Atomic force microscopy study of the photografting of glycidyl methacrylate onto HDPE and the microstructure of the grafted chains Huiliang Wang a,b , Hugh R. Brown a, * a Engineering Faculty, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia b College of Chemistry, Beijing Normal University, Beijing 100875, China Received 27 June 2006; received in revised form 20 November 2006; accepted 25 November 2006 Available online 18 December 2006 Abstract This article presents an atomic force microscopy (AFM) study of the initial stage of the photografting of glycidyl methacrylate (GMA) onto high-density polyethylene (HDPE) surface and the microstructure of the grafted chains. The grafting was carried out in acetone, dichloro- methane and tetrahydrofuran (THF), as well as without solvent. Granular structures were found on the surface of the samples grafted in the solvents. The height of the granules increased linearly with their diameter. Each granule was thought to be a single grafted chain with a highly branched (or superbranched) microstructure. The grafting density on HDPE was quite small when the grafting was carried out in the solvents. The grafted chains were more branched when grafting was carried out in THF than when the grafting was carried out in acetone and dichloro- methane. The bulk (no solvent) grafting of GMA onto HDPE was much faster and more uniform than that carried out in the solvents. The thick- ness of the bulk grafted materials was a few nanometers after 30 s irradiation, and possibly, the grafting density was much higher and the grafted polymers were much less branched than those produced in solvent. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Atomic force microscopy (AFM); Grafting; High-density polyethylene (HDPE) 1. Introduction Photo-induced grafting has become a very popular tech- nique for the modification and functionalization of polymeric materials due to its significant advantages, such as low cost of operation, mild reaction conditions, easy and controllable introduction of graft chains without affecting the bulk poly- mer, and the long-term stability of the grafted chains [1]. The technique involves initiation of the polymerization of vinyl or acrylic monomers at reactive sites generated usually through abstraction of hydrogen atoms from polymer surfaces by the excited triplet state of photoinitiator [2]. However, a major problem of conventional photografting is the difficulty in the control and characterization of both the grafting density (number of grafting sites per surface area) and the microstructure of graft polymer, including chain length and branches, etc. In recent years, with the extensive research on controlled/living radical polymerization to precisely control the polymerization and the polymer structure [3], living radi- cal graft polymerization onto polymeric materials has been developed and has drawn a lot of attention. Nitroxide stabi- lized free radical graft polymerization [4], typical and reverse atom transfer radical graft polymerization (ATRP) [5] and reversible addition-fragmentation chain-transfer (RAFT) graft polymerization [6] are the most widely used techniques. Yang and Ra ˚nby [7] and Ma et al. [8] developed two sequential ultraviolet (UV)-induced living graft polymerization methods to modify polymeric materials. Ma’s method consists of two steps. In the first step, a surface initiator is formed on a sub- strate under UV irradiation in the presence of benzophenone (BP) solutions; in the second step, the monomers are grafted to the substrate by a living polymerization initiated by the surface photoinitiator. Therefore, grafting density and graft polymer chain length could be controlled independently since initiator formation and graft polymerization occur * Corresponding author. Tel.: þ61 2 42213820. E-mail address: hbrown@uow.edu.au (H.R. Brown). 0032-3861/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2006.11.052 Polymer 48 (2007) 477e487 www.elsevier.com/locate/polymer