Branched polyethylene imine

Fig. 4 Examples (a) PEGylated monolayer (b) Glucose-modified monolayer (c) Surface-attached hyper-branched polyethylene imine and (d) Surface-attached hyperbranched polyglycerols of surface-coatings that resist the nonspecific adsorption of proteins. (Figure reproduced in part with permission from [41])...

Cationic polymerization of unsubstituted aziridine leads to branched polyethylene imine). This is attributed to the reaction of protonated aziridine formed either directly (protonic acids as initiators) or through proton transfer from alkylated aziridine (alkylating agents as initiators), with NH groups along the chain [162,163] ... 

The structure-reactivity relationship for polyamine derivatives in activated ester hydrolysis was previously established [46]. Polyvinylamine (PVA), linear (LPEI) and branched (41% branching) polyethylene imine (BPEI) as well as their dodecyl- and imidazole-substituted derivatives with an approximate and equal degree of substitution (16-20%) were applied as catalysts. The compoundsp-NPA and 4-acetoxy-3-ni-trobenzoic acid (ANBA) as well as some of their homologues were used as substrates. At an excessive catalyst concentration relative to the substrate concentration, reactions proceeded at pseudo first order. In each series of polymers, the reaction rate constant was increased considerably by substitution of dodecyl (hydrophobic site) by imidazolyl (catalytic center) and when a charged substrate (electrostatic effect) was employed. At an equal degree of substitution, the catalytic activity increased in the following order LPEK PVA < BPEI. 

Branched and linear polyethylene imine), and poly(vinylimidazole), were similarly cross-linked in the presence of template Cu2+ or Co2+ ion, but no enhancement of selectivity towards the same metal ions was achieved 37>. 

There are two different ways of preparing the simplest polyamine, polyethylen-imine. The first method leads to a commercial polymer. The parent monomer (aziri-dine) is used and the resulting polymer is highly branched due to pronounced chain transfer. The second method, leading to linear polyethylenimine, requires the preparation of polyoxazoline intermediate and is discussed in the next section. 

Polyethylene imines, PEI, are strongly cationic and strongly branched polymers with a molar mass between 100,000 and 1,000,00 (g/mole)... 

Late transition metal catalysts that are highly active and produce high molecular weight polyolefins were recently reported [198,199]. For example, nickel and palladium-diimine catalysts 67 produce highly branched polyethylene that is totally different from those produced by conventional or homogeneous Ziegler-Natta catalysts [200]. On the other hand, iron and cobalt 2,6-pyridine bis(imine) complexes 68 give linear polyethylene [201,202]. These catalysts are used with co-catalysts such as MAO, and the active species are cationic. Neu-... 

Because of the relative rates of chain propagation versus chain walking, polymers from the bis(imine) catalysts can be quite different depending on the metal. Nickel complexes form polymers with mostly shorter-chain branches and more crystallinity while polyethylene from the palladium analogs is more highly branched, to the point it can be amorphous. The palladium complexes also have the abihty to incorporate remarkably high (1 10 mole percent) amounts of polar monomers such as methyl acrylate and methyl vinyl ketone, though at considerable loss in activity. ... 

Fig. 1). These include linear polyethylene and polypropylene imines of varying degree of polymerization (Pn = 10 to 20) in non-methylated (PEI and PPI) and methylated (PMEI and PMPI) forms, which were specifically synthesized. Hexaazadocosane, which may be regarded as a model for a PPI with Pn = 6, was prepared by Michael addition of acrylonitrile to spermidine [12]. In addition, a commercially available PEI with high molecular mass and with a branched polymer architecture was employed. 

Polyethylene, elastomeric (yery highly branched) Poly (ethylene imine)... 

The sheer size and value of the polyethylene industry ensure that there is continued research, progress, and development in catalysis, for their potential commercial impact. Although this whole subject is not within the scope of this chapter, we mention a couple of aspects of the progress, which offer the potential to impact this industry. In 1995, DuPont introduced work, carried out with them at the University of North Carolina—via the largest patent applicafion ever in the USA. They disclosed what are described as post-metallocene catalysts. These are transition and late transition metal complexes with di-imine ligands, which form part of the DuPont Versipol technology. Such catalysts create highly branched to exceptionally linear ethylene homopolymers and linear alpha-olefins. Late transition metals offer not only the potential for the incorporation of polar comonomers, which until now has only been possible in LDPE reactors, but also their controlled sequence distribution, compared to the random composition of free radical LDPE copolymers. Such copolymers account for over 1 million tons per annum [20]. Versipol has so far only been cross-licensed and used commercially by DuPont Dow Elastomers (a former joint venture, now dissolved) in an EPDM plant. 

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