Surface Modification of Ethylene-co-Acrylic Acid Copolymer Films: Addition of Amide Groups by Covalently Bonded Amino Acid Intermediates Ning Luo, 1 Michael J. Stewart, 1 Douglas E. Hirt, 1 Scott M. Husson, 1 Dwight W. Schwark 2 1 Department of Chemical Engineering and Center for Advanced Engineering Fibers and Films, Clemson University, Clemson, South Carolina 29634 2 Cryovac Division of Sealed Air Corporation, Duncan, South Carolina 29334 Received 24 March 2003; accepted 21 September 2003 ABSTRACT: Amide groups were anchored covalently on the surface of ethylene-co-acrylic acid (EAA) copolymer film by surface grafting of amino acid intermediates. The process consisted of four steps: conversion of carboxylic acid groups on the EAA surface to acid chloride groups, amino acid attachment, conversion of amino acid carboxyl groups to acid chloride groups, and amidation. All steps were carried out at room temperature. ATR-FTIR spectroscopy was used to characterize the film after each step and to measure the kinetics of amino acid attachment. Three amino acids were studied: 12-aminododecanoic acid (12-ADDA), 5-aminoph- thalic acid (5-APA), and l-aspartic acid (AA). The longer- chain 12-ADDA compound was selected for its chemical similarity to migratory fatty amides that are commonly used to alter the frictional behavior of polyolefin films. The 5-APA and AA compounds were selected because each has two carboxylic acid groups that can be converted to amide groups. After amidation, the modified EAA films were char- acterized by static water contact angle measurements and scanning probe microscopy. Results showed that the 12- ADDA reacted to the surface much faster than the 5-APA or AA. Several steps of aggressive rinsing confirmed that the 12-aminododecanamide was chemically anchored onto the EAA surface. As a result, both hydrophilicity and surface roughness were increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1688 –1694, 2004 Key words: amino acid; surface modification; ethylene-co- acrylic acid copolymer; amidation; ATR-FTIR INTRODUCTION As early as the late 1950s, a series of articles reported results on the grafting of amino acids on polysaccha- ride polymers (e.g., cellulose). 1–5 By altering the chem- istries used, amino acids or their derivatives can be attached to cellulose or other polymeric surfaces through reaction of either their amino or carboxyl functional group(s). Many applications that use sur- face-grafted amino acids exploit their abilities to selec- tively and efficiently recognize proteins and thereby resist or encourage surface adsorption of specific pro- teins. For example, amino acids bonded covalently to the surfaces of conventional polymeric membranes transform them into pseudobiospecific affinity mem- branes in the purification of a variety of proteins. 6 In this study, we examined a new application: the use of grafted amino acids as intermediates in a process to alter the frictional properties of polymeric films. The ways in which amino acids are grafted onto polymer surfaces are varied. For polyethylene mem- branes and films, amino acids can be bonded co- valently to the surface by direct Ar + irradiation 7 or by reacting with grafted polymer chains in a two-step process. In the latter method, poly(glycidyl methacry- late) is first grafted on polyethylene by electron-beam or -ray irradiation. Subsequently, amino acids are attached by sequential ring-opening reactions be- tween amine groups in the amino acids and epoxy groups on the grafted poly(glycidyl methacrylate). 8 –11 Polyacrylic acid has also been used as a grafted inter- mediate layer for subsequent attachment of amino acids on polyethylene membranes. 12 Here, the amine groups of the amino acid are coupled with the carbox- ylic acid groups of polyacrylic acid. Wu et al. 13 mod- ified the surface of poly(ethylene terephthalate) (PET) film with glycine by a method that involved UV graft- ing of polyacrylamide and sequential reactions. The glycine-grafted PET film was then reacted with oligo- peptides for applications in biomaterials. Amino acids have been attached covalently to the surface of poly- urethane by the reaction with sodium sulfonate 14 or hydroxyl 15 groups. Correspondence to: D. Hirt (hirtd@clemson.edu). Contract grant sponsor: Cryovac Division of Sealed Air Corporation. Contract grant sponsor: National Science Foundation; contract grant numbers: CTS-9983737 and EEC-9731680. Journal of Applied Polymer Science, Vol. 92, 1688 –1694 (2004) © 2004 Wiley Periodicals, Inc.