title: Stereoblock copolymers and tacticity control in controlled/living radical polymerization.
abstract: Three controlled/living radical polymerization processes, atom transfer radical polymerization (ATRP), reversible addition-fragmentation transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), were investigated for the polymerization of N,N-dimethylacrylamide in the presence of Lewis acids known to enhance isotacticity, such as yttrium trifluoromethanesulfonate (Y(OTf)(3)) and ytterbium trifluoromethanesulfonate (Yb(OTf)(3)). Poly(N,N-dimethylacrylamide) with controlled molecular weight, low polydispersity (M(w)/M(n) < 1.2), and a high proportion of meso dyads ( approximately 85%) was prepared by ATRP (with initiating system methyl 2-chloropropionate/CuCl/Me(6)TREN) and RAFT (with cumyl dithiobenzoate transfer agent) in the presence of Y(OTf)(3). The combination of NMP (using N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, SG1) and a Lewis acid complexation technique led to less precise control over chain architecture and microstructure ( approximately 65% meso dyads), as compared to RAFT/Y(OTf)(3) or ATRP/Y(OTf)(3). The latter two systems were used for the first one-pot synthesis of stereoblock copolymers by radical polymerization. Well-defined stereoblock copolymers, atactic-b-isotactic poly(N,N-dimethylacrylamides), were obtained by adding Y(OTf)(3) at a given time to either RAFT or ATRP polymerizations, initially started without the presence of the Lewis acid.
authors.affiliation: Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Lutz
authors.forename: Dorota
authors.initials: D
authors.lastname: Neugebauer
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Matyjaszewski
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008698:Mesylates / Q000737:chemistry; D008958:Models, Molecular; D008970:Molecular Weight; D009589:Nitrogen Oxides / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D015019:Yttrium / Q000737:chemistry
chemical_list: D000178:Acrylamides; D008698:Mesylates; D009589:Nitrogen Oxides; C429790:poly(N,N-dimethylacrylamide); D015019:Yttrium; C099046:N,N-dimethylacrylamide; C039900:nitroxyl; C012077:trifluoromethanesulfonic acid