Poly N-isopropylacrylamide

A number of investigations on the thermal volume transition of PNIPAM have been performed [201-208]. PNIPAM chains carry two types of bound 

Data gathered by microcalorimetry, specifically changes in the partial heat capacity, Cp(r), of a polymer solution at temperatures below and above 

Kujawa and Winnik [209] reported recently that other volumetric properties of dilute PNIPAM solutions can be derived easily from pressure perturbation calorimetry (PPG), a technique that measures the heat absorbed or released by a solution owing to a sudden pressure change at constant temperature. This heat can be used to calculate the coefficient of thermal expansion of the solute and its temperature dependence. These data can be exploited to obtain the changes in the volume of the solvation layer around a polymer chain before and after a phase transition [210], as discussed in more detail in the case of PVCL in Sect. 3.2.2. 

The reluctance of single PNIPAM globules to aggregate at elevated temperature may be ascribed quahtatively to the low probability of encounter of 

The following mechanism emerges form the observation reported so far on the colloidal stability of multichain PNIPAM particles at elevated temperature. Let us note first that such PNIPAM particles are examples of mesoglobules, according to the definition of Timoshenko and Kuznetsov [215]  

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Hofkens, J., Hotta, J., Sasaki, K., Masuhara, H. and Iwai, K. (1997) Molecular assembling by the radiation pressure of a focused laser beam Poly (N-isopropylacrylamide) in aqueous solution. Langmuir, 13, 414-419. 

Irk, Af. Stimuli-Responsive Poly(N-isopropylacrylamide), Photo- and Chemical-Induced Phase Transitions. VoL 110, pp. 49-66. 

Liang, D., Zhou, S., Song, L., Zaitsev, V. S., and Chu, B., Copolymers of poly(N-isopropylacrylamide) densely grafted with poly(ethylene oxide) as high-performance separation matrix of DNA, Macromolecules, 32, 6326, 1999. 

BG Kabra, SH Gehrke. Synthesis of fast response poly(N-isopropylacrylamide) gels. Polym Commun 32 322-323, 1991. 

R Kishi, O Hirasa, H Ichijo. Fast responsive poly(N-isopropylacrylamide) hydrogels prepared by gamma-ray irradiation. Polym Gels Networks 5 145-151, 1997. 

Table 1 Characteristics of graft copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) [165-167,170]...

Bergbreiter reported that poly(N-isopropylacrylamide)-bound phosphine ligands (PNIPAM-resins) coordinated with the Pd(0) moieties afford efficient catalysts (46) for the Heck, Suzuki and sp-sp cross-coupling reactions (Scheme 4.30) [122]. 

Scheme 5 Polyvalent hydrogen bonding of a a soluble poly(N-isopropylacrylamide) to a 3-PAA/PE hyperbranched graft or b a soluble poly(acrylic acid) to a hyperbranched poly(Ar-isopropylacrylamide) graft on PE...

Poly(N-isopropylacrylamide) (polyNIPAAM), formed by a free radical polymerization of N-isopropylacrylamide, is a water soluble, temperature sensitive polymer. In aqueous solution, it exhibits a lower critical solution temperature (LCST) in the range of 30-35 C depending on the concentration and the chain length of the polymer. Thus, as the solution temperature is raised above the LCST, the polymer undergoes a reversible phase transition characterized by the separation of a solid phase which redissolves when the solution temperature is lowered below the LCST. Its physicochemical properties have been investigated by several laboratories (1-3). 

Considering the rather complicated processes that take place during dissolution it is not surprising that some systems show peculiar behavior. For example, while solubility generally increases with temperature, there are also polymers that exhibit a negative temperature coefficient of solubility in certain solvents. Thus, poly(ethylene oxide), poly(N-isopropylacrylamide), or poly(methyl vinyl ether) dissolve in water at room temperature but precipitate upon warming. This behavior is found for all polymer-solvent systems showing a lower critical solution temperature (LCST). It can be explained by the temperature-dependent... 

Fig. 21 A Schematics of albumin-bound poly(N-isopropylacrylamide) (PNIPAM)-grafted surface via albuminated DC iniferter. B Hypothetical action of temperature-dependent switching of protein desorption by squeezing out and mechanical motion...

Hirotsu, S. Coexistence of Phases and the Nature of First-Order Transition in Poly-N-isopropylacrylamide Gels. Vol. 110, pp. 1-26. 

An anesthetic drug, Richlocaine, developed jointly by scientists from Kazakhstan and Russia, and commercially available biologically active substances bovine serum albumin, lysozyme, and catalase were used. Hydrogels of acrylamide and acrylic acid copolymer(AA-AAc),poly(N-isopropylacrylamide)(PNIPA),N-isopropylacrylamide and acrylic acid copolymer (NlPA-AAc), N-isopropylacrylamide and 2-(acrylamido)-2-propanesulfonic acid copolymer (NIPA-APSA) were synthesized. Diffusion parameters of bioactive substances into hydrogel matrices were calculated using Eq. (19.1) ... 

It is widely known that poly(N-isopropylacrylamide), poly(IPAAm), in water has a lower critical solution temperature (LCST) at 32 °C. LCST was originally observed in PEG solutions a long time ago. Rowlinson et al. [40] (1957) explained the lower consolute temperature for PEG in water in terms of negative entropies. The first paper on the LCST of poly(IPAAm) at about 31 °C was presented by Heskins and Guillet in 1968 [41]. They reported that aqueous solution of poly(IPAAm) showed phase separation above this temperature, and ascribed it primarily to an entropy effect on the basis of thermodynamical considerations. 

Blood compatibility of PEG-modified surfaces was discussed in terms of the mobility of water molecules at the interface of hydrogel materices. The property and application of poly(N-isopropylacrylamide) and its copolymers as thermoresponsive hydrogel were also reviewed. 

Spherical gold nanoparticles coated with poly(N-isopropylacrylamide) (PNIPAM) grafts have been synthesized by controlled radical polymerization. The polymerization of N-isopropylacrylamide was initiated from the surface of the nanoparticles modified with 4-cyanopentanoic acid dithiobenzoate for reversible addition-fragmentation chain-transfer polymerization. The mean diameter of the Au core was 3.2 nm, as observed by means of high-resolution transmission electron microscopy [90]. 

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