Polymerization reactions with organic electron donors (OED) as initiators are presented herein. The metal‐free polymerization of various activated alkene and cyclic ester monomers was performed in short reaction times, under mild conditions, with small amounts of organic reducing agents, and without the need for co‐initiators or activation by photochemical, electrochemical, or other methods. Hence, OED initiators enabled the development of an efficient, rapid, room‐temperature process that meets the technical standards expected for industrial processes, such as energy savings, cost‐effectiveness and safety. Mechanistic investigations support an electron‐transfer initiation pathway that leads to the reduction of the monomer. 相似文献
Four acetyl cobalt complexes, [AcCo(CO)3P(p‐tolyl)3] ( 1 ; p‐tolyl=4‐Me‐C6H4), [AcCo(CO)3P(OPh)3] ( 2 ), [AcCo(CO)3P(NMe2)3] ( 3 ), and [AcCo(CO)2(dppp)] ( 4 ; dppp=1,3‐bis(diphenylphosphanyl)propane), were synthesized, characterized, and examined as catalysts for the unprecedented carbonylative polymerization of oxetanes. Copolymers containing ester (4‐hydroxyalkanoate) and/or ether units were obtained with complexes 1 and 2 , but not with complexes 3 and 4 either in the presence or absence of additional phosphorus ligands. The ester unit/ether unit ratio varied in the range 21:79–63:37, and the highest ester/ether ratio of 63:37 was achieved by using complex 1 in the presence of a further 5 equivalents of P(OPh)3. Although direct carbonylative polymerization is possible, preformation and ring opening of the γ‐lactone is also suggested as an alternative pathway. 相似文献
Organomanganate reagents [R3Mn]–Li+ (R = Bu, Me) were found to polymerize methyl methacrylate in the presence of potassium tert‐butylate. A conversion of the tacticity of the resulting poly(methyl methacrylate)s from heterotactic (mr = 54%) to isotactic (mm = 58%) was observed upon changing the R group of the initiator from Bu to Me. The addition of triisobutylaluminium was found to efficiently control M̄w and M̄w/M̄n of the resulting polymers. 相似文献
Novel Ni(Ⅱ)-based acetyliminopyridine complexes 1b, 2b, 3b (1-3b), which are synthesized from ligands 1a, 2a, 3a (1-3a) and [NiCl2(DME)], are suitable precursors for the catalysts that are necessary for ethylene oligomerization and polymerization reactions, activated by methylaluminoxane (MAO).The MAO-treated 1-3b presents an active catalytic center, which may oligomerize and polymerize ethylene to produce linear α-olefins and polyethylene, respectively. The molecular weight distributions of oligomers that are obtained are in good agreement with the Schulz-Flory rules for oligomers＞C4. The activity of oligomers show significant reliance on the structures of catalyst precursors. 相似文献
Summary: Procedures are developed to estimate kinetic rate coefficients from available rate data for the free radical solution polymerization of butyl acrylate at 50 °C. The analysis is based upon a complete mechanistic set that includes the formation of mid‐chain radicals through backbiting and their subsequent reaction, and contains no assumptions on how the rate coefficient for cross‐termination of mid‐chain and end‐chain radicals is related to the two homo‐termination rate coefficients. After a thorough statistical analysis, the results of the fitting are combined with other recent literature data to provide a complete set of individual rate coefficients for the butyl acrylate system. Monomer addition to a mid‐chain radical is estimated to be slower than addition to a chain‐end radical by a factor of more than 400. The termination of two mid‐chain radicals is estimated to be two orders of magnitude slower than termination of two end‐chain radicals, with the cross‐termination rate coefficient close to the geometric mean.
Formation of a mid‐chain radical by intramolecular chain transfer to polymer by a chain‐end radical. 相似文献
The thermal bulk polymerization of styrene is critically reviewed. There is still no generally accepted kinetic model for the thermal radical formation process, but ideal second‐ or third‐order models are widely used for modeling bulk systems. Since initiation and chain transfer reactions cannot be treated independently from one another as long as the same species is considered to be involved, it is concluded that non‐ideal kinetics, possibly in form of a (micro‐)viscosity dependency of the Mayo mechanism, are likely to be present. A mathematical model is presented that keeps the predictive capabilities of the Hui‐Hamielec model, but allows facile implementation of reaction specific modifications. Part 2 of this paper will focus on the effect of compartmentalization on the thermal polymerization of styrene.
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