The kinetics of the polymerization of aqueous solutions of acrylamide initiated by 50 Kvp X-rays, 220 Kvp X-rays and COG* prays have been investigated. Dose rates ranged from 2-3 x 1014 to 4.6 x 1018 eV 1.-1 sec-1. For concentrations of acrylamide between 0.1 M and 2.0 M the following relations were established : Rp = [mlll-O&s., DPcc [m1]1'17 f -09 1-0.21 f -05 abs.

Various methods have been used, including the chromatographic analysis of non-gaseous products and free radical detection with ferric chloride, to investigate the mechanism of the gOSr----!JOY beta-radiolysis of liquid benzene. The initial G for reduction of FeCl3 is strongly dependent on [FeCI3] and may be as high as 10; it falls rapidly with increasing dose to a constant value of 0866012. It is concluded that the most important primary act leads to the formation of phenyl radicals and hydrogen atoms, together with electronically excited benzene molecules of two types, one with a lifetime of -100 psec tentatively assigned to the 3Blu state and the other, of shorter life, which may be the lBzu state. The C6H5 radicals and H atoms are very reactive towards benzene, and FeC13 scavenges only secondary, less reactive, radicals but can also be decomposed by interaction with a benzene molecule in either state of excitation.Whereas hydrogen and acetylene are the only gaseous products in the radiolysis of liquid, air-free benzene,l-3 the non-gaseous products, often termed " polymer", have been only partially characterized. Gordon, van Dyken and Doumani 3 have shown that the " polymer ", obtained from the W o -y irradiation of benzene, contains a Clz fraction which constitutes 18.8 % w/w of total "polymer", a C18 fraction (57.6 %) and a >CIS fraction (23.6 %). Although biphenyl was the only C12 product positively identified 3 (cf. ref. (4)), four other members of the Cl2 group have been distinguished 5 ; two were positively identified as phenyl cyclohexadiene-2,4 and phenyl cyclohexadiene-2,5, a third is probably phenyl hexatriene and the fourth was not identified. The identity of the c 1 8 and > C18 products is even less certain. There appear to be a large number of CIS products 5 and this fraction may contain " hydrogenated terphenyls and terphenyls ". 3 Values of G(H2), G(C2H2), G(diphenyl), and G(benzene+" polymer "), obtained by several workers, are presented in table 1.

If Rp is the rate of the radiation-induced polymerisation of acrylamide in aqueous sohtions containing metallic ions, M, which terminate the growth of polymer radicals by oxidizing or reducing them, the graph of R$ against Rp [MI always has a linear portion, of which the negative slope is proportional to the rate constant of this termination reaction. Tn addition, from certain of the graphs may be obtained (i) values of GH/COH or GH~o,/(GH+ GOH) in good agreement with established values, and (ii) relative rate constants for the reactions of metal ions with hydrogen atoms or hydroxyl radicals. The A and E factors for the oxidation of polymer radicals by (i) Fe3+ and Cu2+ in H20 and D20

Acidified ferric perchlorate causes linear termination of the Xor y-ray initiated polymerization of acrylamide in water. The Fe3+OH-ion appears to terminate polymer chains more efficiently than does the F e i l ion, the respective termination rate constants being kS = 1.1 & 0.6 x 104 1. mole-lsec-1 and k4 = 2.0 f 0.6 x lo3 1. mole-lsec-1. Measurement of the yield of ferrous ion led to an evaluation of the yield of initiating radicals from 50 Kvp X-rays as (GOH + GH) > 6.9. Under conditions of exclusively

No abstract

The chemical changes resulting fom the 6OCo pirradiation of pure DMF and solutions of ferric chloride, acrylonitrile or ferric chloride+acrylonitrile in DMF have been investigated. The distribution of the radiolysis products, carbon monoxide, hydrogen, methane and dimethylamine, suggest that fission of the carbonyl-nitrogen and nitrogen-methyl bonds are the most probable reactions. G(-FeC13) has a maximum value of 12-4 rt 1.0. EXPERIMENTAL MATERIALSMay and Baker reagent-grade DMF was purified by being stirred with three separate quantities of phosphorus pentoxide, filtered and distilled under reduced pressure (-20 mm Hg) through a 1-m vacuum-jacketed column packed with Fenske glass helices. The middle fraction of the distillate was dried in vacuo over phosphorus pentoxide before being thoroughly deaerated and distilled into a storage vessel, fitted with break seal entries, which was finally sealed off from the vacuum line.AcRYLoNITRnE.-Hopkin and Williams reagent-grade was washed successively with 10 % aqueous hydroxide, 10 % sulphuric acid, aqueous sodium carbonate and distilled water.

New evidence is presented in support of the suggestion that the 7-ray induced polymerization of liquid isobutene at -78°p roceeds solely by a cationic mechanism. Attempts to polymerize isobutene at -78°with free radicals from the photolysis of diacetyl, benzoin and benzil were unsuccessful but the benzil solution irradiated with ultraviolet light at 77°K. was shown by electron spin resonance measurements to give rise to radicals from the isobutene. Isobutene irradiated in the pure state at a 7-ray dose rate of 7 X 1017 e.v. ml.-1 min.-1 polymerized with ©(-CJIe) = 3.0 ± 1.7 X 102. Solutions of FeCl3, DPPH, benzoquinone and iodine in isobutene were also irradiated with 7-rays. Of these solutes, only benzoquinone reduced the polymerization rate to zero, and DPPH had no significant effect. The effects of FeCls and T2 on the polymerization were complicated by other factors. The measured yields of conversion of the solutes after irradiation were G(-DPPH) = 3.7 ± 0.2, <7(Fe(II)) = 3.0 ± 0.5 and (7(-Q) = 1.5 ± 0.2. The electron spin resonance spectrum of isobutene irradiated with 7-rays at 77 °K. showed the presence of H atoms which disappeared rapidly, and a more stable radical, the spectrum of which consisted of 6 peaks having an over-all spacing of 158 gauss at the operating frequency of 9400 Me. sec.-1. The same six peak pattern was obtained from cyclopropane irradiated with 7-rays at 77 °K. and from a solution of benzil in isobutene irradiated with ultraviolet light at 77°K. It is concluded that the radical responsible for this spectrum is either the cyclopropyl radical or the methyl substituted allyl radical, the latter being the less likely. The most likely initiating ion is considered to be (CH3)3C+, and a mechanism consistent with the available data is proposed.

No abstract