A MALDI, TGA, TG/MS, and DEA study of the irradiation effects on PMMA S.R. Tatro, G.R. Baker, K. Bisht, J.P. Harmon * Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620-5250, USA Received 23 May 2002; received in revised form 30 September 2002; accepted 2 October 2002 Abstract Poly(methyl methacrylate) (PMMA) (M w ¼ 6.4 £ 10 3 , PD ¼ 1.06) was irradiated under vacuum. The constant dose rate was 1.66 £ 10 4 rad/min at doses between 10 and 100 Mrad using a cobalt-60 source. The samples were then analyzed by matrix assisted laser desorption/ionization (MALDI), hyphenated thermogravimetric/mass spectrometry (TG/MS), and dielectric analysis (DEA), all novel methods for the analysis of polymers damaged by radiation. Gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC) were also used for analysis. This study evidenced main chain scission, the removal of ester side groups, and the production of monomer as a result of ionizing radiation. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Matrix assisted laser desorption/ionization; Poly(methyl methacrylate); Radiation 1. Introduction This study focuses on the irradiation of highly syndio- tactic poly(methyl methacrylate) (PMMA), and uses several novel methods to study radiation damage. By choosing a polymer that has been studied extensively [1–13], the results from the current study using novel techniques can be viewed in correlation with results of previously published findings. It has been documented that when PMMA is exposed to both g and ultraviolet radiation, main chain scission is the dominant occurrence in both air and vacuum [2,5]. As a result of the scission of the main chain, the molecular weight decreases, which, in turn, causes a decrease in the glass transition temperature [5]. Products include monomer, hydrogen gas, carbon dioxide, carbon monoxide, methane, and propane. The ratios of hydrogen, carbon dioxide, carbon monoxide, and methane to one another are roughly equivalent to the ratios of the elements contained in an ester side group [2]. A relatively new technique, matrix assisted laser desorption/ionization (MALDI), was developed in the late 1980s. The use of this technique allowed polymer molecules to be ionized and desorbed without fragmenting the molecules [14,15]. Its use for the analysis of synthetic polymers has been recently reviewed by McEwen and Peacock [16]. MALDI provides the weight average molecular weight (M w ), the number average molecular weight (M n ), and the polydispersity (PD). The classic definitions of these terms are as follows [17,18] M w ¼ P N x M 2 x P N x M x ð1Þ and M n ¼ P N x M x P N x ð2Þ where M w is the weight average molecular weight, M n is the number average molecular weight, N x is the total number of molecules of length x, and M x is the molecular weight of a molecule corresponding to a degree of polymerization x. The ratio of molecular weights is used to represent the breadth of the molecular weight distribution PD ¼ M w M n ð3Þ where PD is the polydispersity. As research continued, studies demonstrated MALDI to be an optimum technique for polymers with a narrow molecular weight distribution while problems arise with 0032-3861/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(02)00727-9 Polymer 44 (2003) 167–176 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 1-813-974-3397; fax: þ1-813-974-1733. E-mail address: harmon@chuma1.cas.usf.edu (J.P. Harmon).