Effect of Temperature on the Mobility of Core‐Shell‐Type Nanoparticles Composed of Poly(γ‐benzyl‐L‐glutamate) and Poly(N‐isopropylacrylamide)

Abstract

IntroductionPolymers that show phase transition in water upon raising the temperature above a critical point, termed lower critical solution temperature (LCST), have attracted much attention in many areas of modern science and engineering. Among these polymers, poly(N-isopropylacrylamide) (PNIPAAm) is the most popular temperature-sensitive polymer due to its dramatic and reversible transition behavior at around 32 8C. [1,2] Most work on the phase transition of PNIPAAm has so far been limited to the measurements on the macroscopic quantities, although many methods including cloud point measurement, [3] light scattering, [2] DSC, [4] and fluorescence [5] have been used.NMR relaxation times, i.e., spin-lattice relaxation time (T 1 ) and spin-spin relaxation time (T 2 ), and a linewidth give useful information on the microscopic molecular motion of water and polymer in solutions. [6][7][8] Applying NMR technique to study the phase transition of PNIPAAm, Tokuhiro et al. [9] measured T 1 of nonionic and ionic PNIPAAm gels in D 2 O and made a complete interpretation on the dynamics of the side and backbone chains through the phase transition process. In addition, a few researchers reported on the dynamics of PNIPAAm gel, polymer, and water molecules Summary: Core-shell-type nanoparticles composed of PBLG and PNIPAAm were prepared in an attempt to study the effects of temperature on the dynamic behavior of temperature-sensitive polymeric shell, PNIPAAm, in the nanoparticles by 1 H NMR spectroscopy. Spin-lattice relaxation time (T 1 ) and line halfwidth in D 2 O and CDCl 3 were measured to monitor the change of the chain mobility of PNIPAAm in the GN nanoparticles within the temperature range encompassing its LCST. The molecular motion of PBLG segment in GN nanoparticles in CDCl 3 was also examined and compared with that of the PNIPAAm. The morphology, size distribution, and effect of temperature on the sizes of the GN nanoparticles were also investigated. The temperature dependence of T 1 and line halfwidth suggests that the N-isopropyl group turns gradually into the solid-like aggregates at temperatures higher than the LCST of PNIPAAm due to the collapsed coil-globule transition. T 1 values of N-isopropyl groups decreased with increasing PBLG content in GN diblock copolymer, suggesting the mobility of PNIPAAm chain, as the shell, becomes more restricted at higher PBLG core content.Changes in the mobility of PNIPAAm shell in the core-shelltype nanoparticles composed of PBLG and PNIPAAm.

Temperature Behavior of Aqueous Solutions of Poly(2-Oxazoline) Homopolymer and Block Copolymers Investigated by NMR Spectroscopy and Dynamic Light Scattering

“…By diffusion and relaxation time experiments, it is possible to follow changes in molecular motions of polymer and water in solution. Moreover, to clarify conformational problems of macromolecules the 2D 1 H– 1 H NOESY spectra are extremely valuable [ 10 , 29 , 30 , 31 , 32 , 33 ].…”

A Nanogel for Ratiometric Fluorescent Sensing of Intracellular pH Values

“…Furthermore, it was rendered fluorescent by addition of two standard fluorophores that undergo efficient fluorescence resonance energy transfer (FRET) inside the nanogel. The fluorophores coumarin 6 (C6) and Nile Red (NR) were chosen to give a dual (green and red) fluorescent signal that can be easily ratioed.The nanogel (NG) was obtained by a modified reprecipitation method [8] (see the Experimental Section). In essence, an ethanol solution of a hydrogel containing both hydrophilic and hydrophobic domains was dialyzed against water.…”

“…The nanogel (NG) was obtained by a modified reprecipitation method [8] (see the Experimental Section). In essence, an ethanol solution of a hydrogel containing both hydrophilic and hydrophobic domains was dialyzed against water.…”

Thermally Induced Polymeric Assemblies from the PAAc-Based Copolymer Containing Both PNIPAAm and mPEG Grafts in Water

“…T 1 values of the methyl protons of PNIPAAm grafts of the copolymer solution at 10.0 mg/mL increase with increasing temperature even beyond the phase separation region for both runs with different heating modes. On the basis of the relation of T 1 with the correlation time described by the BPP theory, ,, this trend represents a high thermally induced mobility of PNIPAAm grafts residing within the liquidlike interfaces since the T 1 −temperature curve is primarily governed by the product of correction time and Lamor frequency while the latter was kept constant in this study. Although T 1 values of the PNIPAAm methyl protons are abruptly reduced to such extent that these protons become undetectable by 1 H NMR upon transformation of the PNIPAAm segments from the liquidlike to solidlike structure as temperature is increased, the response of T 1 to temperature differs with varying copolymer concentrations and heating methods (Figure A).…”

“…Comparing the two 1 H NMR spectra, a remarkable reduction in the feature signal intensities of PNIPAAm grafts at 50 °C, particularly at δ 1.1 ppm from their methyl protons, suggests the formation of polymeric micelles with hydrophobic cores comprising the solidified PNIPAAm segments to a significant extent. Such a signal intensity reduction is ascribed to a dramatic decrease in the proton spin−lattice relaxation time (T 1 ) upon the solidification of PNIPAAm grafts, thus rendering themselves undetectable in the liquid 1 H NMR measurements. , Nevertheless, this feature signal of PNIPAAm grafts at 1.1 ppm does not disappear completely at 50 °C. On the basis of the fractions detectable and undetectable, a distinct difference in the mobility of PNIPAAm segments that constitute the hydrophobic regions of polymeric assemblies was then clearly illustrated. , The core of polymeric aggregates is thus developed in the form of both liquidlike and solidlike structures.…”