PNIPAM- poly

Heterogeneous polymerization Precipitation Emulsion Dispersion PNIPAM microgel nanoparticles Poly(PNIPAM-co-AA) microgel nanoparticles NPs based on poly(butyl methacrylate) core and PNIPAM shell Colloidal nanospheres of poly(butylcyanoacrylate) with a magnetite core Pegylated NPs composed of N,N- diethylacrylamide and N,N-methylene bisacrylamide Berndt et al., 2006 Jones and Lyon, 2000 Gan and Lyon, 2003 Arias et al., 2008 Rieger et al., 2009... 

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]. 

Thus, the PEO segment actually becomes hydrophobic at higher temperatures. This temperature-dependent change converts the amphiphilic block copolymer to a water-insoluble hydrophobic polymer (Topp et al. 1997 Chung et al. 2000). The temperature at which the polymer exhibits this transition is called its lower critical solution temperature (LCST). In addition to PEO, substituted poly(A -isopropyl acrylamide) (PNIPAM Chart 2.1) exhibits temperature sensitivity, where the LCST can be tuned by varying the alkyl fimctionahty. The guest encapsulation combined with the temperature-sensitive precipitation of the polymers has been exploited to sequester and separate guest molecules from aqueous solutions (Fig. 2.4). 

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...

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]. 

Template core-shell particles with cores comprised mainly of poly(glycidyl methacrylate) (GMA) and shells consisting mainly of PNIPAM and amino or thiol-functionalized have been used for the synthesis of Au NPs. The obtained hybrid particles exhibited a reversible color change from red to purple, which originated from the surface plasmon resonance of gold nanoparticles and was temperature-dependent in the range 25-40 °C [96] (Scheme 3.15). 

The effect of phase transitions on ESPT of 2NpOH in poly (/V-isopropy-lacryamide) (PNIPAM) covalently labeled with 2NpOH has been studied [203], The 2NpOH undergoes ESPT at a rate that is dependent on water concentration in aqueous solvent systems. Upon conversion to the phase-separated state in naph-thol-labeled PNIPAM, the efficiency of ESPT diminished, consistent with the formation of a globular phase in which exposure of the probe molecules to the water phase was reduced. 

In this review, hydrophilically and hydrophobically modified poly(N-iso-propylacrylamide) (PNIPAM) copolymers are mainly used to illustrate how amphiphilic copolymer chains can fold from an extended random coil to a collapsed globule in extremely dilute solutions and associate to form a stable mesoglobular phase which exists between single-chain globules and macroscopic precipitation. The copolymers used can be prepared by free-radical reaction. 

Scheme 3 Poly(N-isopropylacrylamide-gra/t-poly(ethylene oxide) (PNIPAM-g-PEO))...

Scheme 5 Poly(N-isopropylacrylamide-co-potassium acrylate) (PNIPAM-co-KAA) and poly(N-isopropylacrylamide-co-sodium acrylate) (PAM-co-NaAA)...

Fig. 21 a Schematic of a linear segmented poly(N-isopropylacrylamide-seg-styrene) (PNIPAM-seg-St) coplymer chain prepared by micelle copolymerization, in which short PS segments are relatively evenly distributed on the chain backbone, b Schematic of the adsorption of a linear PNIPAM-seg-PS chain on a hydrophobic PS substrate in water [97]... 

The comonomer distribution can be alternated by controlling the synthesis conditions, such as the copolymerization at different reaction temperatures at which the thermally sensitive chain backbone has different conformations (extended coil or collapsed globule). In this way, hydrophilic comonomers can be incorporated into the thermally sensitive chain backbone in a more random or more segmented (protein-like) fashion. On the other hand, short segments made of hydrophobic comonomers can be inserted into a hydrophilic chain backbone by micelle polymerization. One of the most convenient ways to control and alternate the degree of amphiphilicity of a copolymer chain, i.e., the solubility difference of different comonomers in a selective solvent, is to use a thermally sensitive polymer as the chain backbone, such as poly(N-isopropylacrylamidc) (PNIPAM) and Poly(N,N-diethylacrylamide) (PDEA). In this way, the incorporation of a hydrophilic or hydrophobic comonomer into a thermally sensitive chain backbone allows us to adjust the degree of amphiphilicity by a temperature variation. 

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