Biomaterials 23 (2002) 4855–4862 Synthesis, surface properties and performance of thiosulphate- substituted plasticized poly(vinyl chloride) S. Lakshmi 1 , A. Jayakrishnan* Polymer Chemistry Division, Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences & Technology, Satelmond Palace Campus, Trivandrum 695012, India Received 2 April 2002; accepted 10 June 2002 Abstract Plasticized poly(vinyl chloride) (PVC) was surface modiﬁed by nucleophilic substitution of the chlorine atoms of PVC by thiosulphate in aqueous media in the presence of a phase-transfer catalyst. The properties of the modiﬁed surface were evaluated by contact angle measurements, attenuated total reﬂection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. Migration of the plasticizer di-(2-ethylhexyl) phthalate from control as well as modiﬁed PVC was examined in hexane, in cottonseed oil and in poly(ethylene glycol)-400 (PEG-400). While the modiﬁed PVC was found to be highly migration resistant in hexane, cottonseed oil and PEG-400 extracted the plasticizer. The modiﬁed PVC was found to cause haemolysis and was cytotoxic. A possible explanation for the difference in performance of the modiﬁed material in different extraction media and its toxicity is presented from a mechanistic view of the substitution process. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Poly(vinyl chloride); Plasticizer migration; Di-(2-ethylhexyl) phthalate; Thiosulphate; Surface modiﬁcation 1. Introduction Poly(vinyl chloride) (PVC) is the most extensively used polymeric material in medical and related applica- tions [1]. PVC is a rigid polymer and additives such as plasticizers are added to make it soft and ﬂexible. Flexible PVC contains up to 40% or more by weight of the plasticizer, usually di-(2-ethylhexyl) phthalate (DEHP) [2]. As the plasticizers are not held onto the base polymer by covalent linkages, they tend to migrate into surrounding medium. The toxicity of phthalate esters migrating into physiological media such as blood, serum, plasma, saliva and intravenous infusion ﬂuids etc., from PVC- based medical devices, into foods from PVC-based ﬁlms and wrappings and direct ingestion into children from PVC-based toys and tethers has been of great concern over many years [3–13]. Babies may ingest up to 6 mg of DEHP/day, sucking on plastic toys; but it is likely that a similar or higher consumption of this substance could be reached sucking on paciﬁers, tethers or plastic bottles or by skin contact with clothing or playpens [12,13]. In November 1999, the European Union Commission proposed an emergency and permanent ban of phtha- lates in toys and articles for children less than 3 yr of age. A very exhaustive and thorough review on the toxicity of DEHP has recently been published by Latini [14]. Various attempts have been made to prevent the migration of plasticizer from PVC based devices. They include coating PVC with various polymers like acrylates and urethanes, crosslinking PVC during processing using peroxides or by radiation, grafting hydrophilic monomers onto the surface, plasma treat- ment, substitution of chlorine on PVC with dialkyl dithiocarbamate followed by crosslinking and azidation of PVC followed by photocrosslinking [15–21]. In a recent communication [22], we showed that plasticized PVC could be made completely migration resistant without signiﬁcantly compromising its physical and mechanical properties by treating it with sodium sulphide in the presence of a phase-transfer catalyst *Corresponding author. Tel.: +91-471-340801; fax: +91-471- 341814. E-mail address: dr jkrishnan@sify.com (A. Jayakrishnan). 1 Present address: Department of Chemical Engineering, CAT Building, Room # 381, Drexel University, Philadelphia, PA 19104, USA. 0142-9612/02/$-see front matterr 2002 Elsevier Science Ltd. All rights reserved. PII:S0142-9612(02)00243-0