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

The tert-butoxy radical-facilitated grafting of methyl methacrylate (MMA) o nto commercial polypropylene (PP) pellets and fiber was investigated in het erogeneous conditions similar to practical systems. Free-radical grafting o f several other monomers onto PP fiber was also investigated. Also, prelimi nary data from the grafting of MMA onto poly(ethylene terephthalate) pellet s is presented. The PP-graft-PMMA residues were detected by solid-state C-1 3-NMR and photoacoustic IR spectroscopy. There was a good correlation betwe en the degree of grafting (DG) determined from these spectroscopic techniqu es and the results from gravimetric methods. A maximum grafting efficiency of over 50% was found, whereas DG (20%) remained constant at various PP pel let, initiator, and monomer concentrations. However, at relatively low PP f iber concentrations, the DG was 27%; the increase was most likely due to th e greater surface area of the fiber. There was also a reduction in DG (14%) at relatively low initiator concentrations. The reaction conditions were a ltered to favor grafting by the addition of more polymer substrate. When th e ratio of tert-butoxy radicals to PP was decreased, more of the substrate remained unmodified, and empirical calculations showed the formation of gra fts with up to 40 monomer units. At high initiator concentrations, calculat ions showed that the graft residues were 1-2 units long. Therefore, variati on of the polymer, initiator, and monomer concentrations was shown to have a significant effect on grafting. (C) 2002 John Wiley & Sons, Inc. J Appl P olym Sci 83: 898-915, 2002.