NMR approach to the characterization of the swelling process of polyethylene networks

Statistical properties of irregular polyethylene networks of different cross-link densities were probed by determining their gel fraction and equilibrium swelling ratio and by measuring the magnetic relaxation of protons. Experimental results were in agreement with the description of the vulcanization of linear chains within a percolation framework leading to a G exp --1 dependence of the equilibrium swelling ratio Q sub m . A parametrized assay function was formed to fit the observed relaxation functions. The fit yielded the second and fourth moment behavior of the resonance line. Evidence for a two-step swelling behavior of the PE networks in the presence of a swelling agent (xylene) is given. The second moment of the relaxation functions observed in networks swollen at equilibrium was shown to be independent of the cross-link density. This result was assigned to the existence of a submolecule perceived from NMR with a size smaller than the average distance between cross-links in the polymer gel. 10 ref.--AA