Abstract
Grafting polymer chains on the surface of nanoparticles (NPs) is a strategy used to control the interaction between the NPs and their environment. The fate of the resulting particles in a given environment is strongly influenced by the solvent–polymer interaction. The solvent quality affects the behavior, conformation, and dynamics of the grafted polymer chains. However, when this polymer grafting strategy is used to functionalized polymer particles, the influence of solvent quality becomes even more complex; when the grafted polymer chains and the polymer nanoparticles are tethered together, the effect of the solvent quality on the behavior and dynamics of the system depends on the solvent interaction with both polymer components. To explore the relationship between the solvent quality and the dynamics of polymer-functionalized soft polymer NPs, we designed a system based on cross-linked polystyrene (PS) NPs grafted with a canopy of poly(methyl acrylate) (PMA). PS and PMA, two immiscible polymers, can be selectively solvated by using binary mixtures of solvents. NMR spectroscopy was used to address the effect of those selective solvents on the local mobility of the PS–PMA core-canopy NPs and revealed an interplay between the local mobility of the core and the local mobility of the canopy. A selective reduction of the solvent quality for the PMA canopy resulted in the expected reduction of the local mobility of the PMA chains, but also in the slower dynamics of the PS core. Similarly, a selective reduction of the solvent quality for the PS core resulted in a slower dynamics for both the PS core and the PMA canopy.
Highlights
Nanoparticles functionalized with a canopy of end-tethered polymer chains have been used in a variety of applications, such as drug delivery, adhesives, or coatings.[3−6] Using a canopy of endtethered polymer chains to tune the interactions between the nanoparticles and their environment is a strategy widely employed to control the dispersibility of nanoparticles both in suspension and in polymer matrixes for the formation of nanocomposites with specific properties.[7,8]
Article spectral density function can be used to calculate the correlation time associated with the local dynamics, in the simplest system, for an isotropic rotation, the relation between the local mobility and the spectral density can be expressed by J(ω0) = τr/(1 − ω02τr2)
Albeit the change in solvent quality experienced by the poly(methyl acrylate) (PMA) chains was limited when switching the cosolvent from acetone to cyclohexane, the T2 of the PMA canopy was simultaneously influenced by the large variation in χPS‐solvent, from 0.35 to 0.17, sustained by the PS (Figure S5) resulting in a decrease in the local mobility of the PS core
Summary
The grafting of end-tethered polymer chains on a surface is an excellent strategy to control the properties of interfaces such as the surface of nanoparticles (NPs) in suspension.[1,2] Nanoparticles functionalized with a canopy of end-tethered polymer chains have been used in a variety of applications, such as drug delivery, adhesives, or coatings.[3−6] Using a canopy of endtethered polymer chains to tune the interactions between the nanoparticles and their environment is a strategy widely employed to control the dispersibility of nanoparticles both in suspension and in polymer matrixes for the formation of nanocomposites with specific properties.[7,8] The properties of the resulting functionalized NPs are affected by the chemical composition of the polymer canopy, its architecture, and its interaction with the environment. It can be used to investigate fast relaxation processes associated with the motions, vibrations, and rotation of side groups and it probes the subsegmental and Rouse dynamics of the polymer chains.[25−32] NMR spectroscopy provides results in keeping with other techniques like dielectric spectroscopy or quasielastic neutron scattering[33] with the added benefit of allowing for the analysis of the local dynamics of specific chemical groups without the need for labeling Both NMR spectroscopy and NMR relaxometry have become more popular to characterize polymer functionalized nanoparticles both in the solid-state and in suspension.[34−37]. The protons in the aromatic ring of PS (7.1 to 6.6 ppm) and in the methoxy group (3.7 ppm) were chosen for the analysis
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