Quantifying tie-molecule content in semicrystalline polymers

Tie molecules bridging adjacent crystalline lamellae in semicrystalline polymers strongly impact mechanical properties, but they remain difficult to characterize. We demonstrate a new method of measuring tie-chain content: applying equilibrium swelling theory to small-angle neutron scattering patterns from semicrystalline polyethylene films whose interlamellar amorphous regions are swollen with deuterated organic solvent in a vapor-flow sample environment. To aid in validating the measurement, measured tie-chain content is compared with a primary structural parameter (PSP2) that is calculated from molecular architecture and correlates with slow crack growth behavior. Agreement is favorable for a linear polyethylene and a series of ethylene-hexene copolymers. Recent applications of the technique are also discussed.