Effect of ethylene glycol dimethacrylate derivatives on photografting of methacrylic acid on low-density polyethylene

Abstract

Abstract Photografting of methacrylic acid (MAA) on low-density polyethylene (PE) film (thickness=30 μm), on which xanthone photoinitiator was coated earlier, was investigated at 60°C in the presence of ethylene glycol dimethacrylate derivatives (EGDMA) with different numbers of ethylene glycol unit between two double bonds in the molecule, such as di-, tetra- and nona-ethylene glycol dimethacrylates (2EG, 4EG and 9EG, respectively). Addition of the EGDMA (0.3–3 mol% of MAA used) to the grafting system largely accelerated the photografting and the magnitude of the enhancement decreased in the order of 9EG>4EG>2EG. EGDMA component was incorporated into MAA-grafted PE films and the content decreased in the order of 2EG>4EG>9EG. MAA-grafted chains of the grafted PE films (sample with EGDMA) prepared by photografting in the presence of EGDMA tended to appear at the film surface compared to those of the grafted films (sample without EGDMA) prepared in the system without EGDMA, which was measured by electron probe microanalysis and attenuated total reflection infrared spectroscopy. The MAA-grafted PE films exhibited a pH-responsive character, which was evaluated by measuring a dimensional change of the grafted films. The grafted films shrank in acidic media, but swelled in alkaline media. The sample with EGDMA showed a larger pH-responsive character than the sample without EGDMA though there was no large difference in the character among EGDMA. The phenomenon was discussed in terms of the MAA-grafted chains with a branched structure, which was suggested by differential scanning calorimetry of the grafted films.