The use of radiation technique in the synthesis of polymeric nanogels P. Ulanski, J.M. Rosiak * Institute of Applied Radiation Chemistry, Technical University of Lodz, Faculty of Chemistry, Wroblewskiego 15, 93-590 Lodz, Poland Abstract Irradiation of dilute, deoxygenated aqueous solutions of hydrophilic polymers with high-dose pulses of fast electrons leads to the simultaneous formation of many radicals on each polymer chain. These radicals undergo mainly intra- molecular recombination. In this way internally crosslinked macromolecules ± nanogels ± are formed. Current data on poly(vinyl pyrrolidone) show that during this process the weight-average molecular weight remains almost constant, but there is a pronounced decrease in the radius of gyration of macromolecules, an eect expected for the formation of compact, internally crosslinked structures. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 61.25.H; 61.82.P; 82.30.C; 82.50.G Keywords: Polymer; Poly(vinyl pyrrolidone); Aqueous solution; EB-irradiation; Crosslinking; Microgel; Nanogel 1. Introduction Radiation technique has already become one of the standard tools for the formation and steril- ization of polymer hydrogels, i.e. insoluble, but water-swellable materials made of hydrophilic polymers. The procedures applied are usually based on the irradiation of monomer or polymer solutions with a dose sucient to obtain a ``wall- to-wall'' gel. In parallel with the synthesis of macroscopic hydrogels, there is a growing interest in the formation and properties of tiny gel spheres or particles (microgels and nanogels, the latter having sub-micron dimensions). Among the pos- sible uses of nanogels, the most important seem to be biomedical applications, such as drug- and vaccine-delivery systems, including tissue-speci®c drug targeting, enzyme immobilization and im- munoassay probes (e.g. Refs. [1±5]). Both classical polymer chemistry and radiation chemistry provide synthetic methods to obtain polymeric micro- and nanogels (e.g. Refs. [6±9], for examples of radiation-induced processes see Refs. [10±14]). These procedures are almost ex- clusively based on polymerization and thus they involve monomers as the basic substrates. Al- though these methods are eective and allow to control the size and composition of the micro- scopic polymer structures, there is often a question of the residual monomer in the ®nal product, a Nuclear Instruments and Methods in Physics Research B 151 (1999) 356±360 www.elsevier.nl/locate/nimb * Corresponding author. Tel.: +48-42-631-3196; fax: +48-42- 636-0246; e-mail: rosiakjm@mitr.p.lodz.pl 0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 0 8 5 - 3