Laser Light Scattering Study of the Phase Transition of Poly(N-isopropylacrylamide) in Water. 1. Single Chain

Wu, Chi; Zhou, Shuiqin

doi:10.1021/ma00128a056

Cited by 479 publications

(486 citation statements)

References 13 publications

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“…In previous works, we have reported the synthesis and stimuli-responsive micellization behavior of a variety of nonlinear block copolymers including A 2 BA 2 and A 4 BA 4 dumbbell-shaped, 32 AB 4 33 and AB 2 Y-shaped 31,34 star polymers. It is well-known that PNIPAM homopolymer undergoes a coil-to-globule phase transition in dilute aqueous solution above the lower critical solution temperature (LCST) at $32 C. [43][44][45][46][47][48] At temperatures below the LCST, PNIPAM chains adopt a randomly coiled conformation due to the predominantly intermolecular hydrogen bonding interaction between PNIPAM chain segments and water molecules. At temperatures above the LCST, predominant intramolecular hydrogenbonding interactions reduce the water-solubility, accompanied by the collapse and aggregation of PNIPAM chains.…”

mentioning

confidence: 99%

Synthesis of amphiphilic and thermoresponsive ABC miktoarm star terpolymer via a combination of consecutive click reactions and atom transfer radical polymerization

Liu

et al. 2009

J. Polym. Sci. A Polym. Chem.

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Well-defined amphiphilic and thermoresponsive ABC miktoarm star terpolymer consisting of poly(ethylene glycol), poly(tert-butyl methacrylate), and poly(N-isopropylacrylamide) arms, PEG(-b-PtBMA)-b-PNIPAM, was synthesized via a combination of consecutive click reactions and atom transfer radical polymerization (ATRP). Click reaction of monoalkynyl-terminated PEG with a trifunctional core molecule bis(2-azidoethyl)amine, (N 3 ) 2 ANH, afforded difunctional PEG possessing an azido and a secondary amine moiety at the chain end, PEG-NHAN 3 . Next, the amidation of PEG-NHAN 3 with 2-chloropropionyl chloride led to PEG-based ATRP macroinitiator, PEG(AN 3 )ACl. The subsequent ATRP of N-isopropylacrylamide (NIPAM) using PEG(AN 3 )ACl as the macroinitiator led to PEG(AN 3 )-b-PNIPAM bearing an azido moiety at the diblock junction point. Finally, well-defined ABC miktoarm star terpolymer, PEG(-b-PtBMA)-b-PNIPAM, was prepared via the click reaction of PEG(AN 3 )-b-PNIPAM with monoalkynyl-terminated PtBMA. In aqueous solution, the obtained ABC miktoarm star terpolymer self-assembles into micelles consisting of PtBMA cores and hybrid PEG/PNIPAM coronas, which are characterized by dynamic and static laser light scattering, and transmission electron microscopy. On heating above the phase transition temperature of PNIPAM in the hybrid corona, micelles initially formed at lower temperatures undergo further structural rearrangement and fuse into much larger aggregates solely stabilized by PEG coronas.

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mentioning

confidence: 99%

Synthesis of amphiphilic and thermoresponsive ABC miktoarm star terpolymer via a combination of consecutive click reactions and atom transfer radical polymerization

Liu

et al. 2009

J. Polym. Sci. A Polym. Chem.

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“…For HPG-PNIPAM in Figure 7a, /R h S decreases gradually from 75 to 46 nm in the broad temperature range of 20-34 1C and remains constant at 34-36 1C on heating because of the grafted PNIPAM chain shrinking, although it is well known that, for PNIPAM, homopolymer chain /R h S drops sharply in the narrow temperature range of 31-33 1C. 46 Theoretical prediction suggests that strong interchain interactions are present in the brush and cause a broadening of the transition of polymer chains. Our previous works 48,64 and several experimental results [68][69][70][71][72][73][74][75] have already confirmed this prediction.…”

Section: Thermoresponsivity Of Unimolecular Polymeric Micellesmentioning

confidence: 91%

“…46,67 At a temperature below LCST, PNIPAM chains take a random coil conformation because of the predominantly intermolecular hydrogen bonding between PNIPAM chains and water molecules. At a temperature above LCST, intramolecular hydrogenbonding interactions between C¼O and N-H groups render the chains to become compact and collapse, reducing their water solubility.…”

Section: Thermoresponsivity Of Unimolecular Polymeric Micellesmentioning

confidence: 99%

“…[39][40][41] Poly (N-isopropylacrylamide) (PNIPAM) is perhaps the most well-known member of the class of thermoresponsive polymers; it undergoes a phase transition at its lower critical solution temperature (LCST) of 32 1C and has been widely studied as a polymer that is potentially useful for targeted drug delivery, solute separation, tissue culture substrate and controlling the adsorption of proteins. [42][43][44][45][46] You et al 47 have achieved reversible switching between the dendritic hydrophobic core, a second-generation hyperbranched polyester Bolton H20, and the hydrophilic shell by grafting PNIPAM from the terminals of H20. Recently, we have synthesized unimolecular micelles with PNIPAM shell grafting from a hydrophobic fourth-generation hyperbranched polymester H40, and demonstrated their special phase transition behavior.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis of thermoresponsive unimolecular polymeric micelles with a hydrophilic hyperbranched poly(glycidol) core

Luo

Zhang

et al. 2010

Polym J

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This paper describes the reversible phase transition behavior of a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) shell at the surface of a hydrophilic core. Reversible addition-fragmentation transfer (RAFT) polymerization of N-isopropylacrylamide was conducted using a hydrophilic hyperbranched poly(glycidol) (HPG)-based macroRAFT agent. At lower temperatures (o30 1C), the resultant multiarm star block copolymer (HPG-PNIPAM) exists as unimolecular micelles, with hydrophilic HPG as the core and a densely grafted PNIPAM brush as the shell. In laser light scattering (LLS) studies, the concentration used for HPG-PNIPAM is 5Â10 À6 g ml À1 , to avoid any possible aggregation between dendritic unimolecular micelles above the lower critical solution temperature (B32 1C) of PNIPAM. What we observe for the phase transition of HPG-PNIPAM involves only unimolecular process. A combination of dynamic and static LLS studies of HPG-PNIPAM in aqueous solution reveals a reversible phase transition on heating and cooling.

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“…The details of LLS theory and instrumentation can be found elsewhere. [22][23][24] Results and Discussion Figure 1 shows the temperature dependence of the average hydrodynamic radius of the microgels in a dilute solution (6.06 × 10 -5 g/mL). In the temperature range studied, the swelling and shrinking are reversible.…”

Section: Methodsmentioning

confidence: 99%

Nonergodic Dynamics of a Novel Thermally Sensitive Hybrid Gel

Zhao

Zhang

2001

Macromolecules

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As the temperature decreases, the swelling of individual thermally sensitive spherical poly-(N-isopropylacrylamide) microgels in a concentrated dispersion can lead to a sol-gel transition, resulting in a hybrid bulk gel in which individual microgels were physically jam-packed into a three-dimensional network without involving electrostatic interaction, resembling the glass transition of small molecules. The dynamics of such a formed hybrid gel were studied by static and dynamic laser light scattering. Our results showed that the inhomogeneity should be characterized by the difference between the ensemble average scattering intensity and the dynamic component of the time average scattering intensity. The inhomogeneity was strongly dependent on the sol-gel transition rate and the gelling temperature. Our results have also revealed that the inhomogeneity can be completely suppressed if individual swollen microgels are closely packed together, indicating that the static nonergodic behavior originates from large voids formed during the sol-gel transition.

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Laser Light Scattering Study of the Phase Transition of Poly(N-isopropylacrylamide) in Water. 1. Single Chain

Cited by 479 publications

References 13 publications

Synthesis of amphiphilic and thermoresponsive ABC miktoarm star terpolymer via a combination of consecutive click reactions and atom transfer radical polymerization

Synthesis of amphiphilic and thermoresponsive ABC miktoarm star terpolymer via a combination of consecutive click reactions and atom transfer radical polymerization

Synthesis of thermoresponsive unimolecular polymeric micelles with a hydrophilic hyperbranched poly(glycidol) core

Nonergodic Dynamics of a Novel Thermally Sensitive Hybrid Gel

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