Synthesis of double hydrophilic block copolymers and induced assembly with oligochitosan for the preparation of polyion complex micelles

Abstract

This paper reports on the polyion complex micelles (PIC micelles) formed between neutral-ionizable double hydrophilic block copolymers (DHBC), poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA), and oligochitosan, a natural polyamine. The controlled synthesis of PEO-b-PAA polymers was achieved by atom transfer radical polymerization (ATRP) of tert-butyl acrylate with u-bromide-functionalized PEO macroinitiators (M w ¼ 2000 and 5000 g mol À1 ) and the subsequent deprotection reaction under acidic conditions. A series of copolymers with a narrow molecular weight distribution (M w /M n # 1.2) and varied PAA block lengths was synthesized. Capillary electrophoresis (CE) was shown to unambiguously prove the blocky structure of the copolymers. It also showed that about 60%of the sodium counter ions were condensed onto the polyacrylate block in the pure diblock copolymer solution, which is consistent with the formation of polyion complex micelles triggered by counter-ion release in the presence of oligochitosan. The formation of oligochitosan/PAA-PEO core-corona micelles has been investigated by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). A minimum length of the PAA block is necessary to ensure micelle formation. The range of pH, where PIC micelles form, critically depends on the PAA block length, which also determines the size of the micelles. Micelles can be dissociated at ionic strength above 0.4 mol L À1 . Since these PIC micelles have been used as recyclable structuring agents for the formation of ordered mesoporous materials, the reversibilty of the assembling process was studied upon pH and ionic strength cyclic variations. A hysteresis of stability was observed at low pH, probably due to hydrogen bonding.

Physicochemical properties of pH-controlled polyion complex (PIC) micelles of poly(acrylic acid)-based double hydrophilic block copolymers and various polyamines

“…The average power exponent of about 2.5 was higher than the one obtained in the case of micelles comprising linear PEO-b-PAA copolymers (α01.7). For the latter, the corona could be described by an excluded volume model taking into consideration selfavoidance and mutual avoidance of the corona chains [12]. The PAMPEO chains in the corona were in a denser configuration than that of linear PEO chains, in agreement with the comb-like architecture of the PAMPEO blocks.…”

“…The characteristics of the nanostructures obtained here were consistent with the results from Laschewsky et al [26] on similar systems, from Sanson at al. [27] on DHBC-based coordination complex micelles, and from Reboul et al [12] on polyamine PIC micelles based on linear PAA-b-PEO DHBC polymers.…”

“…Their values ensured the existence of a pH window where both polymers, DHBC and polyamines, were concomitantly present in their ionized forms, a prerequisite for the formation of PIC micelles, as illustrated in Scheme 1. The pH window is approximately defined by the pK a of PAA 48 -b-PAMPEO 36 (pK a 05.5) and that of the polyamine, as previously observed using similar systems based on PAA-b-PEO block copolymers [8,12,13,24,25]. The pH ranges of micellization were experimentally evidenced by DLS by plotting the scattered light intensity of the various DHBC/ polyamine mixtures as a function of pH for the different polyamine systems (Fig.…”

“…Any parameter influencing the electrostatic interactions between the two macromolecules, such as the ionic strength, the mixing fraction, or pH, can be used to control the phase separation, especially when weak acids and bases constitute the polyelectrolyte blocks. Recently, some of us developed environmentally interesting applications based on the reversibility of PIC micelle formation in the field of mesoporous inorganic materials using the DHBC complex micelles as new silica structuring agents [8,12,13]. These studies revealed that the properties of the resulting hybrid materials strongly depended on the nature of the homo-polyelectrolyte (a polyamine) chosen for the complexation step with a poly(acrylic acid)-b-poly(ethylene oxide) DHBC.…”

“…Both concur in a controlled associative phase separation, known as complex coacervation [3,6,11], provided certain requirements are met, in particular respecting as much as possible an overall charge neutrality. The presence of the neutral block of the DHBC, usually a polyethylene oxide block (PEO), ensures that the normally insoluble electrostatic complex is sterically stabilized in solution as a micellar assembly [8,12,13]. A considerable advantage of such polyion complex (PIC) systems is that the phenomenon of phase separation can be tuned in water.…”