NMR observations of drawn polymers. V. Sorption into drawn and undrawn polyethylene

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Abstract
NMR measurements on undrawn polyethylene (PE) samples in contact with a solvent such as C2Cl4 indicate an increase in the mobility of the mobile chain segments as compared to dry samples. Highly drawn PE shows no such effect. This is because Sa, the sorption per unit mass of noncrystalline material present, decreases from 20.9 wt.‐% (dry basis), found for undrawn quenched PE, to 0.63 wt.‐% after drawing (Sa determined at 25°C. and 0.80 vapor activity). Drawing also reduces the segment mobility according to the NMR spectrum. It is shown that these effects are caused by considerable structural changes occurring in the noncrystalline regions of PE upon drawing. Annealing of drawn PE samples at successively higher temperatures leads to a gradual relaxation of the noncrystalline regions towards the state characteristic of undrawn PE. With increasing annealing temperature Sa as well as the mobility approach values found with undrawn PE.