Tunable UCST behaviour of a hydrophobic dialkoxynaphthalene-functionalized homopolymer based on reversible supramolecular recognition

Abstract

Thermoresponsive polymers with reversible phase transition are appealing to various applications. Herein, we designed and synthesized a thermosensitive homopolymer bearing hydrophobic dialkoxynaphthalene moieties as polymer side chains that revealed UCST behaviourin pure ethanol and ethanol/water mixtures. It is reported that the complexation with the tetracationic macrocycle cyclobis(paraquat-p-phenylene) (CBPQT4+) host is strongly dependent on the degree of complexation due to steric hindrance and charge repulsion.Moreover, it was found that the cloud-point temperatures (TCP) of the homopolymer could be modulated by host–guest complexation with CBPQT4+ in alcohol-water solvent mixtures up to 6 equivalents of the host. When heated above theclearance-point temperatures, the homopolymer dissolves, but the host–guest interactions become unstable and are disrupted due to the effect of the solventand the higher temperature. Subsequent cooling led to the collapse of the homopolymer, together with the reformation of the host–guest complexes resulting in a purple opaque solution. The tunable UCST approach may enable practical applications in the biomedical field or interactive smart materials.