Thermosensitive polymer

One of the oldest and well-known thermosensitive polymers is poly(N-isopropyl acrylamide) (PNIPAm), consisting of hydrophilic (amide) and hydrophobic (isopropyl) groups on an aliphatic carbon backbone. PNIPAm has well-investigated LCST properties [154] and has been proposed for a host of applications, including its use in biomedicine [155]. Another commonly used group include pluronics [156], also known under the nonproprietary name poloxamers , which commonly consist of triblock copolymers of PEO and PPO, the ratio of which determines the HLB. 

Some of the micellar and polymersome structures based on poly(organo)phosphazenes discussed in Section 1.5.4, which by their nature are amphiphilic, have also been reported to show thermosensitive behaviour, that is to aggregate into nanoscale structures upon surpassing their LCST in water. For example, 

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A Gutowska, YH Bae, H Jacobs, J Feijen, SW Kim. Heparin release from thermosensitive polymer coatings In vivo studies. J Biomed Mater Research 29 811-815, 1995. 

Table 7 Summary of the reaction conditions in the synthesis of fluorescently labelled thermosensitive polymers [181]... 

Polymers Responsive to Artificial Stimuli 6.1 Thermosensitive Polymers... 

C. Alexander, D. Gorecki, and P. Caliceti. Physico-Chemical and Pharmacokinetic Studies of Avidin Bioconjugates with Thermosensitive Polymers, 5th International Symposium on Controlled Release of Bioactive Materials, June 21-24, 1998,... 

Abstract A concept of amphiphilicity in application to monomer units of water-soluble polymers is presented. Molecular simulation and experimental studies of polymers consisting of amphiphilic monomers units are reviewed. Those polymers reveal unusual conformational behavior in aqueous solutions forming nanostructures of nonspherical shape. Self-association of amphiphilic thermosensitive polymers in water solutions is discussed. Possibilities for the use of thermosensitive copolymers as catalysts are described. The sharp water-organic boundaries formed by polymer associates in water solutions are shown to be a prospective medium for catalysis owing to adsorption of interfacially active substrates at the interface. 

The properties associated with the amphiphilic monomer units are strongly exemplified in thermosensitive water-soluble polymers, typical examples of which are shown in Scheme 5. Thermosensitive polymers possess a lower critical solution temperature (LCST) in water solutions. Due to their sharp response to temperature variation, they are widely used in various scientific and technological applications. Drug and gene delivery [1-3], chromatographic [9,10], membrane technology [11,12], and catalyst immobiliza-... 

Scheme5 Typical thermosensitive polymers a poly(AT-isopropylacrylamide), b poly(AT-vinylcaprolactam)...

A new way of obtaining nanostructures in systems of thermosensitive polymers by combining them with hydrophilic species was proposed by Bron-stein et al. [54]. The core-shell nanoparticles were obtained by stabilization of the globular conformation of PVCL in aqueous solutions at 45 °C on add-... 

Some works were reported in which thermosensitive polymers were conjugated with hydrophobic groups. End-capping random poly(NIPA-co-dimethylacrylamide) [55] and grafting poly(NIPA-co-hydroxymethylacryl-amide) [56] with cholesterol moieties led to self-associating polymers with different morphologies. By dissolution of the copolymers in dimethylfor-... 

As a conclusion to this part, one may state that thermosensitive polymers represent prospective macromolecules for the design of nanoparticles the... 

Furthermore, Fu et al.140 developed a transport system that responds to thermal stimuli. This system is based on chains of poly-iV-isopropylacrylamide (a known thermosensitive polymer), which exists in a collapsed, hydrophobic state when exposed to heat, but in an expanded, hydrophilic state in the cold. In this way, samples of mesoporous, spherical silica particles (particle diameter 10 p,m) that were lined and coated with the thermosensitive polymer by atom transfer radical polymerization... 

In addition, temperature-responsive properties of PNIPAAm have also been used in fabricating molecular ion gating membranes.37 38 In these studies, the concept of an ion gating molecular recognition membrane using synthetic host substances and a thermosensitive polymer was proposed. Figure 15.1038 illustrates the concept. The membrane was prepared by plasma graft copolymerization, which filled the pores of a porous polyethylene him with a copolymer of A -isopropyl... 

Figure 15.10 Schematic representation of a molecular recognition ion gating membrane. The copolymer of thermosensitive polymer fV-isopropylacrylamide, and crown ether polymer, BCAm, is grafted on the pore surface. The membrane senses a specific ion Mn+, by the crown receptor, and closes its pores rapidly.38 (Reprinted with permission from T. Ito et al., J. Am. Chem. Soc. 2002,124,7840—7846. Copyright 2002 American Chemical Society.)...

Poly(N-isopropylacrylamide) (PNIPAM) is the most studied thermosensitive polymer in aqueous media. It is soluble in water at low temperatures but becomes insoluble when the temperature is increased above a certain temperature ( 32 °C) (lower critical solution temperature), which is related to the coil-to-globule transition [64, 65]. In the case of a polymer network, a volume change occurs reversibly within a narrow temperature range. The properties of such microgels can be varied to a great extent by the introduction... 

In the meantime, this phenomenon has also been observed by other groups for thermosensitive polymer-based metal nanoparticles [77, 78]. Pich et al. have used microgel particles based on the copolymer of A-vinylcaprolactam (VCL) and ace-toacetoxyethyl methacrylate (AAEM) (PVCL/PAAEM) as the carrier system for the deposition of metal nanoparticles. The microgels were first modified with poly(3,4-ethylenedioxythiophene) (PEDOT) nanorods through an in situ oxidative polymerization process. Microgels with PEDOT nanorods in the shell were then used for the... 

Kono, K. (2001), Thermosensitive polymer-modified liposomes, Adv. Drug Deliv. Rev., 53,307-319. 

Thermosensitive polyphosphazenes with (o-methoxy poly(ethylene glycol) in combination with glycine ethyl ester and depsipeptide ethyl ester or al-kylamines as substituents have been synthesized and characterized. All polymers exhibit LCST properties. Thermosensitive polymers have also been prepared by the introduction of a-amino-co-methoxy- poly(ethylene glycol) and L-isoleucine ethyl ester substituents to the phosphazene backbone. Polymer (230) shows reversible sol-gel transitions in aqueous solution depending on the temperature of the solution. ... 

Trialkyl-4-vinylbenzyl phosphonium chloride/ V-isopropylacrylamide (NIP AAm) copolymers. These types of crosslinked TRVB/NIPAAm copolymers were prepared by copolymerization of TRVB, NIP AAm, and MBAAm in dimethyl sulfoxide. Poly(NIPAAm) is a thermosensitive polymer, which has a lower critical solution temperature (LCST) at around 33°C. Therefore, the copolymers are crosslinked cationic polymers and thermosensitive polymers, which swell and deswell below and above the LCST (about 33°C) of poly(NIPAAm). 

Shamim, N. et al.. Thermosensitive-polymer-coated magnetic nanoparticles Adsorption and desorption of bovine serum albumin, J. Colloid Interf. Sci., 304,1, 2006. 

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