GRAFT-COPOLYMERS OF POLYPROPYLENE FILMS .1. RADIATION-INDUCED GRAFTING OF MIXED MONOMERS

Radiation graft copolymerization of comonomer mixtures of acrylic acid (AAc) and styrene (S) onto polypropylene (PP) films by the mutual met hod has been investigated. The effect of different factors that may af fect the grafting yield, such as inhibitor concentration (Mohr's salt) , solvent composition (MeOH and H2O), radiation dose and dose rate, wa s studied. It was found that Mohr's salt was very effective when the c ontent of AAc in the comonomer mixtures was low. However, the addition of 1 . 25 wt% of Mohr's salt reduced homopolymer formation and enhanc ed the grafting process. Graft copolymerization in the presence of a s olvent mixture composed of methanol and water was found to afford a hi gher grafting yield than in pure methanol, regardless of the compositi on of the comonomer mixture used. However, the highest degree of graft ing was obtained at a solvent composition of 20% H2O:80% MeOH and a co monomer mixture of 20% AAc:80% S. An attempt was made to determine eac h PAAc and PS fraction by different methods in the graft copolymer obt ained. Elemental analysis indicated that the PAAc fraction with respec t to PS in the graft copolymer decreased with increasing AAc ratio in the comonomer feed solution. The rough assessment of these fractions b y IR spectroscopy showed similar trends. The reactivity ratios of AAc and S monomers determined in the present graft copolymerization system were found to be 0 . 45 and 1 . 3, respectively.