International Journal of Mass Spectrometry 311 (2012) 31–39 Contents lists available at SciVerse ScienceDirect International Journal of Mass Spectrometry j our na l ho me page: www.elsevier.com/locate/ijms Fragmentation pathways of methacrylic homopolymers with labile trialkylsilyl ester side-groups—A mass spectrometric investigation of the RAFT process Laurence Charles a,∗ , Marlène Lejars b , André Margaillan b , Christine Bressy b a Aix-Marseille Université – CNRS, UMR 6264: Laboratoire Chimie Provence, Spectrométries Appliquées à la Chimie Structurale, F-13397 Marseille Cedex 20, France b Université du Sud Toulon Var, EA 4323: Laboratoire Matériaux Polymères Interfaces Environnement Marin (MAPIEM), F-83162 La Valette du Var Cedex, France a r t i c l e i n f o Article history: Received 27 October 2011 Received in revised form 25 November 2011 Accepted 26 November 2011 Available online 6 December 2011 Keywords: Synthetic polymer Poly(methacrylate) Dissociation rule Structural characterization RAFT process a b s t r a c t Fragmentation pathways of methacrylic polymers containing labile silyl ester pendant groups were characterized upon collisional activation of electrosprayed oligomer adducts. Dissociation of lithiated oligomers mainly generated low mass product ions containing the  end-group and arising from back- bone bond homolytic cleavages, as typically observed for poly(alkylmethacrylate)s. Combined with the sum of the end-group masses as determined from MS data, this main reaction allowed both end-groups to be validated. In contrast, loss of HCOOR (with R = triisopropylsilyl) or elimination of alkene species from alkylsilyl groups, such as reported from poly(butylmethacrylate), was not observed here, probably due to steric hindrance of the pendant moieties. Activation of ammonium oligomer adducts was found to provide highly complementary information, since they exhibited a similar behavior as compared to poly(methacrylic acid), with serial eliminations of a triisopropylsilanol neutral conducting to the deter- mination of the polymerization degree of the dissociating precursor ion. It should be noted however that this useful pathway was not always observed to efficiently compete with dissociation of reactive  end- groups. Based on these fragmentation rules, five poly(triisopropylsilyl methacrylate)s were identified in a sample obtained via reversible addition-fragmentation chain transfer (RAFT) polymerization using cyanoisopropyl dithiobenzoate as the chain transfer agent. Their structure could be rationalized with regards to RAFT processes: (i) dormant chains initiated by a cyanoisopropyl group and terminated by a dithiobenzoate group, as the main species; (ii) proton- and (iii) vinyl-terminated dead chains produced by disproportionation termination events; (iv) ,-cyanoisopropyl-terminated polymer chains arising from a combination termination between two macromolecular propagating radicals, and (v) dormant chains containing methacrylic acid monomer units within the chain. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Synthesis and design of polymer materials containing hydrolyt- ically labile bonds have been a subject of scientific and commercial interest over the past 40 years in marine antifouling applications [1]. Bioactive polymer materials are specifically formed by direct incorporation of bioactive agents into a seawater hydrolyzable polymer matrix. In this context, the initially water-insoluble poly- mer matrix is solubilized in water through hydrolysis of labile ester bonds. This polymer hydrolysis reaction leads to a mass loss of the material with time and this resulting erosion mech- anism contributes to the bioactive agent elution response. Use of trialkylsilyl (meth)acrylate based-polymers as potential deliv- ery systems has been rarely reported in the literature [2]. It is worth noting that trialkylsilyl ester groups are well known as ∗ Corresponding author. Tel.: +33 491 28 8678; fax: +33 491 28 2897. E-mail address: laurence.charles@univ-provence.fr (L. Charles). conventional protecting groups of carboxylic acid functions and are readily deprotected under basic and/or acidic hydrolysis reaction [3]. In addition, the reactivity of a silyl ester linkage was reported to be highly dependent upon the steric and electronic properties of the alkyl groups attached to the silicon atom [4]. In this work, reversible addition–fragmentation chain transfer (RAFT) polymerization was selected to synthesize triisopropylsilyl methacrylate-based poly- mers (poly(TIPSiMA)) with a well-defined chain architecture and a narrow molecular weight distribution. The RAFT process is based on the main principle that consists of the introduction of thio com- pound derivatives acting as chain-transfer agents (Supplementary Scheme S1). In this procedure, control is achieved through a rapid equilibration between a low concentration of active propagat- ing radicals (P n • ) and a predominant fraction of dormant species end-capped by a thiocarbonylthio group [5]. A too high concentra- tion of propagating radicals P n • affects the control of the polymer chain growth with the formation of dead polymer chains through combination and disproportionation termination reactions [6]. The preservation of thiocarbonylthio chain end functionality is 1387-3806/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ijms.2011.11.015