Ethylene polymerizations, highly active living

Yoshida et al. recently found that upon activation with MAO, bis(pyrrolide-imine)Ti complexes F13-5 could co-polymerize ethylene and NB in a highly controlled living manner at room temperature to yield co-polymers with very high molecular weights and narrow molecular weight distributions M >500000, PDI < They... 

The MAO-activated /3-enaminoketonato complexes of Figure 62 are moderately to highly active ethylene polymerization catalysts.1186 However, molecular masses are not very high (Mn < 100000). PEs produced with the first two systems, that is, R =GF3 and R2 = Ph or 2-theonyl, show rather narrow molecular mass distribution (Mw/ Mn < 1.35), indicative of quasi-living behavior. The post-polymerization experiments indicated that the catalyst lifetime is longer than 60 min even in the absence of ethylene. On the other hand, the third system, that is, R1 = CF3 and R2 = 2-furyl, produces PEs with rather broad polydispersities, although the only difference with the 2-theonyl-based catalyst is the replacement of an S atom with an O atom. 

A bewildering array of names are used to describe the various controlled/living radial polymerization techniques currently in use. These include stable free radical polymerization (SFRP) [35-38], nitroxide mediated polymerization (NMP) [39], atom transfer radical polymerization (ATRP) [40-42 ] and degenerate transfer processes (DT) which include radical addition-fragmentation transfer (RAFT) [43, 44] and catalyst chain transfer (CCT). These techniques have been used to polymerize many monomers, including styrene (both linear and star polymers) acrylates, dienes, acrylamides, methacrylates, and ethylene oxide. Research activity in this field is currently expanding at a very high rate, as is indicated by the many papers published and patents issued. 

Complex 6.21 represents a class of precatalysts that are active for both ethylene and propylene polymerization reactions. When Ar is phenyl, highly syndiotactic PP of low molecular weight is obtained. However, when Ar is pentafluro phenyl, highly syndiotactic living PP is the product. The same catalyst can also produce ethylene-propylene block copolymers. 

A porphinatoaluminum alkoxide is reported to be a superior initiator of c-caprolactone polymerization (44,45). A living polymer with a narrow molecular weight distribution (M /Mjj = 1.08) is ob-tmned under conditions of high conversion, in part because steric hindrance at the catalyst site reduces intra- and intermolecular transesterification. Treatment with alcohols does not quench the catalytic activity although methanol serves as a coinitiator in the presence of the aluminum species. The immortal nature of the system has been demonstrated by preparation of an AB block copolymer with ethylene oxide. The order of reactivity is e-lactone > p-lactone. 

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. 

The MAO-activated 138 and 137, effective in the living homopolymerization of ethylene and propylene, also promote their block co-polymerization. This approach broadens remarkably the utility of living catalysts because it allows the preparation of block co-polymers with high glass or melting transition blocks from common commercial monomers such as ethylene and propylene. These materials could have applications as compatibilizers and elastomers.1232,1233 Using complex 138, propylene has been first homopolymerized to sPP for 2h in toluene at 0°C (Mn = 38400 Mw/Mn = 1.11). Then, an ethylene overpressure was applied, and in 1 additional h an sPP-/W< (j -poly(E-r -P) diblock co-polymer was obtained (Mn = 145 100, A/w/A/ = 1.12). The microstructure of this diblock co-polymer is shown in Scheme 48. This co-polymer has a Tm of 131 °C while the ethylene-propylene block (E = 33 mol%) has a TR of —45 °C.1175 A detailed morphological and thermodynamic characterization of these co-polymers has been reported.1234... 

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