Radiation grafting of styrene to polypropylene

Consistent with the preceeding acid work, when TMPTA is added to the monomer solutions containing either lithium salt or urea, synergistic effects are observed for the radiation grafting of styrene to polypropylene (Table IV). Again the maximum increase in yield occurs in the monomer solution corresponding to the Trommsdorff peak. 

Effect of Solvents on Radiation Grafting of Styrene to Polypropylene ... 

Fig. 2. Effect of miscellaneous solvents on radiation grafting of styrene to polypropylene film at dose rate of 4.0 x 10 rad/hr to total dose of 0.2 X 10 rad except dioxan (4.5 x 10 and 0.3 X 10 ).

Fig. 1. Acid effect in radiation grafting of styrene to polypropylene film (isotactic, doubly oriented, 0.06 mm) in methanol and ethanol at dose rate of 4.5 x 10" rad/hr to...

J.L. Garnett and N.T. Yen, Acid Effects in the radiation-induced grafting of styrene to polypropylene, Aust.J.Chem. 32 585 (1979). 

A theory for this acid effect has been developed essentially from the wool and cellulose work (3,4). Recently, in a brief communication, we reported analogous acid enhancement effects in the radiation grafting of monomers such as styrene in methanol to nonpolar synthetic backbone polymers like polypropylene and polyethylene (5). In the present work, detailed studies of this acid enhancement effect are discussed for the radiation grafting of styrene in various solvents to polyethylene. The results are fundamentally important since most of the experiments reported here have been performed in solvents such as the low molecular weight alcohols which, unlike cellulose and wool systems, do not swell polyethylene. 

Table 1. Effect of Sulfuric Acid (0.02 M) on Radiation Grafting of Styrene in Low Molecular Weight Alcohols to Polypropylene Film ...

The inclusion of divinylbenzene (DVB) enhances the radiation grafting of styrene in methanol to polypropylene (Figure 7) especially at concentrations above 30% monomer where there is generally a 100% increase in yield. Compared with acid and neutral solutions, the Trommsdorff peak in the DVB solution has moved slightly to higher monomer concentration for polypropylene grafting. The acid enhancement is greater than the DVB effect at monomer concentrations lower than 30%, but the reverse holds above this styrene level with polypropylene. 

Although considerable work has been reported using preirradiation grafting, the present treatment will be confined to the mutual or simultaneous procedure since by this latter technique, much lower doses are needed to accomplish a particular percentage graft The simultaneous method is also amenable to the use of additives to accelerate copolymerization. The additives to be discussed in this paper include solvent, mineral acid and polyfunctional monomers for the grafting of styrene monomer to polyethylene and polypropylene films in the presence of gamma radiation ... 

In preliminary work (19), divinylbenzene (DVB) has been reported to be a useful additive for enhancing the above grafting reactions. These early data (19) indicate that there are possible common mechanistic pathways between the acid effect and the DVB process. More detailed DVB studies are discussed in this paper for enhancing the radiation grafting yields of styrene in methanol to films of polyethylene and polypropylene. The work has been extended to include the use of other polyfunctional monomers such as tri-methylol propane triacrylate (TMPTA) as additives. The possibility of being able to use these additives for copolymerisation of monomers to naturally occurring trunk polymers such as cellulose will also be considered. 

The optimum in the copolymerisation process occurs at 50% monomer concentration with both additives. The behaviour of sulfuric acid in these reactions is representative of the most reactive of the mineral acids (12). A comparison of TMPTA with H SO (0.2 M) also indicates that similar trends in enhancement in radiation grafting to polyethylene film are observed with both additives (Table III). Again, when polypropylene film is used as backbone polymer (Table IV), acid and DVB show similar increases in grafting yield with styrene in methanol, however in this system, it is interesting to note that the concentration of monomer at the position of the Trommsdorff peak does not vary for neutral and acidified grafting solutions but changes from 30% to 35% when DVB is additive. 

Styrene in methanol radiation grafted to polypropylene film (0.06 mm) at 4.1x10 rad/hr to dose of 2.4x10 rad in air. 

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