Microgel

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Microgels are intramolecularly cross-linked macromolecules with colloidal dimensions, where it is necessary to control the growth of the cross- linked molecules during synthesis .

Microgels made from various materials have recently become increasingly important, for example as drug delivery systems, for enzyme and cell immobilization, as actuators in microvalves and as temperature-sensitive catalyst matrix . They are referred to in the literature as microspheres, microparticels, microlatex and microglobules.

properties

As early as 1986, a synthetic route and the characterization of a temperature-sensitive aqueous microgel, which was synthesized on the basis of NiPAM, was described.

A polymer is called sensitive if it reacts to a change in its environment with a change in its properties. Poly-N-isopropyl acrylamide changes its solubility behavior in aqueous solution when the temperature is increased above 32 ° C.

When the temperature is increased above the LCST, the microgel collapses

If the phase transition temperature of 32 ° C. is exceeded, the poly-N-isopropyl acrylamide becomes insoluble in water and precipitates out of the solution. This behavior is called Lower Critical Solution Temperature (LCST) and is not only found in linear polymers, but also in microgels, which consist of the corresponding monomers (NiPAM). Above the LCST, the microgels collapse and release the trapped solvent into the environment. Below the LCST, the microgels are penetrated by the solvent and thus swollen. Depending on the degree of crosslinking and the solvent through which a microgel is penetrated, the swelling of the microgel varies.

To synthesize pH-sensitive microgels, polyacrylic acid copolymers or poly-2-vinylpyridine (P2VP) are polymerized. Temperature-sensitive microgels are obtained when poly- (N-vinylcaprolactam), poly-N-isopropyl acrylamide (PNiPAM) or similar polyamides are used in the synthesis.

Individual evidence

  1. ↑ a b c d Seifert, D. Dissertation Synthesis and characterization of sensitive crosslinkable block copolymers using RAFT; Dresden, 2004.
  2. ↑ Ishizu, K., J. Polym. Sci. Lett ED C 26 1988, 281.
  3. ↑ Bauer, DR; Briggs, LM; Dickie, RA, Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 686.
  4. ↑ Holtzscher, C .; Durand, JP; Candau, F., Coll. Polym. Sci. 1987, 265, 1067.
  5. ↑ Karyakina, MI; Mogilevich, MM; Maiorova, NV; Udalova, AV, Vysokomol soedin A17 1975, 466.
  6. ↑ a b Pelton, R., Temperature-sensitive aqueous microgle. Advances in Colloid and Interface Science 2000, 85, 1.
  7. ↑ Heskins, M .; Guillet, JE, J. Macromol. Sci. Chem. A2 1968, 8, 1441.
  8. ^ Schild, HG, Prog. Polym. Sci. 1992, 17, 163.