Soluble and Processable Single-Crystalline Cationic Polymers

Single-crystal-to-single-crystal(SCSC) polymerizationoffers aneffective protocol for the environmentally friendly preparation ofpolymer single crystals (PSCs) with extremely high crystallinity andvery large molecular weights. Single-crystal X-ray diffraction (SCXRD)serves as a powerful technique for the in-depth characterization oftheir structures at a molecular level. Hence, a fundamental understandingof the structure-property relationships of PSCs is within ourreach. Most of the reported PSCs, however, suffer from poor solubility,a property which hampers their post-functionalization and solutionprocessability when it comes to practical applications. Here, we reportsoluble and processable PSCs with rigid polycationic backbones bytaking advantage of an ultraviolet-induced topochemical polymerizationfrom an elaborately designed monomer that results in a multitude ofphotoinduced [2 + 2] cycloadditions. The high crystallinity and excellentsolubility of the resulting polymeric crystals enable their characterizationboth in the solid state by X-ray crystallography and electron microscopyand in the solution phase by NMR spectroscopy. The topochemical polymerizationfollows first-order reaction kinetics to a first approximation. Post-functionalizationof the PSCs by anion exchange renders them super-hydrophobic materialsfor water purification. Solution processability endows PSCs with excellentgel-like rheological properties. This research represents a majorstep towards the controlled synthesis and full characterization ofsoluble single-crystalline polymers, which may find application inthe fabrication of PSCs with many different functions.

Automated summary

Single-crystal-to-single-crystal (SCSC) polymerization is an effective method for environmentally friendly preparation of polymer single crystals (PSCs) with high crystallinity and molecular weights. Solubility and solution processibility are major challenges for practical applications of PSCs, but this study successfully synthesized soluble and processable PSCs with rigid polycationic backbones. The resulting polymeric crystals have excellent solubility, crystallinity and rheological properties, and can be characterized using various techniques.