Effect of composition and stereoregularity on phase-transition behavior of aqueous N-ethylacrylamide/N-n-propylacrylamide copolymer solutions

Study of the Thermal Phase Transition of Poly(N,N-diethylacrylamide-co-N-ethylacrylamide) Random Copolymers in Aqueous Solution

N-alkyl-substituted polyacrylamides exhibit a thermal coil-to-globule transition in aqueous solution driven by an increase in hydrophobic interactions with rising temperature. With the aim of understanding the role of N-alkyl substituents in the thermal transition, this study focuses on the molecular interactions underlying the phase transition of poly(N,N-diethylacrylamide-co-N-ethylacrylamide) random copolymers. Poly(N,N-diethylacrylamide) (PDEAm), poly(N-ethylacrylamide) (PNEAm), and their random copolymers were synthesized by free radical polymerization and their chemical structure characterized spectroscopically. It was found that the values of the cloud-point temperature increased with PNEAm content, and particle aggregation processes took place, increasing the negative charge density on their surface. The cloud-point temperature of each copolymer decreased with respect to the theoretical values calculated assuming an absence of interactions. It is attributed to the formation of intra- and interchain hydrogen bonding in aqueous solutions. These interactions favor the formation of more hydrophobic macromolecular segments, thereby promoting the cooperative nature of the transition. These results definitively reveal the dominant mechanism occurring during the phase transition in the aqueous solutions of these copolymers.

The effects of cononsolvents on the synthesis of responsive particles via polymerisation-induced thermal self-assembly

Responsive nanogels were synthesised via RAFT-mediated polymerisation-induced thermal self-assembly in cononsolvent mixtures of water and ethanol. The solvent mixture affected the particle size, tacticity and thermal properties.

Molecular dynamics study of the LCST transition in aqueous poly(N-n-propylacrylamide)

The breadth of technological applications of smart polymers relies on the possibility of tuning their molecular structure to respond to external stimuli. In this context, N-substituted acrylamide-based polymers are widely studied thermoresponsive polymers. Poly(N-n-propylacrylamide) (PNnPAm), which is a structural isomer of the poly(N-isopropylacrylamide) (PNIPAm) exhibits however, a lower phase transition in aqueous solution. In this work, we use all-atom molecular dynamics simulations of PNnPAm in aqueous solutions to study, from a microscopic point-of-view, the influence of chain size and concentration on the LCST of PNnPAm. Our analysis shows that the collapse of a single oligomer of PNnPAm upon heating is dependent on the chain length and corresponds to a complex interplay between hydration and intermolecular interactions. Analysis of systems with multiple chains shows an aggregation of PNnPAm chains above the LCST.

Random copolymer gels of N-isopropylacrylamide and N-ethylacrylamide: effect of synthesis solvent compositions on their properties

Random copolymer gels of N-isopropylacrylamide (NIPAM) and N-ethylacrylamide (NEAM) were synthesized using 1 : 1 monomer molar ratio in different methanol–water mixtures. (x_m = 0, 0.06, 0.13, 0.21, 0.31 0.43, 0.57, 0.76, where x_m = mole fraction of methanol) (x_m = 0, 0.06, 0.13, 0.21, 0.31, 0.43, 0.57, 0.76, where x_m = mole fraction of methanol).

Syndiotactic- and heterotactic-specific radical polymerization of N-n-propylmethacrylamide complexed with alkali metal ions

Addition of Li⁺ enhanced the radical polymerization of N-n-propylmethacrylamide, in which the stoichiometry of the monomer–Li⁺ complexes determined the stereospecificity of the radical polymerization.

Hydrogen-bond-assisted isotactic-specific radical polymerization of N-vinyl-2-pyrrolidone with tartrate additives in toluene at low temperatures: high-resolution 1H NMR analysis

Isotactic-rich poly(N-vinyl-2-pyrrolidone) was successfully prepared by radical polymerization of N-vinyl-2-pyrrolidone assisted by diethyl l-tartrate (l-EtTar) at low temperatures.