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Density and viscosity as real-time probes for progress of high-pressure polymerizations / Kun Liu in Industrial & engineering chemistry research, Vol. 47 n°15 (Août 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 n°15 (Août 2008) . - p. 5039–5047 Titre : Density and viscosity as real-time probes for progress of high-pressure polymerizations : polymerization of Methyl Methacrylate in Acetone Type de document : texte imprimé Auteurs : Kun Liu, Auteur ; Erdogan Kiran, Auteur Année de publication : 2008 Article en page(s) : p. 5039–5047 Note générale : Bibliogr. p. 5047 Langues : Anglais (eng) Mots-clés : Acetone  --  methyl  methacrylate  PolymerizationModel  mixtures  --  densityModel  mixtures  --  viscosity Résumé : Density and viscosity have been used as real-time probes to follow the progress of free-radical polymerization of methyl methacrylate in acetone at high pressures. Specifically, the polymerizations were conducted at 343 K and at 7, 14, 21, 28, 35, and 42 MPa in acetone with AIBN as initiator. Polymers with narrow molecular-weight distributions (Mw/Mn = 1.45–1.55) and without high-molecular-weight tail-ends (Mz/Mw = 1.26–1.33) were formed. The results show that the polymerization proceeds in two distinguishable regimes characterized by different rates of change in density or viscosity. The densities and viscosities of model mixtures of poly(methyl methacrylate) plus methyl methacrylate (the monomer) of known compositions were also measured and used to relate the change in viscosity during polymerization to change in the monomer concentration. The change in monomer concentration was then used in evaluating the rate constant and its pressure dependence. The overall apparent first-order rate constants were found to be in the range 0.002−0.004 min−1 at 7 MPa and 0.006−0.008 min−1 at 42 MPa. The reductions in the time rate of change in density and viscosity are discussed in terms of the polymer concentration and viscosity, reaching levels that can be associated with the chain-overlap concentrations; this leads to the onset of diffusional limitations for macroradicals in solution polymerizations even when the viscosities remain low, around 1 mPa s. The low polydispersities and the absence of high-molecular-weight tailing were interpreted in terms of termination by combination involving “short”−“long” coupling of macroradicals. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie0716621 [article] Density and viscosity as real-time probes for progress of high-pressure polymerizations : polymerization of Methyl Methacrylate in Acetone [texte imprimé] / Kun Liu, Auteur ; Erdogan Kiran, Auteur . - 2008 . - p. 5039–5047. Bibliogr. p. 5047 Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 n°15 (Août 2008) . - p. 5039–5047 Mots-clés : Acetone  --  methyl  methacrylate  PolymerizationModel  mixtures  --  densityModel  mixtures  --  viscosity Résumé : Density and viscosity have been used as real-time probes to follow the progress of free-radical polymerization of methyl methacrylate in acetone at high pressures. Specifically, the polymerizations were conducted at 343 K and at 7, 14, 21, 28, 35, and 42 MPa in acetone with AIBN as initiator. Polymers with narrow molecular-weight distributions (Mw/Mn = 1.45–1.55) and without high-molecular-weight tail-ends (Mz/Mw = 1.26–1.33) were formed. The results show that the polymerization proceeds in two distinguishable regimes characterized by different rates of change in density or viscosity. The densities and viscosities of model mixtures of poly(methyl methacrylate) plus methyl methacrylate (the monomer) of known compositions were also measured and used to relate the change in viscosity during polymerization to change in the monomer concentration. The change in monomer concentration was then used in evaluating the rate constant and its pressure dependence. The overall apparent first-order rate constants were found to be in the range 0.002−0.004 min−1 at 7 MPa and 0.006−0.008 min−1 at 42 MPa. The reductions in the time rate of change in density and viscosity are discussed in terms of the polymer concentration and viscosity, reaching levels that can be associated with the chain-overlap concentrations; this leads to the onset of diffusional limitations for macroradicals in solution polymerizations even when the viscosities remain low, around 1 mPa s. The low polydispersities and the absence of high-molecular-weight tailing were interpreted in terms of termination by combination involving “short”−“long” coupling of macroradicals. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie0716621