Transforming Plastic Surfaces with Electrophilic Backbones from Hydrophobic to Hydrophilic Samuel Kim, † Raffick A. R. Bowen, ‡ and Richard N. Zare* ,† † Department of Chemistry and ‡ Department of Pathology, Stanford University, Stanford, California 94305, United States * S Supporting Information ABSTRACT: We demonstrate a simple nonaqueous reaction scheme for transforming the surface of plastics from hydrophobic to hydrophilic. The chemical modification is achieved by base-catalyzed trans-esterification with polyols. It is permanent, does not release contaminants, and causes no optical or mechanical distortion of the plastic. We present contact angle measure- ments to show successful modification of several types of plastics including poly(ethylene terephthalate) (PET) and polycarbonate (PC). Its applicability to blood analysis is explored using chemically modified PET blood collection tubes and found to be quite satisfactory. We expect this approach will reduce the cost of manufacturing plastic devices with optimized wettability and can be generalized to other types of plastic materials having an electrophilic linkage as its backbone. KEYWORDS: surface modification, glycolysis, PET, blood collection devices, wettability, contact angle 1. INTRODUCTION Plastics are made of organic polymers and have excellent properties, such as light weight, moldability, chemical and physical durability, and electrical and thermal insulation, in conjunction with low manufacturing cost. Consequently, plastics have found ubiquitous uses in modern life. Unlike glass, however, plastics have poor wettability. This characteristic can sometimes interfere with their use because the plastic easily adsorbs other hydrophobic molecules in contact with its hydrophobic surface. 1,2 Therefore, modification of a hydro- phobic polymeric surface into a hydrophilic one is frequently desired. Conventional approaches for converting hydrophobic plastic surfaces to hydrophilic include plasma treatment, 3-6 UV irradiation, 7,8 and graft polymerization. 9,10 The physical method of exposing surfaces to plasma and photons are widely used as a general, fast, and adjustable approach to modify various types of plastics. 11 The costs for vacuum environment and equipment, however, are higher than other methods. Moreover, in the case of poly(ethylene terephthalate) (PET), a widely used plastic, the plasma-treated surface has been reported to relapse to a certain degree of hydrophobicity over storage time presumably because of the rearrangement of introduced functional groups. 12-14 Grafting technology is also a method for introducing new properties to the surface of a polymeric structure, but surface activation necessary to initiate polymer- ization of monomers or coupling reactions is often facilitated by plasma or UV treatment, thereby demanding again infra- structure costs. Some manufacturers overcome problems associated with the hydrophobicity of the plastic surface by coating it with surfactants. However, this approach raises the concern that the surfactants may interfere with other uses. 15 More recently, surface modification of PET based on melt blending with polyethylene glycol (PEG) was reported where the addition of polystyrene promoted surface presentation of the more hydrophilic component of PEG. 16 However, mixing with a different type of plastic can alter bulk properties, which may limit the applicability of this approach. Additionally, PEGylation of the PET surface via an adhesive coating has been proposed and shown to be effective for preventing adsorption of biomolecules, 17 with emphasis on biocompatibility in the context of cell culture. We describe an alternative method for making the surface of plastic materials hydrophilic. It is based on trans-esterification of the polymer surface in contact with liquids containing multiple hydroxyl groups per molecule, such as ethylene glycol and glycerol, in the presence of a base to catalyze the reaction under nonaqueous conditions (Figure 1). Our scheme is effective with organic polymers whose backbones are made of electrophilic linkages. For example, PET is a polymer made of ethylene glycol and terephthalic acid units with ester bond linkages (Figure 1a). When ethylene glycol, as a reactant, is deprotonated by a strong base catalyst, it becomes a nucleophile that attacks the carbonyl carbon of PET in its backbone. The polymeric chain breaks and incorporates hydroxyl groups from the polyol. This reaction, also called glycolysis, has been explored extensively as a viable method for decomposing PET wastes for recycling purposes. 18-20 It also has been applied to PET fibers to enhance their wettability using inorganic base catalysts. 21,22 In contrast to the harsh reaction conditions used in these previous efforts for complete depolymerization or trans- formation, our scheme was optimized for a milder condition, especially below the glass transition temperature of PET (about Received: November 5, 2014 Accepted: January 7, 2015 Published: January 7, 2015 Research Article www.acsami.org © 2015 American Chemical Society 1925 DOI: 10.1021/am507606r ACS Appl. Mater. Interfaces 2015, 7, 1925-1931