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Numerous non-ionic thermally responsive homopolymers phase separate from their aqueous solutions upon heating. Far fewer neutral homopolymers are known to phase separate upon cooling. A systematic compilation of the polymers reported to exhibit thermoresponsive behaviour is presented in this review, including N-substituted poly[(meth)acrylamide]s, poly(N-vinylamide)s, poly(oxazoline)s, protein-related polymers, poly(ether)s, polymers based on amphiphilic balance, and elastin-like synthetic polymers. Basic properties of aqueous solutions of these polymers are briefly described.

The use of various functionalized polymers as stabilizers to design metal core-organic shell hybrid nanoparticle architectures has attracted increasing interest for different applications. The feature article reviews recent reports published from 2004 to the beginning of 2007 on the synthesis of polymer protected gold nanoparticles (AuNPs), and also comments their properties and applications.

This work focuses on the synthesis method of Au nanoparticles protected by a well-defined polymer monolayer. Nanosized, spherical gold clusters coated with poly(N-isopropylacrylamide) (PNIPA) grafts were prepared by controlled radical polymerization. The polymerization of N-isopropylacrylamide was initiated from the surface of a gold nanoparticle modified with 4-cyanopentanoic acid dithiobenzoate for a reversible-addition-fragmentation chain-transfer polymerization. The number mean diameter of the Au core was 3.2 nm as observed by high-resolution transmission electron microscopy. The molar mass of the PNIPA ligand was 21000 g/mol by gel permeation chromatography. The changes in the surface plasmon of gold were investigated in different media, and as functions of particle concentration, as well as of temperature in aqueous solutions. The particles were soluble at least slightly in water, forming aggregates. The area and the maximum wavelength of the plasmon band in water decreased with dilution and increasing temperature. During the collapse of PNIPA ligands the surroundings of the gold surface change from hydrophilic to hydrophobic.

In this mini-review, we discuss multi-stimuli-responsive polymers, which exhibit upper critical solution temperature (UCST) behavior mainly in aqueous solutions, and focus on examples where counter ions, electricity, light, or pH influence the thermoresponsiveness of these polymers.