Development of Poly(ionic liquids) Based on Mepiquat Chloride with Improved Rainfastness and Long-Lasting Activity on Growth Regulation of Cotton Plant

Abstract

As one of the plant growth regulators, mepiquat chloride (MC) has become one of the most useful tools to manage plant geometry during cotton growth and development. Since it is highly water-soluble and needs to be applied repeatedly during cotton growth, there is an urgent need to design a novel effective formulation for reducing unwanted loss of MC and prolonging its effective duration. Polymerized ionic liquids (PILs), as a particular class of ionic liquids are composed of a polymeric backbone and an IL species in each monomer repeating unit, which exhibits excellent physical and chemical properties. In this work, PILs based on MC (MPILs) were prepared by the acid–base neutralization between poly(acrylic acid) (PAA) and N,N-dimethylpiperidinium hydroxide derived from MC and were characterized by scanning electron microscopy (SEM), 1H NMR, Fourier transform infrared spectroscopy (FTIR), and UV–vis spectroscopy. The results showed that the N,N-dimethylpiperidinium cation was stably ionic-paired with PAA when the molar ratio of PAA to N,N-dimethylpiperidinium hydroxide was 10:6. MPILs based on MC were endowed with the properties of polymer, and N,N-dimethylpiperidinium cation could be released in a limited manner by attractive forces between oppositely charged ions. Compared with MC, MPILs had higher retention on cotton leaves and exhibited better rainfastness. The control efficacy on the lateral branch length of the cotton plant using MPILs once was almost the same as that using MC twice at dose of 150 g AI ha–1 in the same period. The prepared MPILs showed a long-lasting activity in controlling the lengths of lateral branches and height of the cotton plant and made cotton plant type structures more compact than MC. Thus, this work makes contributions to optimize the application of MC by reducing the frequency of using MC, and MPILs demonstrated a great potential in MC application in the future.