Ionization Of Amphiphilic Acidic Block Copolymers

Abstract

The ionization behavior of an amphiphilic diblock copolymer poly(n-butyl acrylate(50%)-stat-acrylic acid(50%))(100)-block-poly(acrylic acid)(100) (P(nBA(50%)-stat-AA(50%))(100)-b-PAA(100), DH50) and of its equivalent triblock copolymer P(nBA(50%)-stat-AA(50%))(100)-b-PAA(200)-b-P(nBA(50%)-stat-AA(50%))(100) (TH50) were studied by potentiometric titration either in pure water or in 0.5 M NaCl. These polymers consist of a hydrophilic acidic block (PAA) connected to a hydrophobic block, P(nBA(50%)-stat-AA(50%))(100), whose hydrophobic character has been mitigated by copolymerization with hydrophilic units. We show that all AA units, even those in the hydrophobic block could be ionized. However, the AA units within the hydrophobic block were less acidic than those in the hydrophilic block, resulting in the preferential ionization of the latter block. The preferential ionization of PAA over that of P(nBA(50%)-stat-AA(50%))(100) was stronger at higher ionic strength. Remarkably, the covalent bonds between the PAA and P(nBA(50%)-stat-AA(50%))(100) blocks in the diblock or the triblock did not affect the ionization of each block, although the self-association of the block copolymers into spherical aggregates modified the environment of the PAA blocks compared to when PAA was molecularly dispersed.

High-Capacity Drug Carriers from Common Polymer Amphiphiles

“…In a macromolecular context, hydrogen bonding interactions with poly(acrylic acid) have been reported to guide layer-by-layer assembly in water 20,21 as well as mucoadhesion of hydrogels. 22 Colombani and others have shown that p K a can be significantly elevated in polymer acids, 23 similar to p K a shifts found in proteins and nucleic acids. 24,25 We hypothesized that limited or altered ionization of acidic-hydrophobic diblock polymers could result in assembly stabilization via interchain hydrogen bonding and increased chain hydrophobicity.…”

“…Indeed, PAA domains can have p K a ’s in the range of 5–6.5, significantly shifted toward neutral by the local macromolecular environment relative to small molecule carboxylic acids. 23 Global ionization state of poly(acrylic acid) (5.6 kDa standard) and p[(AA) 48 - b -(nBA) 50 ] was interrogated using ATR-IR spectroscopy in deuterated saline water, adjusted to acidic, neutral, and basic pD at constant ionic strength (Figure 2). The PAA standard was chosen to benchmark expectations for known polyacids outside the context of diblock amphiphile assembly.…”

Tuning the aggregation behavior of pH-responsive micelles by copolymerization

“…27 Moreover, for the system studied herein both monomers in both blocks can be ionized. Therefore, we explored how the microstructure of the diblock copolymers altered their ionization behavior via potentiometric titration experiments.…”

“…Subsequently these solutions were back titrated with 0.1 M NaOH to allow for the determination of the evolution of ionization degree, α, with respect to pH. 27,42 Comparing the ionization behavior of the diblock copolymers (from 1 to 4) we observe the pH range in which ionization occurs (Fig. 1).…”

Slow dynamics in transient polyelectrolyte hydrogels formed by self-assembly of block copolymers

“…The polymer was dissolved in pure water containing sufficient NaOH so that all acrylic acid groups were ionized [57]; i.e., the degree of ionization (α) was unity. The solutions were filtered through 0.2 μm pore size GHP Acrodisc filters.…”