The effect of radiation on poly-α-methylstyrene

Degradation studies on poly‐α‐methylstyrene at 25°C. under vacuum and in hydrogen and oxygen were carried out with the use of a Co60 gamma source. The degradation results are explained as a random breaking of skeletal chain bonds accompanied by a depropagation of the resulting fragments. The termination step for depropagation is considered as a chain transfer of the degrading radical to the produced monomer cloud, the monomer radical thus formed repolymerizing to some extent prior to termination. The necessary relationships are derived which permit the evaluation of the G‐value for bond scission, the kinetic chain length for depropagation from the resulting Mn and Mw values, and the unsaturation produced. The determined G‐values for chain scission are 0.25 in vacuum and hydrogen, 0.16 in air, and 0.08 in oxygen, the gases being at a pressure of one atmosphere. The number of monomer units split off per break was found to be 100 in vacuum, 50 in hydrogen, and essentially zero in the presence of oxygen. It is believed that hydrogen and oxygen terminate the depropagating radical, reducing the kinetic chain length. The reduction in the G‐value for chain scission in the presence of oxygen may be due to either recombination of the terminal peroxide groups formed or deactivation of the chain prior to cleavage. The G‐values for volatile products at room temperature are listed, the important ones being G(H2) = 0.035 and G(CH4) = 0.003.