Diagnosing long-chain branching in polyethylenes

We propose a novel method for assessing sparse long-chain branching in synthetic polymers such as high-density polyethylene at levels far below the limits of detectability by the usual methods of solution viscometry, size-exclusion chromatography, and NMR spectrometry on solutions. The new method exploits the extreme sensitivity of melt Newtonian viscosity to random branching architecture, along with the systematic phenomenological description thereof developed recently in fundamental studies by Lusignan et al. The method satisfies the only validation criterion presently available to us: it finds long-branch contents in quantitative agreement with stoichiometric yields calculated for several series of linear precursor polyethylenes treated with very low levels of peroxide. (C) 1999 Elsevier Science B.V. All rights reserved.