The hydrolysis mechanism of bis(2,4-di-tert-butyl)pentaerythritol diphosphite (Alkanox P24): An atmospheric pressure photoionisation mass spectrometric study M. Papanastasiou a , A.W. McMahon b , N.S. Allen a, * , A.M. Doyle a , B.J. Johnson c , K. Keck-Antoine c a Faculty of Science and Engineering, Manchester Metropolitan University, Department of Chemistry and Materials, Center for Materials Science, Chester Street, Manchester M1 5GD, UK b University of Manchester, Molecular Imaging Center, 27 Palatine Road, M20 3LJ, UK c Chemtura, Toekomstlaan 13, B-2200 Herentals, Belgium Received 9 March 2006; accepted 23 April 2006 Available online 13 June 2006 Abstract Alkanox P24 is a commercial phosphite antioxidant, well known in the literature for its excellent processing stability. As in the case of many processing phosphites, however, Alkanox P24 might undergo hydrolysis when exposed to small amounts of water. A number of products pro- posed recently in the hydrolytic pathway of the phosphite [Ortuoste N, Allen NS, Papanastasiou M, McMahon A, Edge M, Johnson B, et al. Polym Degrad Stab; 2006;91:195e211] are investigated in this study by atmospheric pressure ionisation-mass spectrometry (API-MS). The ap- plicability of atmospheric pressure photoionisation (APPI) and atmospheric pressure chemical ionisation (APCI) ion sources is tested and the ion formation characteristics of Alkanox P24 are compared in both sources. In positive ion mode, ionisation of the parent phosphite occurred by protonation. In negative ion mode no pseudo-molecular ion peak was detected and the deprotonated species were more dominant in APPI. This source was employed further for the investigation of the hydrolysis products, since it exhibited lower limits of detection. High performance liquid chromatography (HPLC) with single ion monitoring (SIM) detection was used for the separation of the species formed. Hydrolysis of the phosphite proceeded via the scission of the two PeO phenol bonds exclusively to give 2,4-di-tert-butyl phenol quantitatively as a final product. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Polymer additives; Hydrolysis; APPI; APCI; HPLCeMS 1. Introduction Additives play a crucial role in the polymer industry over- coming processing problems, performance limitations and sta- bilisation issues. Traditional blends contain a combination of primary hindered phenols with secondary organophosphite an- tioxidants, providing excellent performance for the prevention of thermo-oxidative degradation of the polymer [2]. Bis(2,4- di-tert-butyl)pentaerythritol diphosphite (Alkanox P24) is an important member of this category, employed mostly in poly- olefin protection. The phosphitic and the partially hindered phenolic moieties that it contains are considered responsible for the high protective efficiency of the phosphite [3,4]. It is well known that some phosphorous-containing antiox- idants are particularly sensitive to hydrolysis leading to re- duced performance and to the formation of acidic species [5]. The influence of hydrolysis upon the processing stabilisa- tion performance of Alkanox P24 was evaluated and contrary to the general perception, hydrolysis led to the enhancement of this performance. Species thought to be formed during partial hydrolysis were found to be active processing stabilisers, of- fering better antioxidant activity than the parent phosphite * Corresponding author. Tel.: þ44 161 247 1453; fax: þ44 161 247 6357. E-mail address: n.s.allen@mmu.ac.uk (N.S. Allen). 0141-3910/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2006.04.023 Polymer Degradation and Stability 91 (2006) 2675e2682 www.elsevier.com/locate/polydegstab