Alexei A. Gridnev

Living polymerization: Rationale for uniform terminology

Polymer chemistry textbooks (e.g., B. Vollmert, Polymer Chemistry, Springer-Verlag: New York, 1973, p 37; G. Odian, Principles of Polymerization, 3rd ed., Wiley: New York, 1991, p 8; H. G. Elias, An Introduction to Polymer Science, VCH: Weinheim, 1997, p 51) classify polymerization reactions as chain, step, and living according to the dependence of their degree of polymerization ( ) or molecular weight ((M) over bar) on conversion. This article discusses the rationale for uniform terminology in living polymerization

The 25th anniversary of catalytic chain transfer

The transfer of hydrogen from a free radical to an olefin is catalyzed by some cobalt chelates. This reaction, when used in free-radical polymerization, can be called catalytic chain transfer (CCT) to a monomer. It allows the manufacture of oligomers that have defined molecular weights and are useful for a variety of applications. Because all the oligomers are getting terminal double bonds, they can behave as macromers. These macromers give rise to the formation of diblock and graft copolymers, telechelic polymers that have the same or different functional groups depending on the conditions and origins of the comonomers. The catalyst structure–property relation is discussed. Redox properties affect the CCT and provide additional leverage in controlling polymerization processes.

Synthesis of telechelic polymers initiated with selected functional groups by catalytic chain transfer

Catalytic chain transfer is found to be useful for making telechelic oligomers with a variety of initiating groups in a one-step reaction procedure. Two olefinic components are required, the first being a normal free-radical-polymerizable monomer such as a methacrylate. The second is a vicinal or other olefin generally considered to be unreactive in free radical polymerizations. Under conditions of radical polymerization in the presence of a CCT catalyst, the copolymer that results incorporates predominantly one molecule of the second component at the initiation of each polymer chain. The terminal end group is a geminal double bond. This geminal-disubstituted end group is radically polymerizable and would allow the preparation of functionalized arms on graft polymers.

Characterization of a series of phenyl‐capped vinyl‐terminated oligomers of styrene

Low molecular weight (MW) polystyrenes were synthesized by radical polymerization in the presence of catalytic chain-transfer agents. Synthetic conditions are controlled to produce molecules containing one methyl group at one end as well as a double bond at the other end, capped with a phenyl group. Individual oligomers were separated by liquid chromatography, and the properties were analyzed using NMR, ultraviolet–visible (UV–vis) spectroscopy, and size exclusion chromatography with light scattering. The UV–vis spectra, proton NMR spectra, and differential refractive-index increments exhibit an MW dependence of up to six–eight monomer units. The obtained dependencies can be used for precise characterization of the molecular weight distribution of polystyrene obtained by catalytic chain transfer. The double-bonded end groups were found to be exclusively in the transconfiguration for all oligomers.

Formation of organocobalt porphyrin complexes by reactions of cobalt(II) porphyrins with azoisobutyronitrile and organic substrates

Reaction of a cobalt(II) porphyrin with azoisobutyronitrile (AIBN) at 333 K provides a convenient source of a transient cobalt hydride that reacts with alkenes and alkynes to form secondary alkyl and vinyl complexes, respectively or alternatively with organic halides and epoxides in the presence of donor molecules to form primary alkyl and β-hydroxyalkyl complexes.