methyl acrylate (MA) by Pd(II) a-diimine catalysts3...

The Diels-Alder adduct of 1,5-cyclooctadiene with hexachlorocyclo-pentadiene was homopolymerized or copolymerized (113) with cyclic olefins using tungsten halide salts with either organoaluminum or organo-tin cocatalyst to give thermally stable flame- and oil-resistant polymers. 

Generally speaking, a monomer with electron-releasing groups will be more rapidly polymerized by cationic initiators. Anionic initiators polymerize olefins with electron-withdrawing groups more rapidly. A more sensitive test of the nature of the reaction is the behavior of a mixture of two such monomers in copolymerization in which they compete for the intermediate. This will be discussed in more detail in Chapter XII on polar versus radical mechanisms. 

In summary, the prediction that (E)-(Z) selectivity in the ethene/intemal olefins copolymerization with group 4 metallocenes can be achieved by using ligands of suitable symmetry has been proved. In particular, it has been shown that C2- and Os-symmetric metallocenes are able to copolymerize ethene with (Z)- and ( >butene, respectively. 

There are two principal ways to synthesize functional fluoropolymers (a) polymerization of functional fluoromonomers or copolymerization of fluoro-olefins with functional monomers, and (b) modification of common... 

Ethylene, isobutylene, tert-butylethylene, and other olefins also copolymerize with thiocarbonyl fluoride. What is astonishing is that tetramethylethylene, which is so sterically hindered as to be unreactive in olefin polymerizations, copolymerizes readily with thiocarbonyl fluoride. Most of these comonomers do not behave in the same way as propylene. They give products with compositions more closely approximating the monomer mixture used. 

The opacity of a crystalline polymer may also be reduced by copolymerization. Even so, polymethylpentene (TPX) is transparent because the n values of the amorphous and the crystalline phase are quite similar. Transparency may also be enhanced by copolymerization of the methylpentene with a small amount of another polymerizable olefin with a similar n. 

Alternating Copolymerization of Olefins with CO catalysed by palladium complexes generated from the sulfonated ligands 29 (Table 2 x=3 m=0,l n=0) and 108 (Table 6) in aqueous media263 or from 20 (Table 2 n=0 R=H acid-form) and 21 (Table 2 R=Ph n=2,3 acid-form) in methanol.335... 

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 kinetic technique was extensively used by Dainton and his associates (3, 4) particularly in their studies of the copolymerization of olefins with sulfur dioxide to 1 1 polysulfones. To check their results, they compared the heats of polymerization calculated from the ceiling... 

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