Radiation-grafting of 2-hydroxyethylmethacrylate and oligo (ethylene glycol) methyl ether methacrylate onto polypropylene films by one step method
Highlights
► PP was grafted with a hydrogel layer applying the γ-ray pre-irradiation method. ► Effects of radiation dose, time, temperature and monomers concentration were evaluated. ► Grafted layer increases the hydrophilicity of PP films. ► HEMA and OEGMA grafted onto PP may be of interest for biomedical applications.
Introduction
Radiation grafting is a suitable technique for surface modification of polymeric materials since it allows introducing active functional groups on the polymer backbone (Nurkeeva et al., 2003, Meléndez-Ortiz et al., 2009, Contreras-Garcia et al., 2008, Ramírez-Fuentes et al., 2007, Alvarez-Lorenzo et al., 2010). This method is applicable for many substrates and monomers combinations and, unlike chemically initiated grafting; it does not require initiators (Vahdat et al., 2007). There are several methods of radiation grafting: (i) the direct (or mutual) grafting method in which the polymeric material is irradiated in contact with a monomer, homopolymerization being a collateral effect; (ii) the pre-irradiation method, which involves the irradiation of the polymer matrix in the absence of air and then the grafting is initiated by macroradicals trapped in the irradiated polymer; radiation dose is usually larger than in the direct method and polymer degradation may occur; and (iii) the pre-irradiation oxidative grafting method that consists in the pre-irradiation of the polymer in the presence of air or oxygen, so that the macroradicals formed are converted to peroxides and/or hydroperoxides, and when the irradiated polymer is heated in the presence of monomer the peroxides decompose to give the macroradicals (Bucio et al., 2010, Burillo and Bucio, 2009).
Currently there is an increasing interest in developing homogeneous polymer networks with controlled microstructure, particularly for highly demanding applications such as medical devices and controlled drug delivery systems (Kurjata et al., 2009). Combination of the mechanical properties of film supports with the recognized biocompatibility of hydrogels may open novel possibilities. The hydrogels obtained from the polymerization of 2-hydroxyethyl methacrylate (HEMA) are well-known in the biomedical and biotechnological fields due to their resemblance of biological tissues (Wichterle and Lim, 1960, Hoffman, 2006), hydrophilic character (Gregonis et al., 1978), and versatility to be copolymerized with functional monomers (Tomic et al., 2010). Generally, HEMA is thought to be a solvent-like monomer capable of homogenizing hydrophobic and hydrophilic phases (Sharrock and Grégoire, 2010). Oligo (ethylene glycol) methyl ether methacrylates, represent a very interesting family of monomers, since they are biocompatible and thermoresponsible materials and their solubility in aqueous solutions increases upon increasing the size of the ethylene glycol group (Driva et al., 2011). Poly (ethylene glycol) methyl ether methacrylate (PEGMA)-modified polymeric films could potentially be used for biomedical applications (Fournier et al., 2007, Luo et al., 2002). The aim of this work was to evaluate the possibilities of grafting of HEMA and OEGMA onto polypropylene (PP) films using a gamma-ray pre-irradiation method. PP is widely applied as component of medical devices such as catheters, artificial blood vessels, and equipment for extracorporeal circulation (Hernández-Martínez and Bucio, 2009). However, its hydrophobic surface prompts the unspecific adsorption of proteins and microorganisms (Nava-Ortiz et al., 2010, Nava-Ortiz et al., 2009a, Nava-Ortiz et al., 2009b). Hydrogel grafting is intended to enhance the hydrophilicity of the PP surface. The grafted films were obtained at various radiation conditions and characterized by FTIR-ATR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), water contact angle and swelling measurements.
Section snippets
Materials
Polypropylene (PP) films from Goodfellow England, 1 mm thickness and 1 cm×5 cm in size were washed in methanol for 2 h and then dried in vacuum to constant weight. Oligo (ethylene glycol) methyl ether methacrylate (OEGMA) and 2-hydroxyethylmethacrylate (HEMA, 97%) were from Aldrich Chemical Co., USA. HEMA was purified by vacuum distillation before use. Toluene and methanol from Baker were used as-received.
Grafting
PP films were exposed to 60Co γ-source (Gamma beam 651 PT, MDS Nordion) in the presence of
Incidence of reaction variables on the grafting yield
Radiation grafting of some methacrylic monomers, including HEMA and OEGMA, is accompanied by essential homopolymerization of the monomer and the oligomer, respectively. Gamma beam irradiation of PP under air produces latent initiating species as peroxides and hydroperoxides in unordered domains and, to a lower extent, trapped free radicals in crystalline regions (Scheme 1). The efficiency of the grafting polymerization (Yg) was assessed by gravimetry, after extensive washing and drying of
Conclusions
A new graft copolymer of PP-g-OEGMA/HEMA has been prepared by applying gamma-ray pre-irradiation method. The grafting percentage can be tuned through adequate combinations of radiation dose, monomers proportion and total concentration, reaction temperature and reaction time. In the grafting onto peroxidized polymers, the rate of initiation is determined by the radiation dose and the grafting temperature; these two parameters were well established in this paper. The maximum grafting obtained was
Acknowledgements
The authors thank to S. Castillo-Rojas, F. García, B. Leal, and A. Ramírez from ICN-UNAM for technical assistance. This work was supported by DGAPA-UNAM Grant IN202311, Mexico; and by MICINN and FEDER (SAF2011-22771), and the Xunta de Galicia (PGIDT10CSA203013PR), Spain.
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