EFFECT OF ETHYLENE-GLYCOL DIMETHACRYLATE DERIVATIVES ON PHOTOGRAFTINGOF METHACRYLIC-ACID ON LOW-DENSITY POLYETHYLENE

Photografting of methacrylic acid (MAA) on low-density polyethylene (P E) film (thickness = 30 mu m), on which xanthone photoinitiator was co ated earlier, was investigated at 60 degrees C in the presence of ethy lene 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 magn itude of the enhancement decreased in the order of 9EG > 4EG > 2EG. EG DMA component was incorporated into MAA-grafted PE films and the conte nt decreased in-the order of 2EG > 4EG > 9EG. MAA-grafted chains of th e grafted PE films (sample with EGDMA) prepared by photografting in:th e presence:df EGDMA tended to appear at the film surface compared to t hose of the grafted films (sample without EGDMA) prepared in the syste m without EGDMA, which was measured by electron probe microanalysis an d attenuated total reflection infrared spectroscopy. The MAA-grafted. PE films exhibited a pH-responsive character, which was evaluated by m easuring 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 pa-responsive character than the sample without EGDMA though there was no large difference in the character among EGD MA. The phenomenon was discussed in terms of the MAA-grafted chains wi th a branched structure, which was suggested by differential scanning calorimetry of the grafted films. (C) 1998 Elsevier Science Ltd; All r ights reserved.