The b-value of polyethylene (PE) is determined 0.9 by the model PE made by gamma-ray irradiation of a linear PE in accordance with the previously reported method. The above is the monodisperse b-value, which is here distinguished from the polydisperse b-value. The former, relevant to a molecular weight (MW)-monodisperse polymer, is proved significantly less than the latter, relevant to a MW-polydisperse polymer, especially in case of trifunctionally branched polymer. Shultz′s numerical solutions of g′(=_??_η_??__br/_??_η_??__l, the ratio of intrinsic viscosities of branched and linear molecules of equal MW) are based-on for the proof. The branch data for low density PE of high pressure-radical polymerization which appeared in the past literatures are reviewed by referring to this results and the first report of this series.

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The reason why the ultimate elongation of gum elastmer decreases by irradiation was studied. The sample used is tetrafluoroethylenepropylene copolymer vulcanized which is a heat resistant elastmer.
The sample was irradiated by a electron beam at room temperature. Cross-linking predominate in the operation. (Case 1) Scission predominant condition (Case 2) was given by irradiation of Co-60 γ ray at 100°C. Alternative irradiation of γ ray and electron beam under above condition can keep the original cross-linking density by the appropriate choice of each of the doses. (Case 3) The three cases mentioned above involve all of the cases of radiation induced aging of elastmers. Therefor, the following explanation for three cases shows the reason why the ultimate elongation of gum elastmer decreases by irradiation.
Case 1. Cross-linking predominant condition.
Ultimate elongation is proportional to -0.5 power of the dose. This fact can be explicable by the model of Buche, i.e. the breaking of a short chain causes another to break and that so on throughout the whole sample.
Case 2. Chain scission predominant condition.
Ultimate elongation increases by irradiation for a certain dose. This fact can understand by the model of Buche. But from a certain dose ultimate elongation does not increase. In the period the structure of the sample turned to be the same structure as the low molecular weight amorphose polymer vulcanized.
Case 3. Rate of cross-linking and scission is the same.
The average chain length does not chainge in the condition. But the distribution of chain length became wider and wider by irradiation. The increase of short chain result the decrease in ultimate elongation.

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