Phase behavior of poly(N-isopropylacrylamide) in binary aqueous solutions

Costa, Ricardo O.R.; Freitas, Roberto F. S.

doi:10.1016/s0032-3861(02)00507-4

Cited by 264 publications

(362 citation statements)

References 35 publications

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“…Moreover, the thermal transition should be sharp when very small variations of temperature occur below and above the LCST. As it is well known, poly(NIPAAm) exhibits a LCST value at 32ºC in aqueous solution [4,5]. Under pseudo-physiological conditions (PB at pH 7.4) the LCST decreases to lower temperatures [12].…”

Section: Results and Discussion 31 Preparation And Characterizationmentioning

confidence: 99%

“…Indeed, temperature variations trigger changes of the polymer configuration, leading to the modulation of the release rate of incorporated drugs. Poly(N-isopropylacrylamide) (poly(NIPAAm)) is the most relevant thermoresponsive polymer for biomedical applications, because it possesses a sharp phase transition or a lower critical solution temperature (LCST) around 32ºC in aqueous solutions [4,5]. Below the LCST, the polymer is in the hydrated state and therefore it is soluble.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Lower critical solution temperature versus volume phase transition temperature in thermoresponsive drug delivery systems

Constantin¹,

Cristea²,

Ascenzi³

et al. 2011

Express Polym. Lett.

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Abstract. One of the most subtle problem in the characterization of thermoresponsive polymers is the evaluation of the relationship between the lower critical solution temperature (LCST) of the linear polymer and the volume phase transition temperature (VPTT) of the corresponding hydrogel. Here, the LCST and the onset temperature of linear poly(N-isopropylacrylamide-co-N-hydroxymethyl acrylamide) has been determined under pseudo-physiological conditions by cloud point (CP) measurements and by microcalorimetric analysis. The LCSTs, as well as the onset temperatures, determined by the CP method, decrease with increasing the concentration of the polymer solution. On the contrary, microcalorimetric analyses give almost the same values for LCSTs and the onset temperatures regardless of polymer concentration. The VPTT of the hydrogel, determined by the blue dextran method, was found to be closely similar to the LCST of the concentrated polymer solution (10%, w/v), determined by the CP method. In fact, the hydrogel could be considered as a concentrated polymer solution whose concentration could be related to the amount of water retained by the hydrogel. Hydrogel microspheres have been also reported to release diclofenac, a drug model system, in a pulsating way at temperatures slightly below and above the VPTT.

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Section: Results and Discussion 31 Preparation And Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Lower critical solution temperature versus volume phase transition temperature in thermoresponsive drug delivery systems

Constantin¹,

Cristea²,

Ascenzi³

et al. 2011

Express Polym. Lett.

View full text Add to dashboard Cite

show abstract

“…The majority of such temperature induced solubility transitions are based on the lower critical solution temperature (LCST) behavior of polymers in aqueous solution, i.e., the polymer is dissolved at low temperature by favorable hydration while increasing the temperature leads to an entropy driven dehydration resulting in a collapse of the hydrophobic polymer chains [18,21,23]. Polymers exhibiting the opposite upper critical solution temperature (UCST) behavior in aqueous solutions, i.e., insoluble at low temperatures and soluble at elevated temperatures, are much less common [24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Temperature Induced Solubility Transitions of Various Poly(2-oxazoline)s in Ethanol-Water Solvent Mixtures

et al. 2010

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Abstract:The solution behavior of a series of poly(2-oxazoline)s with different side chains, namely methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, nonyl, phenyl and benzyl, are reported in ethanol-water solvent mixtures based on turbidimetry investigations. The LCST transitions of poly(2-oxazoline)s with propyl side chains and the UCST transitions of the poly(2-oxazoline)s with more hydrophobic side chains are discussed in relation to the ethanol-water solvent composition and structure. The poly(2-alkyl-2-oxazoline)s with side chains longer than propyl only dissolved during the first heating run, which is discussed and correlated to the melting transition of the polymers.

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“…It is well documented that the LCST of PNIPAm is $32 C, [59][60][61][62] close to physiological temperature. Although varying the degree of polymerization, 63 and topology, 64 offers some degree of control and tunability of the LCST in NIPAm homopolymers; for materials with low molecular weights, the effect on the LCST of end-groups can become important.…”

Section: (B)mentioning

confidence: 99%

Sequential thiol‐ene/thiol‐ene and thiol‐ene/thiol‐yne reactions as a route to well‐defined mono and bis end‐functionalized poly(N‐isopropylacrylamide)

Chan

Hoyle

et al. 2009

J. Polym. Sci. A Polym. Chem.

211

191

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Sequential thiol-ene/thiol-ene and thiol-ene/thiol-yne reactions have been used as a facile and quantitative method for modifying end-groups on an N-isopropylacrylamide (NIPAm) homopolymer. A well-defined precursor of polyNIPAm (PNIPAm) was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization in DMF at 70 C using the 1-cyano-1-methylethyl dithiobenzoate/2,2 0 -azobis(2-methylpropionitrile) chain transfer agent/initiator combination yielding a homopolymer with an absolute molecular weight of 5880 and polydispersity index of 1.18. The dithiobenzoate end-groups were modified in a one-pot process via primary amine cleavage followed by phosphine-mediated nucleophilic thiol-ene click reactions with either allyl methacrylate or propargyl acrylate yielding ene and yne terminal PNIPAm homopolymers quantitatively. The ene and yne groups were then modified, quantitatively as determined by 1 H NMR spectroscopy, via radical thiol-ene and radical thiol-yne reactions with three representative commercially available thiols yielding the mono and bis end functional NIPAm homopolymers. This is the first time such sequential thiol-ene/thiol-ene and thiol-ene/thiol-yne reactions have been used in polymer synthesis/end-group modification. The lower critical solution temperatures (LCST) were then determined for all PNIPAm homopolymers using a combination of optical measurements and dynamic light scattering. It is shown that the LCST varies depending on the chemical nature of the end-groups with measured values lying in the range 26-35 C.

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Phase behavior of poly(N-isopropylacrylamide) in binary aqueous solutions

Cited by 264 publications

References 35 publications

Lower critical solution temperature versus volume phase transition temperature in thermoresponsive drug delivery systems

Lower critical solution temperature versus volume phase transition temperature in thermoresponsive drug delivery systems

Temperature Induced Solubility Transitions of Various Poly(2-oxazoline)s in Ethanol-Water Solvent Mixtures

Sequential thiol‐ene/thiol‐ene and thiol‐ene/thiol‐yne reactions as a route to well‐defined mono and bis end‐functionalized poly(N‐isopropylacrylamide)

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