Initiating Species (initiating + species)

Distribution by Scientific Domains


Selected Abstracts


Simple Ruthenium Precatalyst for the Synthesis of Stilbene Derivatives and Ring-Closing Metathesis in the Presence of Styrene Initiators

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2007
Cheikh Lo
Abstract The ruthenium complex RuCl2(p -cymene)(IMes) was found to be an efficient precatalyst, with styrene as an initiating species, for the alkene metathesis of various styrenes into symmetrical and unsymmetrical stilbene derivatives and for the ring-closing metathesis reaction of a sterically hindered olefin leading to a tetrasubstituted cycloolefin. [source]


Fast living cationic polymerization accelerated by SnCl4.

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2005

A conventional catalyst, SnCl4, for cationic polymerization, combined with EtAlCl2 and an ester as an added base, has been used to realize the fast living cationic polymerization of not only alkyl vinyl ethers but also those containing hetero atoms in the pendant. Two important features of this system are the clearly defined roles of two Lewis acids: EtAlCl2 generates initiating species quantitatively from 1-(isobutoxy)ethyl acetate [CH3CH(OiBu)OCOCH3], and SnCl4 accelerates the polymerization, which proceeds with livingness (weight-average molecular weight/number-average molecular weight = 1.02,1.08) at a rate 103,105 greater than that with only EtAlCl2 (or Et1.5AlCl1.5). SnCl4 alone induces rapid and living-like polymerization but produces byproducts under similar reaction conditions. [source]


Stannous(II) trifluoromethane sulfonate: a versatile catalyst for the controlled ring-opening polymerization of lactides: Formation of stereoregular surfaces from polylactide "brushes"

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2001
Michael Möller
Abstract A general method for the controlled synthesis of polylactide in solution and from solid supports is presented. The evaluation of stannous(II) trifluoromethane sulfonate [Sn(OTf)2] and scandium(III) trifluoromethane sulfonate [Sc(OTf)3] as catalysts for the ring-opening polymerization (ROP) of L -, D -, and L,D -lactide is described as a route to polylactide using mild and highly selective conditions. These triflate catalysts must be used in conjunction with a nucleophilic compound such as an alcohol that is the actual initiating species via the active metal alkoxide species. Consistent with this process, 1H NMR analysis revealed that the ,-chain-end bears the ester from the initiating alcohol, and upon hydrolysis of the active metal alkoxide chain end, a ,-hydroxyl chain end was clearly detected. Polymers of predictable molecular weights and narrow polydispersities were obtained in high yields in accordance with a controlled polymerization process. The addition of base either as a solvent or additive significantly enhanced the polymerization rate with minimal loss to the polymerization control. The ROP of lactide isomers from an initiator, HO(CH2CH2O)3(CH2)11SH, self-assembled onto a gold surface using Sn(OTf)2 produced polylactide brushes under living conditions and provides the opportunity to prepare stereoregular or chiral surfaces by polymerization of enantiomerically pure monomers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3529,3538, 2001 [source]


"Charge transfer" polymerization,and the absence thereof!

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2001
H. K. Hall
Abstract Mechanisms for "charge-transfer" spontaneous polymerizations and cycloadditions between electron-rich olefins and electron-poor olefins were reviewed. As for propagation, literature proposals involving charge-transfer complexes were rejected. Instead, alternating copolymerization is ascribed to polar effects in free-radical reactions. As for spontaneous initiation, literature proposals involving charge-transfer complexes, with or without proton transfer, were rejected. Instead, the initiating species is postulated to be a tetramethylene zwitterion biradical, which may initiate either ionic homopolymerization or free-radical copolymerization. A new hypothesis proposes that any interaction that brings vinyl monomers close together may facilitate tetramethylene formation and spontaneous polymerization. These interactions include Coulombic, acid,base, hydrophobic,hydrophilic and templating,tethering interactions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2069,2077, 2001 [source]


Is the Addition-Fragmentation Step of the RAFT Polymerisation Process Chain Length Dependent?,

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006
Ekaterina I. Izgorodina
Abstract Summary: The chain length dependence of the addition-fragmentation equilibrium constant (K) for cumyl dithiobenzoate (CDB) mediated polymerisation of styrene has been studied via high level ab initio molecular orbital calculations. The results indicate that chain length and penultimate unit effects are extremely important during the early stages of the polymerisation process. In the case of the attacking radical (i.e., R, in: R,,+,SC(Z)SR,,,,RSC,(Z)SR,), the equilibrium constant varies by over three orders of magnitude on extending R, from the styryl unimer to the trimer species and actually increases with chain length, further confirming that K is high in this system. When the reactions of the cumyl leaving group and cyanoisopropyl initiating species, which are also present in CDB-mediated polymerisation of styrene in the presence of the initiator 2,2,-azoisobutyronitrile, are also included, the variation in K extends over five orders of magnitude. Although less significant, the influence of the R, group should also be taken into account in a complete kinetic model of the RAFT process. However, for most practical purposes, its chain length effects beyond the unimer stage may be ignored. These results indicate that current simplified models of the RAFT process, which typically ignore all chain length effects in the R and R, positions, and all substituent effects in the R, position, may be inadequate, particularly in modelling the initial stages of the process. [source]