Micellization and gelatinization in aqueous media of pH- and thermo-responsive amphiphilic ABC (PMMA₈₂-b-PDMAEMA₁₅₀-b-PNIPAM₆₅) triblock copolymer synthesized by consecutive RAFT polymerization

Abstract

The multi-stimuli-responsive amphiphilic ABC triblock copolymer of poly(methyl methacrylate)-block-poly [N,N-(dimethylamino) ethyl methacrylate]-block-poly(N-isopropylacrylamide) (PMMA-b-PDMAEMA-b-PNIPAM) was synthesized by sequential reversible addition-fragmentation chain transfer (RAFT) polymerizations. Due to the pH-and thermo-responsive blocks of PDMAEMA and thermo-responsive blocks of PNIPAM, the copolymer solution properties can be manipulated by changing the parameters such as temperature and pH, and it formed diverse nanostructures and had gel behavior in different conditions. In detail, when the pH was below 7.3, the pK a of DMAEMA, tertiary amino groups were protonated, the polymer micellar solution like weak gel changed into free-standing gel at around 40 C even at a low concentration of 2 wt%. Further, the gel behavior and morphology of the system were studied by rheology, turbidimetry measurements, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. When the pH was above the pK a , the triblock copolymer selfassembled into diverse micellar structures including shell-core, corona-shell-core and shell-shell-core nanoparticles as the temperature increased, but no free-standing gelation. The two-step thermoresponsive behavior, corresponding to the different LCSTs of PNIPAM block and DMAEMA block, was evidenced by turbidity analysis. The assembled structures rapidly collapsed due to the enhanced hydrophobic interaction when the temperature further increased. Dynamic light scattering (DLS) was used to confirm the transitions.

Characterization of PMMA-b-PDMAEMA aggregates in aqueous solutions

“…PDMAEMA-based copolymers usually have an LCST that is evident even when aggregated as micelles. Above this temperature, corona dehydration can lead to load release, micelle aggregation/precipitation, or both [19]. As temperature effects are also affected by medium acidity, pH can be used together with the temperature for controlling drug release [20].…”

Renewable Fabric Surface-Initiated ATRP Polymerizations: Towards Mixed Polymer Brushes

“…Figure 1 presents the spectra of unmodified PA fibers and PMMA or PS modified fibers. The presence of the strong peak at 1735 cm −1 is assigned to the occurrence of an ester carbonyl group from poly(methyl methacrylate) [37] (Figure 1a). In the case of PS, numerous peaks characteristic for PS overlap with the PA support (i.e., the peak at the range of 1600 cm −1 ) associated with the presence of aromatic protons of styrene units, except the weak peak at 3100-3000 cm −1 which is also associated with aromatic protons of styrene [38] (Figure 1b).…”

“…Figure 1 presents the spectra of unmodified PA fibers and PMMA or PS modified fibers. The presence of the strong peak at 1735 cm −1 is assigned to the occurrence of an ester carbonyl group from poly(methyl methacrylate) [37] (Figure 1a). In the case of PS, numerous peaks characteristic for PS overlap with the PA support (i.e.…”

Active control of properties of concrete: a (p)review

“…by pH control [ 96 ] Sorption control of water vapour of e.g. electro-responsive polypyrole film [ 98 ] Control of solubility, often by changing temperature [ 99 ] Changing the nature of a complex molecule from hydrophilic to hydrophobic, also enabling control over the micellization process [ 97 ] Changing the self-assembly, e.g. CO 2 and redox-stimulated transformation of entangled worms to rodlike micelles [ 85 ] Changing the orientation of the polymers, e.g.…”