Selective dissolution as a tool for detecting spatial variations in the metastability within lamellar polymer crystals

Abstract

The dissolution of polymer crystals often proceeds at rates varying in time and space. Here, using low molecular weight poly(ethylene oxide) as a model polymer, we exploit step-wise selective dissolution for unveiling how spatial variations in metastability are generated during the growth of lamellar polymer single crystals. The dissolution velocity along defined crystal faces is constant, but ca. 5 times faster for rough than for smooth faces. From the temperature dependence of dissolution, we derive detachment energies of 420 ± 40 kJ/mol and 650 ± 50 kJ/mol for rough and smooth faces, respectively, suggesting that on a rough face polymer chains have ca. 1/3 less neighboring molecules to interact with. The observed high values of the activation energy indicate that, for dissolving a polymer crystal, the progressive detachment of whole chains is indispensable. Our study reveals a strong relation between growth kinetics and the resulting metastability of polymer crystals.