Copolymerization of alkenes

PALLADIUM-CATALYZED ALTERNATING COPOLYMERIZATION OF ALKENES AND CARBON MONOXIDE... 

The synthesis and properties of heat-resistant polyazomethines containing 2,5-disubstituted oxadiazole fragments, being insulators convertible into semiconductors by doping with iodine, have been described. The radical copolymerization of alkenes with the fluorescent co-monomer 2-/-butyl-5-(4 -vinyl-4-biphenylyl)-l,3,4-oxadiazole has resulted in useful macromolecular scintillators. Anionic polymerization of 2-phenyl-l,3,4-oxadiazolin-5-one has produced a nylon-type product <1996CHEC-II(4)268>. 

Although the literature contains much on copolymerizations of cyclic monomers, including data on monomer reactivity ratios, the reader is cautioned that most of the data are less reliable than corresponding data for radical copolymerizations of alkenes (Chap. 6). The... 

Counterion effects similar to those in ionic chain copolymerizations of alkenes (Secs. 6-4a-2, 6-4b-2) are present. Thus, copolymerizations of cyclopentene and norbomene with rhenium- and ruthenium-based initiators yield copolymers very rich in norbomene, while a more reactive (less discriminating) tungsten-based initiator yields a copolymer with comparable amounts of the two comonomers [Ivin, 1987]. Monomer reactivity ratios are also sensitive to solvent and temperature. Polymer conformational effects on reactivity have been observed in NCA copolymerizations where the particular polymer chain conformation, which is usually solvent-dependent, results in different interactions with each monomer [Imanishi, 1984]. 

As stated above, the discovery of efficient catalysts for the copolymerization of alkenes originated from a study of the alkoxycarbonylation of ethylene in methanol (MeOH) to methyl propionate (eq. (1)). 

The alternating copolymerization of alkenes with CO is on its way to commercial-zation (cf Section 2.3.4) [244 a]. This reaction can also be performed in aqueous media the catalyst of choice is based on ligand-modified Pd [218 k, 245]. 

Early metal-metallocene-alkene polymerization catalysts permit the synthesis of highly isotactic polypropylene . They rely on controlling the stereochemistry of alkene insertion by the use of chiral C2 symmetric metallocenes . Late metal systems for alkene polymerization , and copolymerization of alkenes and CO , have also been developed. 

Smooth copolymerization of alkenes with dienes would produce polyolefins with cyclic groups or vinyl pendant groups. The copolymerization was studied by using early transition metal complexes, including metallocene, half metallocene, and nonmetallocene complexes of Zr. 

Copolymerization of alkenes with nonconjugated dienes is conducted by using zirconocene, CGC catalyst, and the catalyst composed of iron di-iminopyridine complexes (Eq. 25). The former two catalysts give the copolymer,... 

Pd complex-catalyzed copolymerization of alkene and CO affords the polyketones via alternating insertion of the two monomers [166, 167]. The polymer growth involves migratory insertion of CO into the metal-carbon bond as a crucial step, which is unique to the late transition metal complexes such as Ni, Pd, Rh, and Co. The copolymerization of allenes and methylenecydopropanes with CO has attracted much less attention than the alkene-CO copolymerization, although it would provide further functionalized polyketones due to the dual functionality of the dienes and the derivatives. 

The copolymerization of alkenes with carbon monoxide has attracted the attention of chemists for many years [1]. Following the commerciahzation of Carilon, an alternating olefin carbon monoxide terpolymer based on ethene and small amounts (5-10%) of propene (Scheme 8.1, 1), by Shell [2, 3] in the 1990s interest in the identification of new and more active catalysts and of the stereochemical characteristics of the reaction has grown. 

In a patent filed as early as 1948, Reppe and Magin described the reaction of ethylene with carbon monoxide in the presence of an aqueous solution of potassium nickel(II) cyanide at 150°C and 150 bar [4], Along with propionic acid and diethyl ketone, higher molecular weight solid polyketones were obtained. The alternating copolymerization of alkenes with carbon monoxide has received continued industrial and academic interest, one reason being the low cost of carbon monoxide as a monomer [5],... 

Palladium-catalyzed copolymerization of alkenes with carbon monoxide leading to polyke-tones46 48 represents another example of dicarborative addition. With terminal or other unsymmetrically substituted prostereogenic alkenes a polymer with stereogenic centers along the polymer backbone is generated. 

The rates of insertion of ethylene into Pd-alkyl and Pd-acyl bonds have been evaluated for this type of systems, in particular [Pd(R)(C2H4)(L-L)]+ (R = alkyl, acyl L-L = phen, 1,3-diphenylphosphinopropane) [117,118], Lower activation barriers for the acyl complexes were consistently found with AAG (alkyl-acyl) about 2 kcal for the phen complexes and 4 kcal for the phosphino derivatives. Insertion barriers for CO insertion into the Pd-alkyl bond are even lower, making the alternating copolymerization of alkenes and CO possible and almost flawless (a perfect sequence of CO insertion into M-alkyl and alkene insertion into M-acyl with absence of alkene insertion into M-alkyl) [119]. 

This reaction profile, also called carbonylation, governs the reactivity of Pd-carbonyl complexes. Anionic M[Pd(CO)l3], for instance, catalyzes the reductive carbonylation of esters.f On the other hand, Pd(CO)(PPh3)3 was reported to catalyze the carboxymethy-lation of organic halides and the cyclocarbonylation of cinnamyl halides.f " However, the Pd-CO complexes are most often generated in situ from preformed alkyl -palladium complexes and CO under stoichiometric or catalytic conditions, for example, in the copolymerization of alkenes and CO. Decarbonylation reactions also involve the intermediacy of Pd-CO complexes. In this case, migratory deinsertion (Sect, n.3.1), that is, the microscopic reversal of the migratory insertion, takes place. 

Also interesting is the preparation of cationic palladium complexes, such as [MePd (PMe3)2]Xt i and [(C6F5)Pd(CO)(PPh3)]X,t considering the fact that cationic palladium complexes are believed to be the actual catalytic species in several Pd-catalyzed processes, an example of which being the copolymerization of alkenes and... 

The insertion of ethylene and a-olefins into acyl groups is one step of the remarkably selective copolymerization of alkenes and CO to form an alternating copolymer. This process was developed at Shell Chemicals and is discussed in Chapter 17. As depicted in Scheme 9.10, the relative rates for insertion of an alkene into an alkyl group and an acyl group are one factor that controls the selectivity. For high selectivity, the insertion of ethylene into the acyl group must be faster than insertion of ethylene into an alkyl group. ... 

Free Radical Copolymerization of Alkenes with Unsaturated Heterocyclic Compounds... 

Drent, E. Budzelaar, P. H. M. PaUadium-catalyzed alternating copolymerization of alkenes and carbon monoxide. Chem. Rev. 1996, 96, 663-682. 

The living nature of acylpalladium and other organopalladium species permits a series of their interconversions under one set of conditions, one representative example being the Pd-catalyzed copolymerization of alkenes and CO (Sect. VL4.2). A series of such processes can also occur in cyclic manners, and they are the subject of this subsection. Some chemists call combinations of two same or different successive processes tandem processes. These chemists have tended to call successively occurring multiple processes cascade processes, which may include tandem processes. Other chemists, on the other hand, would call them domino processes. Since these are rather loosely defined terms involving fundamentally nonchemical words, selection among them is a subjective matter, and all are used here and throughout this Handbook. 

C.ii.b. Double and Multiple Acylpalladation Cascades. The alternating copolymerization of alkenes and discussed in Sect. VI.4.2 falls into this category. The scope of... 

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