Thermoresponsive

Materials that typify thermoresponsive behavior are polyethylene—poly (ethylene glycol) copolymers that are used to functionalize the surfaces of polyethylene films (smart surfaces) (20). When the copolymer is immersed in water, the poly(ethylene glycol) functionaUties at the surfaces have solvation behavior similar to poly(ethylene glycol) itself. The abiUty to design a smart surface in these cases is based on the observed behavior of inverse temperature-dependent solubiUty of poly(alkene oxide)s in water. The behavior is used to produce surface-modified polymers that reversibly change their hydrophilicity and solvation with changes in temperatures. Similar behaviors have been observed as a function of changes in pH (21—24). 

Keywords Colloidal stability Globule Mesoglobule Thermoresponsive polymers Abbreviations... 

In the researches performed by Tenhu and co-authors [19-21], it was shown that by means of chemical modification of the units with reactive pendant groups in thermoresponsive NiPAAm-containing copolymers one can prepare polymeric products, whose solution behaviour resemble in some aspects the behaviour predicted by the theory for protein-like copolymers. Scheme 1 presents the reaction used in these syntheses. 

Water-soluble thermoresponsive PNIPAM and PMVE blocks have been associated to hydrophobic blocks [140,141], Micelles have been prepared in water in which the hydrophobic core is surrounded by PMVE or PNIPAM... 

Deng Y, Wang C, Shen X, Yang W, Jin L, Gao H, Fu S (2005) Preparation, characterization, and application of multistimuli-responsive microspheres with fluorescence-labeled magnetic cores and thermoresponsive shells. Chem Eur J 11 6006-6013... 

In most cases, a suitable molecular modification of the catalyst structure is required to obtain the desired thermoresponsive properties. Polyether and in particular PEG substituents are receiving considerable interest in this field. The present study has addressed structure-activity relationships for well-defined low molecular weight model ligands in the rhodiiun-catalyzed hydroformylation of 1-octene as benchmark reaction. Figure 3 summarizes the observed trends. 

Thermoresponsive Polymeric Micelles for Double Targeted Drug Delivery... 

We have constructed thermoresponsive systems utillizing semitelechelic PIPAAm chains with freely mobile ends, synthesized by telomerization using telogens as a following reaction [6] nM -i- HS-X H-(M)n-S-X. 

We have utilized thermoresponsive properties of PIPAAm and its gels as on-off switches for drug release [6,7], chromatography systems [9-11], and attachment/detachment of cells [12-14] (Scheme 1). Hydrophobic chains of collapsed PIPAAm above its LCST interact with cells and proteins. Although below the LCST, PIPAAms are highly hydrated flexible chains and... 

Schone 1 Thermoresponsive systems constructed using semitelechelic poly(Ai-isopropylacrylamide). 

Scheme 2 Thermoresponsive polymeric micelle structures and fimctions.

In general, incorporation of hydrophobic groups into PIPAAm chains decreases the LCST [29-31]. Hydrophobic groups alter the hydrophilic/ hydrophobic balance in PIPAAm, promoting a PIPAAm phase transition at the LCST, water clusters around the hydrophobic segments are excluded from the hydrophobicaUy aggregated inner core. The resulting isolated hydrophobic micellar core does not directly interfere with outer shell PIPAAm chain dynamics in aqueous media. The PIPAAm chains of the micellar outer shell therefore remain as mobile linear chains in this core-shell micellar structure. As a result, the thermoresponsive properties of PIPAAm in the outer PIPAAm chains of this structure are unaltered [23-27,32]. 

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