Poly(ε‐caprolactone) Single Crystals with Different Aspect Ratios Mediated by Counterion Exchange on the Basis of Hofmeister Series

Abstract

AbstractAlthough polymeric single crystals fabricated from self‐assembly of block copolymers are reported, preparation of single crystals with different aspect ratios still remains a major challenge. In this work, a facile way is demonstrated to prepare poly(ε‐caprolactone) based single crystals with tunable aspect ratios through simple counterion exchange on the basis of the Hofmeister series. Briefly, after ion exchange from Brˉ (an ion‐containing triblock copolymer, poly(ethylene oxide)‐b‐poly(ε‐caprolactone)‐b‐poly(quaternized 2‐(dimethylamino)ethyl methacrylate)/ethyl bromide (PEO‐b‐PCL‐b‐qPDM‐Br)) to more hydrophobic anions, Iˉ, SCNˉ, PF6ˉ and OTfˉ, respectively, morphological transitions from spheres to wormlike micelles and sphere to 2D platelet structure with an increasing aspect ratio are observed. The morphological transition depends on the essential hydrophilicity of the qPDM‐X segment and increasing crystallinity of the PCL core caused by ion exchange. These findings provide a facile approach to the preparation of polymeric single crystals with tunable aspect ratios.