Graft copolymerization studies. III. Methyl methacrylate onto polypropylene and polyethylene terephthalate

The tert-butoxy radical-facilitated grafting of methyl methacrylate (MMA) onto commercial polypropylene (PP) pellets and fiber was investigated in heterogeneous conditions similar to practical systems. Free-radical grafting of several other monomers onto PP fiber was also investigated. Also, preliminary data from the grafting of MMA onto poly(ethylene terephthalate) pellets is presented. The PP-graft-PMMA residues were detected by solid-state C-13-NMR and photoacoustic IR spectroscopy. There was a good correlation between the degree of grafting (DG) determined from these spectroscopic techniques and the results from gravimetric methods. A maximum grafting efficiency of over 50% was found, whereas DG (20%) remained constant at various PP pellet, initiator, and monomer concentrations. However, at relatively low PP fiber concentrations, the DG was 27%; the increase was most likely due to the greater surface area of the fiber. There was also a reduction in DG (14%) at relatively low initiator concentrations. The reaction conditions were altered to favor grafting by the addition of more polymer substrate. When the ratio of tert-butoxy radicals to PP was decreased, more of the substrate remained unmodified, and empirical calculations showed the formation of grafts with up to 40 monomer units. At high initiator concentrations, calculations showed that the graft residues were 1-2 units long. Therefore, variation of the polymer, initiator, and monomer concentrations was shown to have a significant effect on grafting. (C) 2002 John Wiley & Sons, Inc. J Appl Polym Sci 83: 898-915, 2002.