Complex Formation in the Sulfobetaine-Containing Entirely Ionic Block Copolymer/Ionic Homopolymer System and Their Temperature Responsivity

Abstract

The behavior of micelle formation in the sulfobetaine-containing entirely ionic block copolymer/ionic homopolymer system and its functional expression (temperature responsivity) were investigated. Poly(sulfopropyl dimethylammonium propylacrylamide) was used as the sulfobetaine, poly[3-(methacrylamido)propyl trimethylammonium chloride] was used as the cationic polymer, and poly(pstyrenesulfonic acid sodium salt) was used as the anionic polymer. The changes in transition temperature with the concentration and the behavior of micelle formation in the block-/cationic homopolymer and block-/anionic homopolymer system were compared and examined by transmittance, dynamic light scattering, atomic force microscopy, and 1 H nuclear magnetic resonance. Only block-/cationic homopolymer systems with a core−shell (polyion complex−sulfobetaine) structure showed temperature responsivity of upper critical solution temperature type, and the responsiveness was dependent on the concentration. On the other hand, the block-/ anionic homopolymer system had a core−shell structure at a concentration of 0.05 wt %, but temperature responsiveness was not observed at this concentration. At higher concentrations, electrostatic attraction caused the anionic homopolymer and block copolymer to interact as a whole, resulting in a loss of responsiveness. When the ionic homopolymer had a higher degree of polymerization than the sulfobetaine, it could not form a core−shell structure by interacting with the sulfobetaine and ionic polymer moieties of the block copolymer, thus resulting in the loss of responsiveness. The block-/ionic homopolymer system prepared by the reforming method through dialysis formed uniform and small micelles but lost responsiveness due to morphological stability and electrostatic interaction between the block copolymer and ionic homopolymer.

Effect of Hydrophobicity and Salt on the Temperature Responsiveness of Polymeric Micelles Consisting of Hydrophobic and Sulfobetaine Chains

“…The PSPP homopolymers were synthesized by the reversible addition-fragmentation chain transfer (RAFT) technique. The synthesis was carried out by mixing each monomer, CTA, and initiator (ACVA) in various molar ratios as reported previously. , The degree of polymerization (DP) and dispersity ( Đ ) of the obtained solid homopolymers were evaluated by GPC. Homopolymers thus obtained were confirmed by 1 H NMR.…”

“…Zwitterionic polymers have been studied in various fields such as polymer brushes, − gels, − surfactants, − polymeric micelles − or vesicles, , and energy materials ,, because they have anions and cations in the same molecules. − Their structural specificity not only causes a behavior different from existing ionic polymers in the presence of salts ,, but also their property of suppressing protein adsorption and blood cell adhesion. − The cation moieties of zwitterionic polymers are in general quaternary ammonium cations and are classified into carboxy-, phospho-, and sulfobetaine according to the functional group of the anionic moiety. − Among them, two types of betaine polymers show stimulus responsiveness: carboxybetaine shows pH response, , and sulfobetaine exhibits upper critical solution temperature (UCST)-type temperature response. − The pH response behavior of carboxybetaine is due to the protonation of the carboxyl group by acid, , and the temperature response behavior of sulfobetaine is due to the formation of intra- or intermolecular salts and their dissolution. − …”

“…An amphiphilic block copolymer consisting of a hydrophilic chain and a hydrophobic chain forms a polymer micelle by the hydrophobic interaction of the hydrophobic block in the solvent. , On the other hand, a novel self-assembly called polyion complex (PIC) micelle forms a core by the electrostatic interaction between polyanions and polycations and the increase in entropy due to the release of counterions by aggregation. − Both can be applied to a drug delivery system (DDS) using a polymer having a stimulus responsivity as a shell and have been widely studied. − Their responsiveness and morphology can be controlled by temperature, − , concentration, − solvent, , pH, , mixing ratio, block ratio, etc.…”

“…We previously reported a PIC micelle with a betaine chain that was like a shell, which is responsive to stimuli. − In particular, in the case of PIC micelles using sulfobetaine as a shell, it was clarified that the transition temperature can be controlled by adjusting the degree of polymerization (DP) of sulfobetaine block, the concentration of the polymer aqueous solution, and the concentration of the added salt. − In addition, the size and uniformity of PIC micelles can be controlled by the reformation method by dialysis …”

Thermo-Responsive Polyion Complex of Polysulfobetaine and a Cationic Surfactant in Water

“…Some of them exhibit pH-responsive [ 17 , 18 , 19 , 20 , 21 ] and thermo-responsive behaviors [ 22 , 23 , 24 , 25 , 26 , 27 ] and biocompatibility [ 28 , 29 , 30 ]. Especially, polysulfobetaines show upper critical solution temperature (UCST) behavior in water [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. UCST is the critical temperature above which the mixture solution is miscible, meaning that a single phase exists for all of the composition, and under critical temperatures, the solution becomes turbid because the solute cannot dissolve in solvent.…”