Ethylene, alternating copolymerization

There exist many alternating copolymerizations ethylene or propene with alkyl acrylates [244], vinyl acetate with maleic anhydride [245], styrene with acrylonitrile [246], styrene with fumaronitrile [247], vinyl carbazol with fumaronitrile, vinyl ferrocenne with diethylfumarate [248], and further pairs or systems of three monomers [238, 249-253]. External conditions can support or hinder alternation. At not too high temperatures, vinyl acetate forms a donor—acceptor complex with maleic anhydride. Under these conditions (and in the presence of a radical initiator), an alternating copolymer is formed. The concentration of the complex decreases with increasing temperature above 363 K the complex cannot exist. Under these conditions, copolymerization yields a statistical copolymer whose composition depends on the composition of the monomer mixture [245]. 

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 same catalyst system, consisting of dineopentoxyvanadium oxychloride and triisobutylaluminum, is also suitable for the alternating copolymerization of isoprene with ethylene (20). 

When a sulfonated diphosphine is used as the ligand, the complex formed with palladium(0) catalyzes the alternating copolymerization of ethylene and... 

The alternating copolymerization of CO with ethylene proceeds via the reaction steps... 

Discussion Point DP7i While ethylene and norbornene give essentially alternating, amorphous copolymers, attempts to copolymerize ethylene and cyclohexene give only crystalline polyethylene. Which factors might contribute to these observations Unsaturated norbornenyl chain ends cannot arise by ji-H transfer... 

The alternating copolymerization of CO and ethylene has been studied in much detail over the past two decades. Although a number of Ni-based systems are known to catalyze this reaction,comparative studies have shown that Pd-based systems are by far the most active catalysts for this reaction. The lower activity of the Ni-based systems is somewhat surprising because the requisite CO and ethylene insertion steps are expected to be energetically more facile for the Ni-based systems. A recent study has shown that the energy barrier for CO insertion into the Ni-Me bond is less than 10 kcal mol" (Scheme 25), significantly lower... 

Studies of ethylene-vinyl aromatic monomer polymerizations continue to be published. Chung and Lu reported the synthesis of copolymers of ethylene and P-methylstyrene [28] and the same group extended these studies to produce and characterize elastomeric terpolymers which further include propylene and 1-octene as the additional monomers [29,30]. Returning to the subject of alternative molecular architectures for copolymers, Hou et al. [31] has reported the ability of samarium (II) complexes to copolymerize ethylene and styrene into block copolymers. 

The first palladium complex-catalyzed alternating copolymerization of ethylene and carbon monoxide was disclosed by Gough at ICI [8] in 1967. The polymer was produced at relatively low rates in severe reaction conditions (250 °C, 200 MPa). 

Rhodium carbonyls have also been reported as catalysts for the alternating copolymerization of ethylene and carbon monoxide [11], but activities and yields as well as molecular weights were again very low. 

Since the aforementioned investigations, significant advances in aqueous catalytic insertion polymerization have only been made over the past decade. Alternating copolymerization of olefins with carbon monoxide, polymerization of ethylene and 1-olefins, and polymerizations of norbomenes and of butadiene have been studied. 

A composition curve of the copolymerization is shown in Figure 7. The composition of one component in copolymers is exactly 50 mole % over a wide range of monomer concentration of the component in monomer mixtures. These results strongly indicate that an alternating copolymerization takes place in the ethylene-hexafluoroacetone system. 

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],... 

Waymouth has recently reported the alternated copolymerization of ethylene and propylene using 39. Preliminary analysis of the polymers using C NMR spectroscopy revealed that the alternated polymers are isotactic. ... 

Single-site catalysts offer many new opportunities for copolymerizing ethylene and styrene (Scheme 35). The alternating isospecific polymerization of these... 

Subjects specifically excluded are cycloolefin polymerizations catalyzed by naked nickel catalysts, palladium-catalyzed ethylene/carbon monoxide alternating copolymerizations, metathesis polymerizations of cyclic olefins, and diene polymerizations... 

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]. 

Carbonylation of some alkenes catalyzed by a cationic Pd complex yields polyketones, which are alternating copolymers. The polyketone 19 of ethylene or propylene named carilon is produced commercially by Shell [10]. A Chain-transfer mechanism for the alternating copolymerization of CO and ethylene was proposed... 

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