Cross-linked polymer microspheres

The synthesis of cross-linked polymer microspheres by dispersion polymerization using liquid R134a as the continuous phase. 

Polymer Synthesis using Hydrofluorocarbon Solvents Synthesis of Cross-Linked Polymer Microspheres by Dispersion Polymerization in R134a... 

PVA must be cross-linked in order to be useful for a wide variety of applications. A hydrogel can be described as a hydrophilic, cross-linked polymer, which can sorbe a great amount of water by swelling, without being soluble in water. Other specific features of hydrogels are their soft elastic properties, and their good mechanical stability, independent of the shape (rods, membranes, microspheres, etc.). 

Albertsson and coworkers [240-244] carried out extensive research to develop polymers in which the polymer properties are altered for different applications. The predominant procedure is ring-opening polymerization which provides a way to achieve pure and well defined structures. They have utilized cyclic monomers such as lactones, anhydrides, carbonates, ether-lactones. The work involved the synthesis of monomers not commercially available, studies of polymerization to form homopolymers, random and block copolymers, development of cross-linked polymers and polymer blends, surface modification in some cases, and characterization of the materials formed. The characterization is carried out with respect to the chemical composition and both chemical and physical structures, the degradation behavior in vitro and in vivo, and in some cases the ability to release drug components from microspheres prepared from the polymers. 

Andrianov, A.K, L.G. Payne, K.B. Visscher, H.R. Allcock and R. Langer, Hydrolytic degradation of ionically cross-linked polyphosphazene microspheres,/OTtrnaf of Applied Polymer Science, 53 (1994) 1573-1578. At tursson, R, P. Edman and 1. Sjoholm, Biodegradable Microspheres. 1. Duration of action of dextranase entrapped in polvacrylstarch microparticles in vivo. The Journal of Pharmacology and Experimental Therapeutics, 231 (1984) 705—712. 

S.R. Jameela, A. Misra, and A. Jayakrishnan, Cross-linked chitosan microspheres as carriers for prolonged delivery of macromolecular drugs, / Biomater. ScL Polym. Ed., 6 (7), 621-632,1995. 

Thibault RJ, Hotchkiss PJ, Gray M, Rotello VM. Thermally reversible formation of microspheres through non-covalent polymer cross-linking. J Am Chem Soc 2003 125 11249-11252. 

Starting from monomers Monomers in bulk or in solution are irradiated. Polymerization takes place as the first stage of reaction. The polymer chains are then cross-linked. It is frequent practice to add bifunctional monomers to increase the efficiency of cross-linking. Typically, this procedure is used for synthesis of wall-to-wall hydrogels or microspheres. For biomedical use of the formed gels, all non-reacted monomers and residues have to be extracted. 

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