| Synthesis of Well Defined Polymers by Controlled Radical Polymerizations |
30 JUN 95 |
19 pages |
| Authors:
Krzysztof Matyjaszewski; Scott Gaynor; Dorota Greszta; Daniela Mardare; Takeo Shigemoto; CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF CHEMISTRY
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 | Controlled radical polymerizations can be achieved by using either unimolecular or bimolecular exchange between growing radicals and dormant chains. Dormant chains can be represented as either covalent species or organometallic compounds. Systems based on alkoxyamines, organochromium, organoaluminum compounds, and alkyl iodides are discussed in detail. In many systems, straight semilogarithmic plots indicate a constant number of growing radicals. A linear increase of molecular weights with conversion indicates a constant number ... |
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| Radical Polymerization of Vinyl Acetate and Methyl Methacrylate Using Organochromium Initiators Complexed with Macrocyclic Polyamines |
30 JUN 94 |
3 pages |
| Authors:
Daniela Mardare; Scott Gaynor; Krzysztof Matyjaszewski; CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF CHEMISTRY
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| Poly(vinyl)acetate and poly(methyl methacrylate) with controlled molecular weights and narrow polydispersities (1.55-1.68) were prepared by radical polymerization using initiators based on redox systems: benzoyl peroxide and Cr(OAC)2 complexed by macrocyclic polyamines, in THF, at ambient temperatures. Structure of N-based ligands affects the initiation rate and propagation control. The highest degree of control was achieved by using chromium atom complexed by 1,4,7,10,13,16-hexaazacyclooctadecane trisulfate. |
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| Radical Polymerization of Vinyl Acetate in the Presence of Trialkyl Phosphites |
30 JUN 94 |
3 pages |
| Authors:
Krzysztof Matyjaszewski; Dorota Greszta; Daniela Mardare; CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF CHEMISTRY
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| Radical polymerization of vinyl acetate initiated by BPO in the presence of different phosphites was studied. As it was observed, trialkylphosphites enhance polymerization rates. The molecular weights of polymers are affected by the initiator concentration and can be adjusted to higher or lower values. Polydispersities do not change with conversion and are lower than for PVAc obtained with BPO as an initiator (usually M sub w /M sub n = ... |
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| Synthesis of Well Defined Polymers by Radical Polymerization |
30 JUN 94 |
3 pages |
| Authors:
Scott Gaynor; Dorota Greszta; Takeo Shigemoto; Daniela Mardare; Krzysztof Matyjaszewski; CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF CHEMISTRY
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| Several approaches to synthesis of polymers with controlled molecular weights, desired end groups and low polydispersities, by controlled radical polymerization are discussed. The first one is based on nitroxyl radicals such as TEMPO which can react reversibly with propagating radicals. The position of the equilibrium constant depends on the nature of the radical, solvent and temperature. Polymerization rates in systems involving polar monomers (methyl methacrylate, methyl acrylate, vinyl acetate) are ... |
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| Thermal Polymerization of Styrene in the Presence of Stable Radicals and Inhibitors |
30 JUN 94 |
4 pages |
| Authors:
Daniela Mardare; Krzysztof Matyjaszewski; CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF CHEMISTRY
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| Thermal polymerization of styrene in the presence of several radical scavengers and inhibitors was investigated. Rates, molecular weights and polydispersities depend on the nature of the scavenger, on its concentration and reaction temperature. In the best controlled systems, molecular weights up to M sub n approx. 10,000 and polydispersities M sub w/M sub n approx. 1.2 were observed. It is proposed that in addition to the reversible activation by the ... |
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| New Initiators for Controlled Radical Polymerization of Acrylic Monomers |
30 JUN 94 |
4 pages |
| Authors:
Daniela Mardare; Krzysztof Matyjaszewski; CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF CHEMISTRY
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| Polymerization of acrylic monomers was redox initiated by mixtures (1:1) of transition metal derivatives (acetates, metallocenes) with arenediazonium salts. In most cases, molecular weights increase with the conversion and polydispersities are lower than in a typical radical or anionic polymerization at these temperatures. Trapping experiments and relative monomer reactivities based on copolymerization studies indicate that these polymerizations proceed via a radical mechanism. The improved polymerization control can be ascribed to ... |
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| Control of Molecular Weights and Polydispersities in Radical Polymerization of Styrene in the Presence of Stable Radicals |
30 JUN 94 |
5 pages |
| Authors:
Daniela Mardare; Krzysztof Matyjaszewski; Takeo Shigemoto; CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF CHEMISTRY
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| Radical polymerization of styrene was investigated by initiation with benzoyl peroxide and AIBN, in the presence of nitroxy-based stable radical scavengers. The effects of the concentration of the nature and concentration of nitroxy radicals and the nature and concentration of the radical initiators on the kinetics, evolution of molecular weights and polydispersities of polystyrenes prepared at various temperatures are also discussed. |
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| 'Living' Radical Polymerization. 1. Possibilities and Limitations |
30 JUN 94 |
27 pages |
| Authors:
Krzysztof Matyjaszewski; Dorota Greszta; Daniela Mardare; CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF CHEMISTRY
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| Possibility of the synthesis of well-defined polymers by radical polymerization is discussed. Kinetic analysis demonstrates that the preparation of polymers with controlled macromolecular structure in a 'living' radical process requires low stationary concentration of growing radicals which are in a dynamic equilibrium with dormant species. Three approaches are described. First, when growing radicals react reversibly with scavenging radicals to form covalent species, second when growing radicals react reversibly with covalent ... |
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