Structural changes induced by γ-rays on model linear ethylene-butene copolymers

Well characterized model copolymers are used to study the effects of ionizing radiation. Linear copolymers of ethylene and butene-1 with uniform chemical microstructure and very narrow molecular weight distributions are irradiated at room temperature with γ-rays from a 60Co source. Changes in the molecular hydrodynamic volume can be readily detected by GPC. Changes in molecular weight averages Msub(n) and Msub(w) are measured by membrane osmometry and light scattering. Cross linking seems to be the main effect of radiation and chain scission is negligible up to the gel point. The very uniform molecular structure and size in the non-irradiated polymer allows for the use of a completely general model to correlate changes in molecular weight averages and branching. The model is suitable for linear polymers with reactive groups randomly distributed along the chain, and contains no simplifying approximations. (author)