R ESEARCH ARTICLE doi: 10.2306/scienceasia1513-1874.2014.40.224 ScienceAsia 40 (2014): 224–231 Preparation of stable polymeric grafted layers on poly(ethylene terephthalate) by thermal annealing Peerasak Paoprasert a,* , Warisara Boonthong a , Chanatip Kookarinrat a , Nuanphun Chantarasiri b a Department of Chemistry, Faculty of Science and Technology, Thammasat University, Pathumthani 12121 Thailand b Supramolecular Chemistry Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330 Thailand * Corresponding author, e-mail: peerasak@tu.ac.th Received 29 Jan 2014 Accepted 11 May 2014 ABSTRACT: This work presents a simple and versatile grafting method to prepare stable polymer layers on poly(ethylene terephthalate) (PET). Poly(styrene-co-2-hydroxyethyl methacrylate) was synthesized by free radical polymerization. The copolymer was grafted onto poly(ethylene terephthalate) via the hydroxyl groups upon thermal annealing. The percentage of copolymer grafting was studied as a function of copolymer composition, PET surface treatment, annealing time, and annealing temperature. The grafted polymer layer on PET remained stable when immersed in an organic solvent whereas the non-grafted polymer layers were completely desorbed within two weeks. In addition, poly(4-vinylpyridine-co-2- hydroxyethyl methacrylate) was grafted onto PET to test the versatility of this grafting method. Control experiments were carried out to demonstrate that the grafting occurs through the available hydroxyl groups on the polymers and the surfaces. Based on these results, this grafting method offers a simple and versatile strategy to prepare stable polymeric layers on polymeric surfaces, and therefore, expands the tool box for functionalizing polymer surfaces. KEYWORDS: coatings, adhesion, polymer grafting, hydroxyl linker INTRODUCTION The modification of polymeric substrates by grafting is an important route to modify a polymer surface properties and to introduce new functions, for exam- ple, biocompatibility 1 , adhesion 2 , friction 3 , lubrica- tion 4 , hydrophobicity 5 , or hydrophilicity 6 , to the sub- strates. There are two main approaches to graft poly- mers onto solid surfaces: grafting-from and grafting- to 7, 8 . In the grafting-from method, the monomers react with a surface activated by high energy irradi- ation or a chemical initiator forming polymer chains tethered to the surface. In the grafting-to approach, the pre-synthesized polymer chains are anchored onto the solid surface through linker groups. The grafting- from method often yields high-density polymer layers, but has poor control over polymer molecular weight and distribution. In addition, it uses a large amount of starting materials, including the monomer and initiator (in the case of chemical grafting). Since the samples must be totally immersed in a solution, the grafting- from method produces abundant chemical waste and a relatively small amounts of polymers grafted to the surface. In contrast, in the grafting-to method, the polymer is pre-synthesized so that the desired molecular weight and distribution can be obtained prior to grafting. Less chemical waste is generated as a thin layer of polymer can be directly transferred to the substrate before the grafting step. The linker groups however must be installed in the polymer chains and therefore the proper linkers must be chosen and the polymerization conditions must be compatible. There are several linker groups for grafting or- ganic materials onto inorganic substrates. For exam- ple, silanes 9 , carboxylic acids 10 , phosphonic acids 11 , and catechols 12 are linkers for oxide surfaces whereas thiols are linkers for gold 13 . However, unlike the in- organic substrates, the polymeric substrates are more difficult to graft because most commodity polymers are inert or lack active groups such as surface hy- droxyls or metal atoms, to react with those linkers. There are only a few reports on grafting polymers on polymeric substrates, for example, fluorinated silane grafted poly(vinylidene fluoride) 14 , hydrophilic polymer-coated polydimethylsiloxane through silane linker 15 , and hepamine-coated polyurethane through catechol linker 16 . Grafting such polymers is difficult as the synthesis of these polymers requires several steps and the grafted polymeric layers may be unsta- ble. There is a need therefore to develop new grafting methods for the preparation of stable polymeric layers on polymer surfaces. www.scienceasia.org