pH-Driven Conformational Switching of Quinoxaline Cavitands in Polymer Matrices

Published as part of the Cluster Synthesis of Materials

Abstract

While pH-driven interconversion of tetraquinoxaline cavitands (QxCav) from vase to kite conformation has been extensively studied both in solution and at interfaces, cavitands behavior in solid matrices is still unexplored. Therefore, the synthesis of a new class of quinoxaline cavitand based copolymers is here reported; a soluble linear poly(butyl methacrylate) (PBMA) and an insoluble cross-linked polydimethylsiloxane (PDMS), ensuring a convenient incorporation of the switchable unit, were chosen as polymer matrices. Conformational studies, performed both in solution and at the solid state, confirmed the retention of vase → kite switching behavior when moving from monomeric units to polymeric structures.

Key words

pH-responsive polymers - tetraquinoxaline cavitands - conformational switching - PDMS - PBMA

• References and Notes

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• 21 Preparation of PBMA-3 In a Schlenk tube, n-butyl methacrylate (0.242 mL, 1.52 mmol) was added to a solution of cavitand 3 (0.027 g, 0.015 mmol) in 2 mL of toluene. The mixture was degassed and heated at 70 °C, then AIBN (0.005 g) was added. The mixture was maintained at 70 °C for 12 h, then cooled at room temperature. The copolymer was recovered by precipitation in MeOH followed by trituration in the same solvent. Polymer PBMA-3 was obtained as a white solid (yield 48%) ¹H NMR (400 MHz, CDCl₃): δ = 8.67 (2 H, Ha), 8.25–8.08 (6 H, Hf + Hb), 7.82 (6 H, Hc + Hd), 7.54 (1 H, He), 7.44 (2 H, He), 7.25 (5 H, Hg + He), 5.57 (m, 4 H, CHCH₂), 4.47 (4 H, Ar(C=O)OCH ₂CH₂), 4.0 (OCH _2,PBMACH₂), 2.29 (8 H, CHCH ₂), 2.1–1.7 (-CH _2,PBMA-C(C=O)CH₃), 1.6 (-CH₂-C(C=O)CH _3,PBMA + OCH₂CH _2,PBMA), 1.4 (OCH₂CH₂CH _2,PBMA), 1.0–0.8 (CH₂CH _3,PBMA) ppm (see Figure S9 in the Supporting Information).
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