Radiation Physics and Chemistry 75 (2006) 1060–1068 Post-irradiation crosslinking of partially cured unsaturated polyester resin Tanja Jurkin, Irina Pucic´ Ã RuXer Bosˇkovic´Institute, POB 180, Zagreb, Croatia Received 4 August 2005; accepted 2 April 2006 Abstract The post-irradiation crosslinking of unsaturated polyester (UP) resin samples irradiated to different doses was monitored during the 15-days period. The post-reaction sensitivity of three experimental techniques was evaluated. Significant changes were detected by extraction analysis that also included determination of the free styrene content. The most substantial changes were detected by differential scanning calorimetry, even up to 5 days after the irradiation. The sensitivity and reproducibility of FTIR was the lowest. The first two techniques detected the influence of particular reaction periods, at which the radiation crosslinking was terminated, on the post-reaction. r 2006 Elsevier Ltd. All rights reserved. Keywords: Extraction analysis; FTIR spectroscopy; Differential scanning calorimetry; Microgel; Gel effect; Vitrification 1. Introduction Although more than 40 years ago Chapiro (1962) described post-irradiation polymerization of solid sys- tems, not much attention is being paid to it in recent investigations of radiation reactions of polymers. Ivanov (1992) defined post-irradiation reaction as continuation of polymerization after the irradiation is terminated due to free radicals formed under the irradiation being trapped and stabilized in macromolecules or in the network, but post-irradiation degradation also occurs (Deng et al., 1998). The post-reaction course largely depends on the polymer under consideration and for some polymers no post-irradiation changes were de- tected, as in case of PVAc (Ivanov, 1992), or they vary depending on conditions of sample storage. The post- effects can last up to a year or more (Ali and Legocka, 2005) and significantly affect overall radiation reaction conversion. Consequently, it is very important to evaluate this phenomenon for a particular polymer. Almost 30% of recent articles on post-irradiation effects deal with UHMWPE because of its significance for artificial joint production and a need to improve its wear properties by radiation processing while avoiding its degradation that has substantial medical implications (Sugano et al., 2004; Oral et al., 2004). It should be mentioned that post-polymerization is a base for some types of radiation grafting that are gaining importance in production of polymer-coated nanoparticles (Tani- guchi et al., 2005; Ueda et al., 2005). Obviously, determination of the post-irradiation behavior should be a part of any study of all types of radiation-initiated reaction concerning polymers. The unsaturated polyester (UP) resins are most widely used thermosetting resins and are being increasingly applied for various purposes because of their balanced mechanical and chemical characteristics and a low cost (Aziz et al., 2005). The UP resins are being used as the polymer matrix for composites and, recently, ARTICLE IN PRESS www.elsevier.com/locate/radphyschem 0969-806X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2006.04.001 Ã Corresponding author. Tel./fax: +385 1 45 61 166. E-mail address: pucic@rudjer.irb.hr (I. Pucic´).