Chain-transfer coefficients (Cs) with twenty-six different solvents at 60° C for acrylonitrile (M) have been measured by catalyzed polymerization studies using azobisisobutyronitrile (I) as catalyst ([l]/[M] = 6.1 x 10 -4 mol/l.). For non-halogenated solvents the C s values are found to be generally higher by an order than those of styrene, but the relative trend is more or less similar in both cases. The transfer characteristics of acrylonitrile with halogenated solvents are, however, in striking contrast with those of all other monomers so far studied. The halogenated solvents such as CCl 4 which are usually extremely high chain-transferring agents are found to be devoid of any special susceptibility to an attack by the free radical of acrylonitrile. It is suggested that the inherent instability of compounds containing the group of >C(Cl)CN is responsible for the above unusual behaviour. The C M and 8 (= k 1/2 t / k v ) for acrylonitrile (60° C) have also been determined and are 2.6 x 10 -5 and 2.8 respectively.

The chain-transfer coefficients, C s = k s / k p of highly purified vinyl acetate for twenty-five solvents at 60° C using azobisisobutyronitrile as catalyst have been measured. The C s values are in most cases higher by an order than that of styrene or methyl methacrylate, though the relative order is more or less the same with all the three monomers. This is in agreement with the view that the free radical preferentially attacks the a-hydrogen. The absolute values of the rate of chain transfer, k s of vinyl acetate are, however, found roughly about one thousand times higher for vinyl acetate in comparison with the other two monomers for most solvents. A chemical explanation based on the stability of the transferred atom in the typical compound of low molecular weight formed by transfer is found to be in agreement with known facts about vinyl acetate and other monomers. The behaviour of chlorinated solvents is found to be rather difficult to understand because of the simultaneous transfer of chlorine and hydrogen, but the general tendency of high transfer with higher chlorine: carbon ratio is maintained. The theoretical foundation of such measurements has been briefly discussed, and the possibility of obtaining C s values by a single-tube experiment in suitable systems has been indicated.