ISSN:
1022-1352
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The polymerization of vinyl acetate (VA), methyl methacrylate (MMA), and methyl acrylate (MA) in ethyl acetate and tetrahydrofuran solution was initiated by the two-component initiating systems Fe(III) 2-ethylhexanoate or Co(II) acetylacetonate and pentamethyldisiloxane as co-initiator. Whereas Fe(III) 2-ethylhexanoate initiated the polymerization of all three monomers also in the absence of the siloxane, with an activity increasing from VA to MA, Co(II) acetylacetonate was completely inactive under these conditions. Addition of the siloxane co-initiator raised the monomer conversions with both transition metal initiators, particularly pronounced for MMA and MA. Number-average degrees of polymerization for poly(vinyl acetate) and poly(methyl acrylate) amounted to some hundred or less, but increased to several thousand for poly(methyl methacrylate). Electron spin resonance (ESR) spin trap experiments with N-tert-butyl-α-phenylnitrone (PBN) revealed that the transition metal compounds and the siloxane undergo a reaction in which free radicals are produced by oxidative cleavage of the co-initiator to generate hydrogen atoms which initiate the polymerization. With Fe(III) 2-ethylhexanoate PBN adducts of carbon-centered radicals are observed in the absence and in the presence of the monomers. By way of contrast, with Co(II) acetylacetonate only the hydrogen atom adduct to PBN is observed in the absence of the monomers. Co(acac)2 is likely to form a new complex with the co-initiator and the spin-trap molecules. The co-ordinated PBN competes with the two parent ligands of the complex for the liberated hydrogen atoms, however, due to favorable reaction rate the PBN-H adduct is formed preferably. The PBN adducts of carbon-centered radicals replace the PBN-H adduct when the monomers are added to the initiator solution, i.e. the H atoms are now preferably trapped by the monomer molecules.
Additional Material:
14 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1996.021970314
Permalink