Ethylene polymerization molecular weight distribution

The living nature of ethylene oxide polymerization was anticipated by Flory 3) who conceived its potential for preparation of polymers of uniform size. Unfortunately, this reaction was performed in those days in the presence of alcohols needed for solubilization of the initiators, and their presence led to proton-transfer that deprives this process of its living character. These shortcomings of oxirane polymerization were eliminated later when new soluble initiating systems were discovered. For example, a catalytic system developed by Inoue 4), allowed him to produce truly living poly-oxiranes of narrow molecular weight distribution and to prepare di- and tri-block polymers composed of uniform polyoxirane blocks (e.g. of polyethylene oxide and polypropylene oxide). 

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. 

S-Methacryloyloxy-ljl -biadamantane, MBA, (Scheme 4) was efficiently polymerized anionically using [ l,l-bis(4/-trimethylsilylphenyl)-3-methylpen-lyl]lithium as the initiator, prepared in situ by the reaction of s-BuLi with l,l-bis(4-trimethylsilylphenyl)ethylene [17]. The polymerization took place at - 50 °C in order to avoid the solubility problems of the monomer, observed at - 78 °C. Narrow molecular weight distribution block copolymers of rather low molecular weights of PMBA with fBuMA and (2,2-dimethyl-... 

The molecular weight distribution of a polymer produced with a chain shuttling catalyst/CSA system is highly dependent on reaction conditions. The extent of reversibility with the catalyst/CSA pairs was therefore further explored through a series of polymerizations over a range of monomer conversions (i.e., yield). A representative example from this secondary screening process is described below for precatalyst 17. Several members from this well-studied bis(phenoxyimine)-based catalyst family [39] were identified as poor incorporators in the primary screen. A series of ethylene/octene copolymerizations using 17 was performed across a... 

Borstar A catalytic process for polymerizing ethylene. Use of two reactors, a loop reactor and a gas-phase reactor, allows better control of molecular weight distribution. The loop reactor operates under super-critical conditions to avoid bubble formation. Either Ziegler-Natta or metallocene catalysts can be used. The first commercial unit was installed in Porvoo, Finland, in 1995. 

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... 

Covalently attaching molecular catalysts to supports is a method that can minimize catalyst leaching. In 1998, a PS-supported titanocene was prepared by Barrett and de Miguel, which displayed 41 g-PE mmol-Ti h of activity. Soga and co-workers reported a series of poly(siloxane)-supported metallocene catalysts. These supported catalysts combined with MAO were found to have high activity for the (co)polymerization of ethylene, propylene, and ethylene/l-octene, though the reaction products typically displayed broad molecular weight distributions. ... 

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