|223. Costioli, M.D.; Berdat, D.; Freitag, R.; André, X.; Müller, A.H.E.: Investigation of the telomerisation kinetics of N-isopropylacrylamide using 3-mercaptopropionic hydrazide as chain transfer agent , Macromolecules 38, 3630, published on the Web on April 09, 2005 (2005) -- DOI: 10.1021/ma0484882 S0024-9297(04)08488-8|
The telomerization (chain transfer polymerization) kinetics of N-isopropylacrylamide were investigated in various (hydro)organic solvents using 3-mercaptopropionic hydrazide as chain transfer agent (telogen). Except for the dioxane/water system telogen consumption rates were similar for all cases, while solvent effects could be observed for the monomer consumption rates. Chain transfer constants, as defined by the ratio of the rate constants for chain transfer and chain propagation (CT = ktr,/kp), were highest in DMF (10.3), a solvent unable to form hydrogen bonds or dipole-dipole interactions with the monomer, while a more promising value of CT = 1.7 was found for the 6:4 methanol/water mixture. The highest monomer consumption rates were observed for the 1:1 dioxane/water mixture. However, in this particular case the telogen consumption was also found to increase, as we propose due to a "hydrophobic effect" whereby polymer microaggregates serve to locally increase the concentration of telogen and/or monomer once a certain water concentration has been passed. As a result a comparatively high CT of 3.2 characterizes the dioxane/water system.