+ Site Statistics
References:
54,258,434
Abstracts:
29,560,870
PMIDs:
28,072,757
+ Search Articles
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ PDF Full Text
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Translate
+ Recently Requested

Radical polymerization of vinyl acetate with bis(tetramethylheptadionato)cobalt(II): coexistence of three different mechanisms



Radical polymerization of vinyl acetate with bis(tetramethylheptadionato)cobalt(II): coexistence of three different mechanisms



Chemistry 15(19): 4874-4885



The complex [Co(II)(tmhd)(2)] (4; tmhd = 2,2,6,6-tetramethylhepta-3,5-dionato) has been investigated as a mediator for controlled radical polymerization of vinyl acetate (VAc) and compared with the analogue [Co(II)(acac)(2)] (1; acac = acetylacetonato). A relatively well controlled process occurs, after an induction time, with 2,2'-azobis(4-methoxyl-2,4-dimethylvaleronitrile) (V-70) as radical initiator at 30 degrees C. However, whereas the polymerization essentially stops after about six initiator half-lives in the presence of 1, it continues with a first-order rate law in the presence of 4. The successful simulation of the kinetic data shows that 4 operates simultaneously by associative (degenerative transfer, DT) and dissociative (organometallic radical polymerization, OMRP) mechanisms. The occurrence of OMRP was confirmed by an independent polymerization experiment starting from an isolated and purified [Co(tmhd)(2)](PVAc) macroinitiator. The polymer molecular weight evolves linearly with conversion in accordance with the expected values for one chain per Co atom when DT is the predominant mechanism and also during the pure OMRP process; however, observation of stagnating molecular weights at long reaction times with concomitant breakdown of the first-order rate law for monomer consumption indicates a competitive chain-transfer process catalyzed by an increasing amount of Co(II). In the presence of external donors L (water, pyridine, triethylamine) the DT pathway is blocked and the OMRP pathway is accelerated, and polymerization with complex 4 is then about five times slower than with complex 1. The reversal of relative effective OMRP rate constants k(eff) (4>1 in the absence of external donors, 4<1 in their presence) is rationalized through competitive steric effects on Co(III)-C and Co(II)-L bond strengths. These propositions are supported by (1)H NMR studies and by DFT calculations.

(PDF emailed within 0-6 h: $19.90)

Accession: 055345978

Download citation: RISBibTeXText

PMID: 19308980

DOI: 10.1002/chem.200802388


Related references

Supported cobalt mediated radical polymerization (SCMRP) of vinyl acetate and recycling of the cobalt complex. Chemical Communications 2006(40): 4180-4182, 2006

Mechanistic insights into the cobalt-mediated radical polymerization (CMRP) of vinyl acetate with cobalt(III) adducts as initiators. Chemistry 14(13): 4046-4059, 2008

Effective cobalt mediation of the radical polymerization of vinyl acetate in suspension. Angewandte Chemie 44(22): 3439-3442, 2005

Highly efficient cobalt-mediated radical polymerization of vinyl acetate. Angewandte Chemie 44(7): 1101-1104, 2005

Cobalt-Mediated Radical Polymerization of Vinyl Acetate and Acrylonitrile in Supercritical Carbon Dioxide. Macromolecular Rapid Communications 37(6): 539-544, 2016

Exchange of organic radicals with organo-cobalt complexes formed in the living radical polymerization of vinyl acetate. Journal of the American Chemical Society 130(40): 13373-13381, 2008

Electronic and steric ligand effects in the radical polymerization of vinyl acetate mediated by beta-ketoiminate complexes of cobalt(II). Chemistry, An Asian Journal 4(8): 1257-1265, 2009

Free radical polymerization with long chain branching: continuous polymerization of vinyl acetate in t-butanol. Chemical Engineering Science 32(2): 167-178, 1977

Continuous reactors in free radical polymerization with branchingII experimental results on vinyl acetate polymerization. Chemical Engineering Science 25(10): 1559-1569, 1970

Kinetic studies on the sulfate radical-initiated polymerization of vinyl acetate and 4-vinyl pyridine in the presence of silica nanoparticles. Langmuir 21(17): 8001-8009, 2005

Controlled radical polymerization of vinyl acetate mediated by a vanadium complex. Chemical Communications 46(12): 2127-2129, 2010

Cobalt-Mediated Radical Copolymerization of Chlorotrifluoroethylene and Vinyl Acetate. Polymers 11(1), 2019

Investigation of the radical polymerization of vinyl acetate and its telomerization with carbon tetrachloride at high pressures. Russian Chemical Bulletin 14(3): 418-423, 1965

Key role of intramolecular metal chelation and hydrogen bonding in the cobalt-mediated radical polymerization of N-vinyl amides. Chemistry 18(40): 12834-12844, 2012

Atom transfer radical polymerization and copolymerization of vinyl acetate catalyzed by copper halide/terpyridine. Aiche Journal 55(3): 737-746, 2009