Macromolecular Nanocapsule Derived from Hyperbranched Polyethylenimine (HPEI): Mechanism of Guest Encapsulation versus Molecular Parameters

Abstract

Nanocapsule derived from hyperbranched polymer bears a number of active functional groups in the core; such a structure feature renders it possible to meticulously engineer the core of the nanocapsule and thus provides a unique opportunity to evaluate the structure-property relationship. Here the amino protons of HPEI (M n ) 10 000 Da) are 15%, 30%, 60%, and 86% alkylated with 2-dodecyloxymethyloxirane, leading to core-shell structured amphiphilic macromolecules (CAMs) with such different shell density as HP(EI-OH 0.15 C12 0.15 ) (3a), HP(EI-OH 0.30 C12 0.30 ) (3b), HP(EI-OH 0.60 C12 0.60 ) (3c), and HP(EI-OH 0.86 C12 0.86 ) (3d), respectively. The cores of 3a-3d are further chemically modified by complete alkylation of the residual amino protons with propylene oxide, leading to HP(EI-OH 1 C12 0.15 ) (4a), HP(EI-OH 1 C12 0.30 ) (4b), HP(EI-OH 1 C12 0.60 ) (4c), and HP(EI-OH 1 C12 0.86 ) (4d), respectively. Nanocapsule with thick shell is also obtained by alkylation of HPEI with epoxy polystyrene (M n ) 1800), leading to HPEI with 15% (HP(EI-OH 0.15 PS 0.15 ), 7a), 30% (HP(EI-OH 0.30 PS 0.30 ), 7b), and 60% (HP(EI-OH 0.60 PS 0.60 ), 7c) of the amino protons being alkylated. Water-soluble, anionic dyes can be encapsulated by these CAMs. It is found that 7a-7c exist as unimolecular inverted micelles in the tested range while 3a-3d and 4a-4d exist as aggregates in chloroform, indicating that a thick shell is crucial to the nature of unimolecular micelle. It is also found that the guest releasing ability is dependent on the nature of the functional groups in the core but independent of the shell density; thus, encapsulation of methyl orange by 3a-3c is reversible, while that by 4a-4c is irreversible. Congo red can be encapsulated by the aggregate of 3a-3d or 4a-4d, but excessive Congo reds cause precipitation of the aggregate. Finally, it is noticed that the molecule recognition property is also dependent on the nature of the functional groups in the core but independent of the shell density and shell thickness; as a result, a CAM with a designed core can highly selectively encapsulate a guest from a mixture.

Selective Encapsulation of Ionic Dyes by Core/Shell Amphiphilic Macromolecules Derived from Hyperbranched Polyethylenimine: Properties through Structures

“…The CAMs were synthesized in a way similar to previous methods [17,19] and their structures are outlined in Scheme 1.…”

“…[19] To understand why some dyes are reluctant to be encapsulated while some can be readily encapsulated by a CAM, a diverse range of large, ionic and water-soluble dyes ( Figure 1) were tested using CAM 1b at different pH values. The results are collected in Table 1.…”

“…[16,17] A CAM derived from hyperbranched polymer is known for a randomly branched structure and a roughly defined topology, but the electronic properties of such a CAM are readily adjustable because of the dense functional groups randomly distributed throughout the core. The core engineering of CAMs has led to successful separation of some complex ionic mixtures, [18][19][20] including compounds which have very similar structures. [16,17] Now there are several issues that need clarify.…”

“…were synthesized as reported previously (Scheme 1). [17,19] Characterization UV-vis spectra were recorded on a 760 CRT UV-vis spectrometer (Shanghai analytical instrument factory). 1 H and 13 C NMR spectra were recorded on Bruker instrument (at 400 MHz for 1 H and 100 MHz for 13 C, respectively) with TMS as a reference.…”

Miktoarms hyperbranched polymer brushes: One-step fast synthesis by parallel click chemistry and hierarchical self-assembly

“…From this point of view, molecular brushes offer us a good opportunity to access biomimetic polymers. Besides, molecular brushes can also be used as single molecular templates for inorganic nanoparticles formation and they also have potential application in fields of solubilizer, catalysis and drug delivery [6][7][8][9][10].…”