Hydrolytic Susceptibility of Dithioester Chain Transfer Agents and Implications in Aqueous RAFT Polymerizations
The controlled radical polymerization (CRP) technique reversible addition- fragmentation chain transfer (RAFT) has potential for preparing functional (co)polymers directly in an aqueous environment. Hydrolysis and aminolysis can eliminate the active end groups necessary for maintaining "livingness" in water. These reactions have not previously been evaluated with respect to their effect on aqueous RAFT polymerizations. Herein we determine rate constants of hydrolysis and aminolysis for representative water-soluble chain transfer agents (CTAs) cyanopentanoic acid dithiobenzoate (CTP) and the macro-chain-transfer agents (macro-CTAs) of poly(sodium 2-acrylamido- 2-methylpropanesulfonate) (AMPSx) and poly(acrylamide) (AMx) at selected pH values, Rates of hydrolysis and aminolysis both increase with increasing pH and decrease with increasing molecular weight of the dithioester. On the basis of these rate constants, mathematical relationships have been developed to predict the number of living chain ends and the molecular weight with competitive hydrolysis. Utilizing this approach, predictions of molecular weight at specific conversions are in agreement with experimental values determined by SEC/MALLS.
D. B. Thomas et al., "Hydrolytic Susceptibility of Dithioester Chain Transfer Agents and Implications in Aqueous RAFT Polymerizations," Macromolecules, vol. 37, no. 5, pp. 1735-1741, American Chemical Society (ACS), Mar 2004.
The definitive version is available at https://doi.org/10.1021/ma035572t
Materials Science and Engineering
Keywords and Phrases
Chain transfer agents; Controlled radical polymerization (CRP), Copolymers; Esters; Hydrolysis; Monomers; pH effects; Photolysis; Proteins; Rate constants, Polymerization
International Standard Serial Number (ISSN)
Article - Journal
© 2004 American Chemical Society (ACS), All rights reserved.