Fabrication of microgels via supramolecular assembly of cyclodextrin-containing star polycations and oppositely charged linear polyanions

Abstract

In this work, we report a novel microgel composed of star-like polycations and well-defined linear polyanions via ionic interaction. The polycations, the β-CD-g-PDMA star polymers, were prepared via an ATRP method using a derivative of β-cyclodextrin (β-CD) as a macroinitiator to graft 2-(N,N-dimethyamino)ethyl methacrylate (DMAEMA, or DMA for short) with different lengths. The polyanions, including di- and tri- block copolymers (MePEG-b-PMAA₆₀ and PMAA₃₀-b-PEG-b-PMAA₃₀), were first prepared via oxyanion-initiated polymerization of tert-butyl methacrylate (tBMA) using the potassium alcoholate of MePEG or PEG as macroinitiators, and then obtained by carrying out hydrolysis of the PtBMA block to yield the PMAA block. The star polymers and the oppositely charged linear copolymers were characterized by ¹H NMR, GPC and FT-IR. The results obtained from TEM and DLS show that the cationic and the anionic polyelectrolytes can self-assemble into micelles, respectively. The polyion complex microgels formed by ionic interaction between the polycation and the polyanions have been proved by SEM, TEM, DLS and rheology testing. Interestingly, the self-assembled morphologies of the polyion complex microgels were different when the chemical structures of the polyanions were a MePEG-b-PMAA₆₀ diblock copolymer or a PMAA₃₀-b-PEG-b-PMAA₃₀ triblock copolymer. We have proposed a self-assembly mechanism to give an explanation for the formation of different complex microgels in the presence of different polyanions (i.e. di- or tri- block copolymer). As the hydrophobic cavity of β-cyclodextrin in the star polymer can interact with appropriately sized guest molecules to form host–guest inclusion complexes, the resultant microgels will have potential applications in drug delivery, especially for oil-soluble drugs.