Polymerization by 7-ray irradiation

As mentioned previously, irradiation of suitably reactive bulk (liquid) monomers with 7-rays from a ° Co soiurce can initiate cationic polymerization [37], i.e. 

A number of monomers has already been investigated, e.g., cyclo-pentadiene [86], styrene [89, 93], a-methylstyrene [87, 89, 95], formaldehyde [94], alkyl vinyl ethers [85, 89], isobutene [84], nitroethylene [96] and also the cyclic monomer cyclohexene oxide [97]. For most of these reliable quantitative data is now available. Because the number of active centres formed is small all of these systems are particularly susceptible to traces of impurities, especially water and spurious basic materials. Indeed much of the early data [82, 83] from 7-ray initiation was confused because of the use of relatively wet monomers. Furthermore the intrinsic lifetime of a free cation is limited because the 

Rates of radiation induced polymerizations are normally determined by dilatometric [85] or gravimetric [84] experiments. Some of the first quantitative results from cyclopentadiene [86] and a-methylstyrene [87] were obtained by competitive kinetic methods, based on the retarding effect of ammonia and amines. This approach tends to yield maximum values for Rp. More recently, however, a procedure combining stationary state kinetic and conductance measurements has been described [88, 89], and further refined [85]. Because the ions generated by 7-ray irradiation have a transient existence, the kinetic treatment leads to expressions which are very similar to those derived for homogeneous free radical polymerizations [90]. A simplified version of the kinetic scheme is as follows  

Gi = 100 eV yield of free ions (excluding geminate recombinations) 

Assuming a stationary state concentration of free ions. 

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