Stimuli-responsive polymer

K Ishihara. Synthesis of stimuli responsive polymers and their biomedical applications. PhD Thesis, Waseda Univ, Japan, 1986. 

Wax Crystal Control Nanocomposites Stimuli-Responsive Polymers... 

Reports of building up two-dimensional polymers have been published by several research groups [9-12]. Additional reports [13-15] and a review [16] have appeared on stimuli-responsive polymer gels and their application to chemomechanical systems. The preparation and application of new monosized polymer particles have been reviewed [17]. 

Several attempts have been made to construct stimuli-responsive polymer solution and gel systems which undergo isothermal phase transitions by external stimulation, such as photons or chemicals. Aqueous solutions of poly(A -isopropylacrylamide) having photoisomerizable chromophores or host molecules in the pendant groups showed reversible phase separations by photoirradiation or by the addition of specific metal or ammonium ions. The gels made of the polymers also underwent photostimulated or chemical-induced volume phase transitions. 

The conformation of polymers governs their various physicochemical properties. When the conformation is reversibly controlled by external stimulation, such as photons, or chemicals, the conformation change should produce a concomitant change in polymer properties in solution as well as in the gel. Polymers which change their properties reversibly by such external stimulation may be referred to as stimuli-responsive polymers. 

The phase transitions, such as a phase separation of polymer solutions, a sol-gel transition, or a volume phase transition of gels, are always accompanied by conformation changes of polymers. Therefore, when the phase transitions are induced isothermally by external stimulation, the transitions cause efficient conformation changes. This contribution describes how such efficient stimuli-responsive polymer systems can be constructed. 

Figure la shows a general schematic illustration of the stimuli-responsive phase transition of a polymer system from the state X to the state Y. In the absence of external stimulation, the polymer system changes the state at a temperature Ta. We assume that the phase transition temperature will rise to Tb in the presence of external stimulation. Then, if the external stimulation is applied to the system at T (T, < T < Tb), the state will change from Y to X isothermally at a certain value of the external stimulation, Ca as shown in Fig. lb. This principle is useful for constructing efficient stimuli-responsive polymers. 

The concept of photostimulated and chemical-induced phase transitions described in this chapter can be applied to other systems, such as proton-induced or electrochemical phase transitions. All of these systems have high energy conversion efficiency in principle and the stimuli-responsive polymer systems are sensitive. A serious disadvantage of these systems is that the working temperature is limited to a rather narrow range near the phase transition of the parent polymer. This point should be kept in mind when used in practice. 

Nath, N., and Chilkoti, A. (2002). Creating smart surfaces using stimuli responsive polymers Adv. Mat. Proc. 14, 1243-1247. 

CdLH A, Pennadam S, Alexander C (2005) Stimuli responsive polymers for biomedical applications. Chem Soc Rev 34 276-285... 

It should be also noted that the field of smart polymer surfaces is not limited to the macromolecular structures presented in the first part of this chapter. Although some classic stimuli-responsive polymers such as PNIPAM or poly(acrylic acid) have been studied for several years, new exciting options are reported every week in the polymer literature. For instance, the synthesis of chemo- and bioresponsive polymers is a topic in full expansion [9], Thus, new developments in the fields of bioassays and biosensors may be expected in the near future. For instance, more advanced surface concepts (e.g., multiresponsive behaviors, signal cascades) can be anticipated with reasonable certainty. 

When a molecular recognition host and a stimuli-responsive polymer are integrated in the same material, a novel function can be achieved in the combined compound that is different from the component materials. 

Costa, F. R., Saphiannikova, M., Wagenknecht, U., and Heinrich, G., Layered double hydroxide based polymer nanocomposites, Adv. Polym. Sci. (2008), 210(Wax Crystal Control Nanocomposites Stimuli-Responsive Polymers), 101-168. 

The synthesis of stimuli-responsive polymer gel microspheres have been receiving growing attention [67-69,73]. Polymer microspheres that combine both temperature- and pH-responsive volume phase transitions have been elaborated, as reported by many authors [2,5-7,65,66]. Owing to their relatively rapid and easy magnetic separation, thermosensitive polymer magnetic microspheres could be widely used in biomedical and bioengineering, such... 

---