Copolymerization using palladium catalysts

J. Kiesewetter, B. Arikan, and W. Kaminsky, Copolymerization of eth-ene with norbomene using palladium(II) a-diimine catalysts Influence of feed composition, polymerization temperature, and ligand structure on copolymer properties and microstructure, Polymer, 47 (10) 3302-3314, May 2006. 

Palladium catalysts are used for the copolymerization of ethylene and methylacrylate (281). The copolymers contain both alkyl and ester side chains. 

Polymerization Reactions. The enantioselective co-polymerization of styrenes and carbon monoxide has been achieved by the use of a palladium catalyst based on the (5,5)-r-Bu-box ligand. Copolymerization of p-/er/-butylstyrene (TBS) and carbon monoxide in the presence of 0.1 mol % chiral catalyst afforded the alternating co-polymer with a highly isotactic microstructure and excellent optical purity (eq 22). The stereoregularity of the polymer is >98% and the polymer exhibits high molar rotation. ... 

For both dasses of four-membered chelate forming hgands (Scheme 8.6, 2 and 3), the phenyl-substituted systems do not show essentially catalytic activity in the copolymerization of ethene in the presence of propene using palladium acetate and Ihfif, -,) as the promoter and methylene chloride as the solvent. However, increasing the size of the R substituent leads to very efficient catalysts (turnover frequency up to 2x K/ mol (mol li) at 70°C). The incorporation of propene under the experimental conditions is more efficient for the mefhane-diphosphine 2 [40]. 

As a consequence of the living nature of the copolymerization wifh fhis catalyst, palladium-capped block copolymers of norbornene and ethene as well as of norbornene, ethene, and styrene were synthesized [61]. Higher activities (up to ten times higher) were observed for a series of oxazohne-phosphine complexes (e.g., 31). Several complexes, modified with bisphosphine monooxide and monosulfide ligands (Scheme 8.8, 32 and 33), were also used as catalysts precursors. The best reported turnover frequency is 0.6x10 mol (molh) at 80°C [62, 63]. A slightly lower activity was observed for fhe ketophosphine containing catalyst precursor 34 [64]. The activity of catalyst precursors 35, 36, and 37 is even lower [65]. 

In addition to propylene, other nonconjugated olefins have been copolymerized with CO using enantiopure palladium catalysts. Allylbenzene, 1-butene, 1-heptene, 4-methyl-l-pentene, and cis-2-butene [84,85] as well as hydroxy- and carboxylic acid-functionalized monomers [87] have been polymerized to give optically active polymers. Waymouth, Takaya and Nozaki have recently reported the enantioselective cyclocopolymerization of 1,5-hexadiene and CO [88,89]. 

In addition to propylene, other nonconjugated olefins have been copolymerized with CO using enantiopure palladium catalysts. Allylbenzenes,... 

N-heterocyclic carbene/palladium complexes were successfully used as catalysts in the copolymerization of bisphenol and carbon monoxide (Scheme 29)... 

Palladium catalysts also promote copolymerization of SO2 with alkenes analogously to copolymerization of CO and alkenes (Eq. 7.24) [119]. The catalyst activities for the polysulfone synthesis are lower by an order of magnitude than those for the polyketone synthesis. Perfectly alternating copolymers can be obtained by use of cationic methylpalladium(II) complexes, [PdMe(CH3CN)L2]BF4 (L2 = l,3-bis(diphenylphosphino)propane and 1,2-bis(2,5-dimethylphosphinolato)benzene), in contrast to a lower degree of alternation provided by a radical polymerization [120]. 

Up to now, palladium complexes do not play a significant role in the hydroformylation of olefins [1]. However, because of their widespread use in the related hydrocarboxylation, hydroesterification, and olefin copolymerization with CO [2], occasionally their utility for hydroformylation was elucidated [3]. Moreover, palladium catalysts have been used for the hydroformylation of aryl and enol triflates to produce the corresponding unsaturated aldehydes [4]. 

Kaminsky et al. succeeded in E-N copolymerizations by using a-diimine palladium catalysts [111, 112]. The Tg values of E-N copolymers produced are very high and range from 98 to 217°C [111, 112], Copolymers produced at norbomene molar fraction (xn) > 0.80, as well as homo-polynorbomenes, show no Tg values or values under 350°C, and decompose above 350°C. 

Gottfried, A.C. and Brookhart, M. (2003) Living and block copolymerization of ethylene and a-olefins using palladium (ll)-a-diimine catalysts. Macromolecules, 36,3085-3100. 

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