Preparation and UCST-Type Phase Behaviours of Poly(γ-4-methylbenzyl-L-glutamate) Pyridinium Tetrafluoroborate Conjugates in Methanol or Water

Abstract

Polymers with ionic liquid (IL) moieties can undergo thermally induced solution phase transitions by adjusting the balance of hydrophilicity and hydrophobicity between the cations and anions of the IL moieties, thus making them attractive candidates towards various applications such as separation, sensing, and biomedicine. In the present study, a series of poly(γ-4-methylbenzyl-l-glutamate) pyridinium tetrafluoroborate conjugates (P1–P4) containing various pyridinium moieties (i.e. pyridinium, 2-methylpyridinium, 3-methylpyridinium, and 4-methylpyridinium) were prepared by nucleophilic substitution between poly(γ-4-chloromethylbenzyl-l-glutamate) and pyridine or methylpyridines with different substituent positions, followed by ion-exchange reaction in the presence of NaBF4. 1H NMR spectroscopy and Fourier transform infrared spectroscopy analyses confirmed the molecular structures of P1–P4. 1H NMR analysis additionally revealed that P1–P4 showed high grafting efficiency in the range of 93–97 %. P1, P3, and P4 exhibited reversible UCST-type phase behaviours in both methanol and water, whereas P2 showed a reversible UCST-type phase behaviour in water only. Variable-temperature UV-visible spectroscopy was used to characterize the solution phase behaviours and UCST-type phase transition temperature (Tpt) values of P1–P4, which were in the range of 24.9–37.2°C in methanol (3 mg mL–1) and 40.9–55.7°C in water (10 mg mL–1). Tpt decreased significantly with decreasing polymer concentrations.