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Internal nanoparticle structure of temperature-responsive self-assembled PNIPAM-b-PEG-b-PNIPAM triblock copolymers in aqueous solutions: NMR, SANS and light scattering studies
In this study we report detailed information on the internal structure of PNIPAM-b-PEG-b-PNIPAM nanoparticles formed from self-assembly in aqueous solutions upon increase in temperature. NMR spectroscopy, light scattering and small-angle neutron scattering (SANS) were used to monitor different stages of nanoparticle formation as a function of temperature, providing insight into the fundamental processes involved. The presence of PEG in a copolymer structure significantly affects the formation of nanoparticles, making their transition to occur over a broader temperature range. The crucial parameter that controls the transition is the ratio of PEG/PNIPAM. For pure PNIPAM, the transition is sharp; the higher the PEG/PNIPAM ratio results in a broader transition. This behavior is explained by different mechanisms of PNIPAM block incorporation during nanoparticle formation at different PEG/PNIPAM ratios. Contrast variation experiments using SANS show that the structure of nanoparticles above cloud point temperatures for PNIPAM-b-PEG-b-PNIPAM copolymers is drastically different from the structure of PNIPAM mesoglobules. In contrast with pure PNIPAM mesoglobules, where solid-like particles and chain network with a mesh size of 1-3 nm are present; nanoparticles formed from PNIPAM-b-PEG-b-PNIPAM copolymers have non-uniform structure with “frozen” areas interconnected by single chains in Gaussian conformation. SANS data with deuterated “invisible” PEG blocks imply that PEG is uniformly distributed inside of a nanoparticle. It is kinetically flexible PEG blocks which affect the nanoparticle formation by prevention of PNIPAM microphase separation
Glycogen-graft-poly(2-alkyl-2-oxazolines) - the new versatile biopolymer-based thermoresponsive macromolecular toolbox
Internal Nanoparticle Structure of Temperature-Responsive Self-Assembled PNIPAM‑<i>b</i>‑PEG‑<i>b</i>‑PNIPAM Triblock Copolymers in Aqueous Solutions: NMR, SANS, and Light Scattering Studies
In
this study, we report detailed information on the internal structure
of PNIPAM-<i>b</i>-PEG-<i>b</i>-PNIPAM nanoparticles
formed from self-assembly in aqueous solutions upon increase in temperature.
NMR spectroscopy, light scattering, and small-angle neutron scattering
(SANS) were used to monitor different stages of nanoparticle formation
as a function of temperature, providing insight into the fundamental
processes involved. The presence of PEG in a copolymer structure significantly
affects the formation of nanoparticles, making their transition to
occur over a broader temperature range. The crucial parameter that
controls the transition is the ratio of PEG/PNIPAM. For pure PNIPAM,
the transition is sharp; the higher the PEG/PNIPAM ratio results in
a broader transition. This behavior is explained by different mechanisms
of PNIPAM block incorporation during nanoparticle formation at different
PEG/PNIPAM ratios. Contrast variation experiments using SANS show
that the structure of nanoparticles above cloud point temperatures
for PNIPAM-<i>b</i>-PEG-<i>b</i>-PNIPAM copolymers
is drastically different from the structure of PNIPAM mesoglobules.
In contrast with pure PNIPAM mesoglobules, where solidlike particles
and chain network with a mesh size of 1–3 nm are present, nanoparticles
formed from PNIPAM-<i>b</i>-PEG-<i>b</i>-PNIPAM
copolymers have nonuniform structure with “frozen” areas
interconnected by single chains in Gaussian conformation. SANS data
with deuterated “invisible” PEG blocks imply that PEG
is uniformly distributed inside of a nanoparticle. It is kinetically
flexible PEG blocks which affect the nanoparticle formation by prevention
of PNIPAM microphase separation