Degradation on polyacrylamides. Part I. Linear polyacrylamide Marcus J. Caulfield, Xiaojuan Hao, Greg G. Qiao, David H. Solomon * Polymer Science Group, Department of Chemical Engineering, The University of Melbourne, Melbourne, Vic. 3010, Australia Received 14 June 2002; received in revised form 17 December 2002; accepted 19 December 2002 Abstract The stability of linear polyacrylamides (PAAM) under thermal and irradiation conditions were investigated. The study showed that PAAm is stable under fluorescent lights and does not release any detectable acrylamide (AAM) in hot aqueous solution at 95 8C. Hydrolysis of side- chain amide groups to acid groups was observed during the thermal aqueous degradation. Under UV irradiation, small levels of released AAm were observed; however they are generally below 50 parts per million repeat monomer units in the polymer. A drop in viscosity is also observed. This indicates that the acrylamide released is due to chain scission, not a unzipping of the polymer chain. Methods of purifying a linear PAAM are also discussed. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Polyacrylamide; Degradation; Hydrolysis 1. Introduction Polyacrylamides (PAAm) find wide use as water purification flocculants [1–4], as soil conditioning agents [5–8], as hydrogels [9] including contact lenses, and in many biomedical applications [10–13]. In particular, gels or membranes made from polyacrylamides have been exten- sively used in recent years for protein separations [14–17]. Polyacrylamide is generally, but not universally accepted as being non-toxic. However acrylamide monomer causes peripheral neuropathy. Thus the level of acrylamide monomer in commercial polymers has been an important issue particularly for applications where human contact is involved. For example, polyacrylamide used as a water purification agent has strict specifications on the amount of monomer that is allowed. Similarly, polyacrylamide membranes used in blood purification require no detectable monomer or techniques for removing residual monomer. Recently it has been suggested that an additional but vitally important concern is the possibility of degradation of commercial polyacrylamide formulations to acrylamide. Such reports have been challenged but the question remains as to whether or not polyacrylamide can release acrylamide monomer and if so the extent of such degradation processes. In this paper we report on the stability of a number of PAAms, prepared with different initiation systems, when heated, exposed to irradiation of fluorescent light (indoor laboratory condition), exposed to ultraviolet irradiation (outdoor condition), and kept at room temperature. We then use these results to rationalize the conflicting reports in the literature. 2. Experimental and results 2.1. Materials Electrophoresis-grade (. 98%) acrylamide was pur- chased from ICN Biomedicals Inc.; ammonium persulphate (APS) (. 98.8) was obtained from Sigma Chemical Co.; H 2 O 2 (AR grade, 30% w/v) was obtained from AJAX Chemicals; and N, N, N 0 , N 0 tetramethylethylenediamine (TEMED) (. 99.5%) from Aldrich. Bromine (AR grade) was obtained from FSE Pty Ltd. Saturated bromine water was made by shaking Milli Q water with bromine followed by standing the solution overnight at 4 8C. The aqueous phase was used. Sodium thiosulphate (. 99.5%) was purchased from AJAX Chemicals and 1M solution sodium thiosulphate was used. Spectrophotometric grade trifluoroacetic acid (TFAA, . 99%) was obtained from Aldrich Chemical Co. 0032-3861/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0032-3861(03)00003-X Polymer 44 (2003) 1331–1337 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ61-03-8344-8200; fax: þ 61-03-8344- 4153. E-mail address: davids@unimelb.edu.au (D.H. Solomon).