Trommsdorff peak

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. 

In like manner, inclusion of mineral acid in the photo-sensitised grafting of styrene in methanol to cellulose enhances the polymerisation yields significantly (Figure 2). The results obtained with phosphoric and sulfuric acids were consistent with earlier data (13,14). Dioxan is also a useful solvent for these reactions when uranyl ion is used as sensitiser. However dioxan is not as efficient as methanol for the grafting reaction. The grafting in dioxan exhibits a Trommsdorff peak at 60% monomer concentration. The results in Figure 2 also show that the unsensitised process does occur in dioxan as in other solvents, but... 

When the total radiation dose is increased to 1.0 X 106 rads (Table XI) at the same dose rate as previously, significant gel peaks appear at 20%-40% monomer concentrations in all nonacidified alcohol solutions. Addition of acid leads to an enhancement in these Trommsdorff peaks for the first three alcohols studied. When dimethyl formamide is used as solvent at 2.0 X 105 rads, a Trommsdorff peak is observed at 60% styrene... 

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. 

In the UV Initiated grafting reactions, the addition of DVB and TMPTA accelerate the process similarly to that observed In the gamma ray system. However the magnitude of the enhancement with the polyfunctlonal monomers with UV Is much higher than with acid. The presence of these monomers also causes a shift In the Trommsdorff peak from 40 to 50% styrene concentration. The medianlsm of the DVB and TMPTA enhancement In grafting with UV appears to be the same as for the gamma system. 

This viscosity increase would then lead to an enhanced Trommsdorff peak as observed in the presence of acid. In reverse, the acid effect in grafting may well be used to substantiate the proposed viscosity explanation for the mechanism of the Trommsdorff effect in general polymerization reactions. 

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. 

When polyethylene is used as trunk polymer (Figure 7), the inclusion of DVB in the styrene-methanol grafting solution leads to a significant enhancement in copolymerisation, especially at the Trommsdorff peak. The effect of acid and DVB are similar with polyethylene grafting except above 60% monomer where the DVB enhancement is significantly higher. 

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