Temperature sensitive microgels

Different ionic monomers were copolymerized with NIPAAm or VCL to obtain pH- and temperature-sensitive microgels. Snowden et al. [65] reported preparation of aqueous microgels by copolymerization of NIPAAm and acrylic acid (AAc) in a precipitation polymerization process. The AAc content was 5wt%. Obtained microgels displayed pH and electrolyte sensitivity, as well as temperature sensitivity. 

Fig. 5 Synthesis of PVME particles by irradiation of phase-separated solutions. Above the phase transition temperature Tc, the polymer chains collapse to globular aggregates. The collapsed structures are fixed by electron beam irradiation to yield temperature-sensitive microgel particles...

Since Pelton and Chibante reported the synthesis of the first temperature-sensitive microgel from iV-isopropylacrylamide (NIPAM) and crosslinker in 1986 [74], responsive microgels have attracted numerous attempts to explore their potential application in many fields, such as sensing and drug delivery [75]. Now the most extensively studied respruisive microgels are prepared with poly(fV-isopropyla-crylamide) (PNIPAM) [2], It is weU known that the phase transition temperature of PNIPAM is about 32°C [76], When r< LCST, the PNIPAM chain is soluble in water as a random cod. When r LCST, the subtle balance between PNIPAM and water is broken and phase transition occurs [77]. However, the single-molecule level mechanism of the phase transition of PNIPAM had not been proposed until very recently. 

Scattering methods such as SANS, SAXS, as well as DLS and SLS have been applied to temperature-sensitive microgels in several studies. " However, scattering intensity profiles are often investigated in the high-q regime only. In this case, the applied model equations are those of the limiting behavior and do not describe the stmcture of the entire particle. 

Several reports in the literature describe using temperature-sensitive microgel-based films for studies of cell adsorption. Kawaguchi et demonstrated that cells... 

STI Stieger, M. and Richtering, W., Shear-induced phase separation in aqueous polymer solutions Temperature-sensitive microgels and linear polymer chains. 

Influence of Comonomers on Microgel Properties. The overall physicochemical properties of a microgel depend not only on the cross-linker concentration, but also on the concentration of monomer/comonomers used in the synthesis. The addition of a small amount of comonomer (typically 1-5 wt% monomer) can have a dramatic effect on the overall properties of the resultant microgel particles. For example, a pH- and temperature-sensitive microgel can be prepared by copolymerizing poly(NIPAM) with acrylic acid. These spherical particles undergo... 

FIGURE 9.38 Illustration of a temperature-sensitive microgel particle-based drug release process. (From Imaz, A. and Foreada, J., N-Vinylcaprolactam-Based Microgels for Biomedical Applications, Vol. 48, J. Polym. Sci., Part A Polym. Chem., 2010, pp. 1173-1181.)... 

The last session Waterborne Polymers included 8 presentations. There were discussed the next problems synthesis of smart nano-hydrogels, influence of adsorbed polymers on keratin surface properties in an aqueous environment, pH- and temperature-sensitive microgels for stimuli controlled emulsion stabilisation, industrial application of mini-emulsion polymerization in the coating field, PLURONIC block copolymers in balanced microemulsions. 

Senff H, Richtering W (1999) Temperature sensitive microgel suspensions colloidal phase behavior and rheology of soft spheres. J Chem Phys 111 1705-1711... 

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