ABSTRACT
Hydrogen-bonding upper critical solution temperature (UCST) thermosensitive nanogels based on poly(N-acryloyl glycinamide) (PNAGA) are synthesized by photo-reversible addition-fragmentation chain transfer mediated polymerization-induced self-assembly (photo-RAFT PISA) in aqueous dispersion using N,N'-methylenebis(acrylamide) as crosslinker and poly(oligo(ethylene glycol) methyl ether acrylate) as both stabilizer and macromolecular chain transfer agent (macro-CTA). Highly stable, spherical nanogels with narrow polydispersity are efficiently produced up to complete monomer conversion within 1 h under UV irradiation at low temperature (3 °C). The thermosensitive behavior of PNAGA-based nanogels, as assessed by dynamic light scattering and UV-vis spectrophotometry, exhibits reversible heating-induced swelling and cooling-induced shrinking corresponding to the expected UCST behavior. The hydrodynamic diameter, swelling ratio, and phase transition temperature of nanogels can be tuned by modifying the initial molar ratio of monomer-to-macro-CTA and the amount of crosslinker in the photo-RAFT PISA of NAGA.
Subject(s)
Hydrogen , Polymers , Nanogels , Polymerization , TemperatureABSTRACT
Synthesis of combs with well-entangled backbones and long branches with high densities has always been a challenge. Steric hindrance frequently leads to coupling of chains and structural imperfections that cannot be easily distinguished by traditional characterization methods. Research studies have therefore tried to use a combination of different methods to obtain more information on the actual microstructures. In this work, a grafting-from approach is used to synthesize poly(n-butyl acrylate) combs using atom transfer radical polymerization (ATRP) in three steps including the synthesis of a backbone, cleavage of protecting groups and growth of side branches. We have compared the linear viscoelastic properties theoretically predicted by a time marching algorithm (TMA) tube based model with the measured rheological behaviour to provide a better insight into the actual microstructure formed during synthesis. For combs with branches smaller than an entanglement, no discernible hierarchical relaxation can be distinguished, while for those with longer branches, a high frequency plateau made by entangled branches can be separated from backbone's relaxation. Dilution of the backbone, after relaxation of side branches, may accelerate the final relaxation, while extra friction can delay it especially for longer branches. Such a comparison provides a better assessment of the microstructure formed in combs.
ABSTRACT
Copolymers of 2-(N,N-dimethylamino)ethyl acrylate (DMAEA) and 2-(tert-Boc-amino)ethyl acrylate (tBocAEA) are synthesized by reversible addition-fragmentation chain transfer polymerization in a controlled manner with defined molar masses and narrow molar masses distributions (Ð ≤ 1.17). Molar compositions of the P(DMAEA-co-tBocAEA) copolymers are assessed by means of 1 H NMR. A complete screening in molar composition is studied from 0% of DMAEA to 100% of DMAEA. Reactivity ratios of both comonomers are determined by the extended Kelen-Tüdos method (r DMAEA = 0.81 and rtBocAEA = 0.99).
Subject(s)
Acrylic Resins/chemistry , Polymers/chemical synthesis , Cations/chemical synthesis , Cations/chemistry , DNA/chemistry , Molecular Structure , Plasmids/chemistry , Polymerization , Polymers/chemistry , Static ElectricityABSTRACT
An attractive concept for designing "smart materials" is the combination of supramolecular interactions with thermoresponsive polymers. Here, this concept is illustrated by preparing aqueous micelles from poly(N-isopropylacrylamide)-block-polystyrene copolymers functionalized at the extremity of their poly(N-isopropylacrylamide) coronal chains by terpyridine ligands. The effect of temperature and of the addition of Zn(II) ions on the self-assembling properties is then studied.
