pH- and Photoresponsive Liquid Plasticine.

Liquid marbles (LMs) can be prepared by adsorption of hydrophobic particles at the air-liquid interface of a water droplet. LMs have been studied for their application as microreaction vessels. However, their opaqueness poses challenges for internal observation. Liquid plasticines (LPs), akin to LMs, can be prepared by the adsorption of hydrophobic particles with a diameter of 50 nm or less, at the air-liquid interface of a water droplet. Unlike LMs, LPs are transparent, allowing for internal observation, thus presenting promising applications as reactors and culture vessels on a microliter scale. In this study, the surface of silica particles, approximately 20 nm in diameter, was rendered hydrophobic to prepare hydrophobic silica particles (SD0). A small amount of poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) was then grafted onto the surface of SD0, yielding SD1. SD0 particles exhibited consistent hydrophobicity irrespective of the environmental pH atmosphere. Under acidic conditions, SD1 became hydrophilic due to the protonation of pendant tertiary amines in the grafted PDPA chains. However, SD1 alone was unsuitable for LP preparation due to its high surface wettability regardless of atmospheric pH, attributable to the presence of PDPA-grafted chains. Therefore, to prepare pH-responsive LP, SD1 and SD0 were mixed (SD1/SD0 = 3/7). Upon exposure to HCl gas, these LPs ruptured, with the leaked water from the LPs being absorbed by adjacent paper. Moreover, clear LPs, prepared using an aqueous solution containing a water-soluble photoacid generator (PAG), disintegrated upon exposure to light as PAG generated acid, leading to LP breakdown. In summary, pH-responsive LPs, capable of disintegration under acidic conditions and upon light irradiation, were successfully prepared in this study.

The Effect of Block Ratio and Structure on the Thermosensitivity of Double and Triple Betaine Block Copolymers.

AB-type and BAB-type betaine block copolymers composed of a carboxybetaine methacrylate and a sulfobetaine methacrylate, PGLBT-b-PSPE and PSPE-b-PGLBT-b-PSPE, respectively, were synthesized by one-pot RAFT polymerization. By optimizing the concentration of the monomer, initiator, and chain transfer agent, block extension with precise ratio control was enabled and a full conversion (~99%) of betaine monomers was achieved at each step. Two sets (total degree of polymerization: ~300 and ~600) of diblock copolymers having four different PGLBT:PSPE ratios were prepared to compare the influence of block ratio and molecular weight on the temperature-responsive behavior in aqueous solution. A turbidimetry and dynamic light scattering study revealed a shift to higher temperatures of the cloud point and micelle formation by increasing the ratio of PSPE, which exhibit upper critical solution temperature (UCST) behavior. PSPE-dominant diblocks created spherical micelles stabilized by PGLBT motifs, and the transition behavior diminished by decreasing the PSPE ratio. No particular change was found in the diblocks that had an identical AB ratio. This trend reappeared in the other set whose entire molecular weight approximately doubled, and each transition point was not recognizably impacted by the total molecular weight. For triblocks, the PSPE double ends provided a higher probability of interchain attractions and resulted in a more turbid solution at higher temperatures, compared to the diblocks which had similar block ratios and molecular weights. The intermediates assumed as network-like soft aggregates eventually rearranged to monodisperse flowerlike micelles. It is expected that the method for obtaining well-defined betaine block copolymers, as well as the relationship of the block ratio and the chain conformation to the temperature-responsive behavior, will be helpful for designing betaine-based polymeric applications.

Formation of Polyion Complex Aggregate Formed from a Cationic Block Copolymer and Anionic Polysaccharide.

Block copolymers (PmMn; P20M101 and P100M98) comprising poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC, P) containing biocompatible phosphorylcholin pendants and cationic poly((3-acryloylaminopropyl) trimethylammonium chloride) (PMAPTAC, M) were synthesized via a controlled radical polymerization method. The degrees of polymerization of the PMPC and PMAPTAC segments are denoted by subscripts (PmMn). The mixture of cationic PmMn and anionic sodium chondroitin sulfate C (CS) with the pendant anionic carboxylate and sulfonate groups formed polyion complex (PIC) aggregates in phosphate-buffered saline. A charge-neutralized mixture of P20M101 with CS formed P20M101/CS PIC vesicles with a hydrodynamic radius (Rh) of 97.2 nm, zeta potential of ca. 0 mV, and aggregation number (Nagg) of 23,044. PMPC shells covered the surface of the PIC vesicles. The mixture of P100M98 and CS formed PIC spherical micelles with the PIC core and hydrophilic PMPC shells. The Rh, zeta potential, and Nagg of the PIC micelles were 26.4 nm, ca. 0 mV, and 404, respectively. At pH < 4, the carboxylate anions in CS were protonated. Thus, the charge balance in the PIC micelles shifted to decrease the core density owing to the electrostatic repulsions of the excess cations in the core. The PIC micelles dissociated at a NaCl concentration ≥0.6 M owing to the charge screening effect. The positively charged PIC micelles with excess P100M98 can encapsulate anionic dyes owing to electrostatic interaction.

Preparation of Water-Soluble Polyion Complex (PIC) Micelles with Random Copolymers Containing Pendant Quaternary Ammonium and Sulfonate Groups.

Cationic random copolymers (PCm) consisting of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC; P) with methacroylcholine chloride (MCC; C) and anionic random copolymers (PSn) consisting of MPC and potassium 3-(methacryloyloxy)propanesulfonate (MPS; S) were prepared via a reversible addition-fragmentation chain transfer method. "m" and "n" represent the compositions (mol %) of the MCC and MPS units in the copolymers, respectively. The degrees of polymerization for the copolymers were 93-99. Water-soluble MPC unit contains a pendant zwitterionic phosphorylcholine group whose charges are neutralized in pendant groups. MCC and MPS units contain the cationic quaternary ammonium and anionic sulfonate groups, respectively. The stoichiometrically charge-neutralized mixture of a matched pair of PCm and PSn aqueous solutions resulted in the spontaneous formation of water-soluble PCm/PSn polyion complex (PIC) micelles. These PIC micelles have the MPC-rich surface and MCC/MPS core. These PIC micelles were characterized using 1H NMR, dynamic and static light scattering, and transmission electron microscopic measurements. The hydrodynamic radius of these PIC micelles depends on the mixing ratio of the oppositely charged random copolymers. The charge-neutralized mixture formed maximum-size PIC micelles.

Comparison between Cashew-Based and Petrochemical Hydroxyoximes: Insights from Molecular Simulations.

Solvent extraction has been ubiquitously used to recover valuable metals from wastes such as spent batteries and electrical boards. With increasing demands for energy transition, there is a critical need to improve the recycling rate of critical metals, including copper. Therefore, the sustainability of reagents is critical for the overall sustainability of the process. Yet, the recycling process relies on functional organic compounds based on the hydroxyoxime group. To date, hydroxyoxime extractants have been produced from petrol-based chemical feedstocks. Recently, natural-based cardanol has been used to produce an alternative hydroxyoxime. The natural-based oxime has been employed to recover valuable metals (Ga, Ni, Co) via a liquid/liquid extraction process. The natural compound has a distinctive structure with 15 carbons in the alkyl tail. In contrast, petrol-based hydroxyoximes have only 12 or fewer carbons. However, the molecular advantages of this natural-based compound over the current petrol-based ones remain unclear. In this study, molecular dynamics simulation was employed to investigate the effect of extractant hydrocarbon chains on the extraction of copper ions. Two hydroxyoxime extractants with 12 and 15 carbons in the alkyl chain were found to have similar interactions with Cu2+ ions. Yet, a slight molecular binding increase was observed when the carbon chain was increased. In addition, lengthening the carbon chain made the extracting stage easier and the stripping stage harder. The binding would result in a lower pH in the extraction step and a lower pH in the stripping step. The insights from this molecular study would help design the extraction circuit using natural-based hydroxyoxime extractants. A successful application of cashew-based cardanol will improve the environmental benefits of the recycling process. With cashew-producing regions in developing countries, the application also improves these regions' social and economic sustainability.

Formation of Water-Soluble Complexes from Fullerene with Biocompatible Block Copolymers Bearing Pendant Glucose and Phosphorylcholine.

Double-hydrophilic diblock copolymers, PMPC100-block-PGEMAn (M100Gn), were synthesized via reversible addition-fragmentation chain transfer radical polymerization using glycosyloxyethyl methacrylate and 2-(methacryloyloxy)ethyl phosphorylcholine. The degree of polymerization (DP) of the poly(2-(methacryloyloxy) ethylphosphorylcholine) (PMPC) block was 100, whereas the DPs (n) of the poly(glycosyloxyethyl methacrylate) PGEMA block were 18, 48, and 90. Water-soluble complexes of C70/M100Gn and fullerene (C70) were prepared by grinding M100Gn and C70 powders in a mortar and adding phosphate-buffered saline (PBS) solution. PMPC can form a water-soluble complex with hydrophobic C70 using the same method. Therefore, the C70/M100Gn complexes have a core-shell micelle-like particle structure possessing a C70/PMPC core and PGEMA shells. The maximum amounts of solubilization of C70 in PBS solutions using 2 g/L each of M100G18, M100G48, and M100G90 were 0.518, 0.358, and 0.257 g/L, respectively. The hydrodynamic radius (Rh) of C70/M100Gn in PBS solutions was 55-75 nm. Spherical aggregates with a similar size to the Rh were observed by transmission electron microscopy. When the C70/M100Gn PBS solutions were irradiated with visible light, singlet oxygen was generated from C70 in the core. It is expected that the C70/M100Gn complexes can be applied to photosensitizers for photodynamic therapy treatments.

Preparation of Biocompatible Poly(2-(methacryloyloxy)ethyl phosphorylcholine) Hollow Particles Using Silica Particles as a Template.

Hydrophilic poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) shows biocompatibility because the pendant phosphorylcholine group has the same chemical structure as the hydrophilic part of phospholipids that form cell membranes. Hollow particles can be used in various fields, such as a carrier in drug delivery systems because they can encapsulate hydrophilic drugs. In this study, vinyl group-decorated silica particles with a radius of 150 nm were covered with cross-linked PMPC based on the graft-through method. The radius of PMPC-coated silica particles increased compared to that of the original silica particles. The PMPC-coated silica particles were immersed in a hydrogen fluoride aqueous solution to remove template silica particles to prepare the hollow particles. The PMPC hollow particles were characterized by dynamic light scattering, infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy observations. The thickness of the hollow particle shell can be controlled by the polymerization solvent quality. When a poor solvent for PMPC was used for the polymerization, PMPC hollow particles with thick shells can be obtained. The PMPC hollow particles can encapsulate hydrophilic guest molecules by immersing the hollow particles in a high-concentration guest molecule solution. The biocompatible PMPC hollow particles can be used in a drug carrier.

pH-Responsive Association Behavior of Biocompatible Random Copolymers Containing Pendent Phosphorylcholine and Fatty Acid.

Well-defined pH-responsive biocompatible random copolymers composed of 2-(methacryloyloxy)ethyl phosphorylcholine and varying quantities of sodium 11-(acrylamido)undecanoate (AaU) (fAaU = 0-58 mol %) were synthesized via reversible addition-fragmentation chain transfer radical polymerization. The pH-responsive association and dissociation behavior of the random copolymers was studied via turbidity, 1H nuclear magnetic resonance relaxation time, dynamic light scattering, static light scattering (SLS), and fluorescence measurements. At basic pH levels, the random copolymers dissolved in water in a unimer state because the AaU units behaved in a hydrophilic manner as a result of the ionization of the pendent fatty acids. The random copolymers with fAaU < 52 mol % associated intramolecularly within a single polymer chain to form unimer micelles at pH 3 because of the protonation of the pendent fatty acids. On the other hand, the random copolymer with fAaU ≥ 52 mol % formed intermolecular aggregates composed of four polymer chains at pH 3, as established by the SLS measurements. The random copolymers displayed the ability to solubilize hydrophobic guest molecules, such as N-phenyl-1-naphthylamine, into the hydrophobic microdomain formed by the pendent dehydrated fatty acids at acidic pHs. At pH 4, 1-pyrememethanol is captured by the random copolymer with fAaU = 52 mol %, and it is released from the random copolymer above pH 9. Furthermore, the mucoadhesive properties of the random copolymer with fAaU = 9 mol % were studied using a surface plasmon resonance technique. The copolymer was adsorbed onto mucin at pH 3; however, the adsorption decreased at pH 7.4.

"Foam Marble" Stabilized with One Type of Polymer Particle.

There has been increasing interest in colloidal particles adsorbed at the air-water interface, which lead to stabilization of aqueous foams and liquid marbles. The wettability of the particles at the interface is known to play an important role in determining the type of air/water dispersed system. Foams are preferably formed using relatively hydrophilic particles, and liquid marbles tend to be formed using relatively hydrophobic particles. In this study, submicrometer-sized polystyrene particles carrying poly(N,N-diethylaminoethyl methacrylate) hairs (PDEA-PS particles), which are synthesized by dispersion polymerization, are demonstrated to work as a particulate stabilizer for both aqueous foams and liquid marbles. A key point for the hydrophilic PDEA-PS particles to stabilize both aqueous foams and liquid marbles, which have been generally stabilized with hydrophilic and hydrophobic particles, respectively, is the wetting mode of the particles with respect to water. The flocculates of PDEA-PS particles adsorb to the air-water interface from the aqueous phase to stabilize foam in a Wenzel mode, and the dried PDEA-PS particles adsorb to the interface as aggregates from the air phase to stabilize liquid marbles in a metastable Cassie-Baxter mode. On the basis of the difference in the wetting mode, stabilization of an air-in-water-in-air multiple gas-liquid dispersed system, named "foam marble", is realized. After the evaporation of water from the foam marble, a porous sphere is successfully obtained with pore sizes of a few tens of micrometers (reflecting the bubble sizes) and a few tens of nanometers (reflecting the gap sizes among the PDEA-PS particles).

Reversal Activity and Toxicity of Heparin-Binding Copolymer after Subcutaneous Administration of Enoxaparin in Mice.

Uncontrolled bleeding after enoxaparin (ENX) is rare but may be life-threatening. The only registered antidote for ENX, protamine sulfate (PS), has 60% efficacy and can cause severe adverse side effects. We developed a diblock copolymer, heparin-binding copolymer (HBC), that reverses intravenously administered heparins. Here, we focused on the HBC inhibitory activity against subcutaneously administered ENX in healthy mice. BALB/c mice were subcutaneously injected with ENX at the dose of 5 mg/kg. After 110 min, vehicle, HBC (6.25 and 12.5 mg/kg), or PS (5 and 10 mg/kg) were administered into the tail vein. The blood was collected after 3, 10, 60, 120, 360, and 600 min after vehicle, HBC, or PS administration. The activities of antifactors Xa and IIa and biochemical parameters were measured. The main organs were collected for histological analysis. HBC at the lower dose reversed the effect of ENX on antifactor Xa activity for 10 min after antidote administration, whereas at the higher dose, HBC reversed the effect on antifactor Xa activity throughout the course of the experiment. Both doses of HBC completely reversed the effect of ENX on antifactor IIa activity. PS did not reverse antifactor Xa activity and partially reversed antifactor IIa activity. HBC modulated biochemical parameters. Histopathological analysis showed changes in the liver, lungs, and spleen of mice treated with HBC and in the lungs and heart of mice treated with PS. HBC administered in an appropriate dose might be an efficient substitute for PS to reverse significantly increased anticoagulant activity that may be connected with major bleeding in patients receiving ENX subcutaneously.

Heparin-Binding Copolymer as a Complete Antidote for Low-Molecular-Weight Heparins in Rats.

Bleeding resulting from the application of low-molecular-weight heparins (LMWHs) may be treated with protamine sulfate, but this treatment lacks efficiency; its action against antifactor Xa activity is limited to ∼60%. Moreover, protamine sulfate can cause life-threatening hypersensitivity reactions. We developed diblock heparin-binding copolymer (HBC), which can neutralize the anticoagulant activity of parenteral anticoagulants. In the present study, we explored the safety profile of HBC and its potential to reverse enoxaparin, nadroparin, dalteparin, and tinzaparin in human plasma and at in vivo conditions. HBC-LMWH complexes were characterized using zeta potential, isothermal titration calorimetry, and dynamic light scattering. The rat cardiomyocytes and human endothelial cells were used for the assessment of in vitro toxicity. Male Wistar rats were observed for up to 4 days after HBC administration for clinical evaluation, gross necropsy, and biochemistry and histopathological analysis. Rats were treated with LMWHs alone or followed by short-time intravenous infusion of HBC, and bleeding time and antifactor Xa activity were measured. HBC completely reversed antifactor Xa activity prolonged in vitro by all LMWHs with an optimal weight ratio of 2.5:1. The complexes of HBC-LMWHs were below 5 µm. We observed no effects on the viability of cardiovascular cells treated with HBC at concentrations up to 0.05 mg/ml. Single doses up to 20 mg/kg of HBC were well tolerated by rats. HBC completely reversed the effects of LMWHs on bleeding time and antifactor Xa activity in vivo after 20 minutes and retained ∼80% and ∼60% of reversal activity after 1 and 2 hours, respectively. Well-documented efficacy and safety of HBC both in vitro and in vivo make this polymer a promising candidate for LMWHs reversal. SIGNIFICANCE STATEMENT: Over the last decade, there has been significant progress in developing antidotes for the reversal of anticoagulants. Until now, there has been no effective and safe treatment for patients with severe bleeding under low-molecular-weight heparin therapy. Based on our in vitro and in vivo studies, heparin-binding copolymer seems to be a promising candidate for neutralizing all clinically relevant low-molecular-weight heparins.

Collapse Behavior of Polyion Complex (PIC) Micelles upon Salt Addition and Reforming Behavior by Dialysis and Its Temperature Responsivity.

Temperature-responsive polyion complex (PIC) micelles were prepared by using two diblock copolymers composed of a sulfobetaine chain (poly(sulfopropyldimethylammonium propylacrylamide), PSPP) and ionic chains (poly(sodium styrenesulfonate), PSSNa, or poly(3-(methacrylamido)propyltrimethylammonium chloride), PMAPTAC). Because the core is PIC and the shell is sulfobetaine with UCST-type temperature response, the corona expands and contracts in response to temperature. To control the size and uniformity of the PIC micelles, the collapse of PIC micelles by salt addition and the reforming behavior by dialysis were investigated by transmittance, DLS, TEM, AFM, and 1H NMR measurements. Investigation of the ionic species dependence of the added salt in the collapse behavior of PIC micelles revealed that it was dependent on the anionic species, although no dependence on the cationic species was observed. Its effectiveness was in the order of I- > Br- > Cl- > F-, which is in agreement with the order of ionic species with strong structural destruction in the Hofmeister series. Heterogeneous and large PIC micelles were formed by the simple mixing method. They collapsed by salt addition and were reformed by the dialysis method to form uniform and smaller PIC micelles. This is considered to be because a uniform and smaller micelle is formed to reform in equilibrium state by dialysis. The temperature response of PIC micelles formed by the simple mixing method and PIC micelles reformed by dialysis showed nearly the same temperature-transmittance curves. These results indicate that the temperature response of PIC micelles is affected by the concentration rather than the hydrodynamic radius. Furthermore, the stability of PIC micelles was found to be affected by the concentration temperature (the temperature at the time of concentration).

Polycation-Anionic Lipid Membrane Interactions.

Natural or synthetic polycations are used as biocides or as drug/gene carriers. Understanding the interactions between these macromolecules and cell membranes at the molecular level is therefore of great importance for the design of effective polymer biocides or biocompatible polycation-based delivery systems. Until now, details of the processes at the interface between polycations and biological systems have not been fully recognized. In this study, we consider the effect of strong polycations with quaternary ammonium groups on the properties of anionic lipid membranes that we use as a model system for protein-free cell membranes. For this purpose, we employed experimental measurements and atomic-scale molecular dynamics (MD) simulations. MD simulations reveal that the polycations are strongly hydrated in the aqueous phase and do not lose the water shell after adsorption at the bilayer surface. As a result of strong hydration, the polymer chains reside at the phospholipid headgroup and do not penetrate to the acyl chain region. The polycation adsorption involves the formation of anionic lipid-rich domains, and the density of anionic lipids in these domains depends on the length of the polycation chain. We observed the accumulation of anionic lipids only in the leaflet interacting with the polymer, which leads to the formation of compositionally asymmetric domains. Asymmetric adsorption of the polycation on only one leaflet of the anionic membrane strongly affects the membrane properties in the polycation-membrane contact areas: (i) anionic lipid accumulates in the region near the adsorbed polymer, (ii) acyl chain ordering and lipid packing are reduced, which results in a decrease in the thickness of the bilayer, and (iii) polycation-anionic membrane interactions are strongly influenced by the presence and concentration of salt. Our results provide an atomic-scale description of the interactions of polycations with anionic lipid bilayers and are fully supported by the experimental data. The outcomes are important for understanding the correlation of the structure of polycations with their activity on biomembranes.

CO2-Gas-Responsive Liquid Marble.

Liquid marbles were prepared using a water droplet and nonprotonated hydrophobic poly(2-N,N-diisopropylaminoethyl methacrylate) (PDiPAEMA) powder. Although the nonprotonated PDiPAEMA was hydrophobic, PDiPAEMA became hydrophilic because of the protonation of the pendant tertiary amino groups under acidic conditions. Therefore, liquid marbles stabilized with PDiPAEMA powder could float on a neutral to basic water surface, but they immediately disintegrated on an acidic water surface. Furthermore, the liquid marbles floating on the water surface disintegrated in response to CO2 gas because the water became acidic as a result of carbonic acid formation.

Adsorption Characteristics of Synthesized Polyelectrolytes onto Alumina Nanoparticles and their Application in Antibiotic Removal.

The present study aims to investigate the adsorption of synthesized poly(2-acrylamide-2-methylpropane sulfonic acid) (PAMPs) onto alumina nanoparticles and their application in the removal of ciprofloxacin (CFX) antibiotic from a water environment. The PAMPs were successfully synthesized and characterized by nuclear magnetic resonance and gel-permeation chromatography methods. The number- and weight-average molecular weights of PAMPs were 6.76 × 105 and 7.28 × 106 g/mol, respectively. The charge reversal of nanoalumina after PAMPs modification from positive to -37.5 mV was determined by ζ-potential measurement, while the appearance of C ═ O and N-H functional groups in PAMPs observed by Fourier-transform infrared spectroscopy confirmed them as the main indicators for adsorption of PAMPs onto a nanoalumina surface. The maximum adsorption capacity of PAMPs onto nanoalumina in 100 mg/L KCl was about 10 mg/g. The adsorption isotherms were fitted well by a two-step adsorption model. Application of PAMPs-modified nanoalumina (PAMNA) in CFX removal was also thoroughly studied. The optimum conditions for CFX removal using PAMNA were found to be pH 6, 10 mM NaCl, contact time 90 min, and adsorption dosage 5 mg/mL. The CFX adsorption isotherms and kinetics were in accordance with the two-step and pseudo-second-order models, respectively. The application for CFX removal in actual hospital wastewater was greater than 80%. The results of this study demonstrate that PAMNA is a new and promising material for antibiotic removal from wastewater.

Solution Properties of Amphoteric Random Copolymers Bearing Pendant Sulfonate and Quaternary Ammonium Groups with Controlled Structures.

Amphoteric random copolymers P(AMPS/APTAC50) x, where x = 41, 89, and 117, composed of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) and 3-acrylamidopropyltrimethylammonium chloride (APTAC) were prepared via reversible addition-fragmentation chain transfer radical polymerization. P(AMPS/APTAC50) x can dissolve in pure water to form small interpolymer aggregates. In aqueous solutions of NaCl, P(AMPS/APTAC50) x can dissolve in the unimer state. Amphoteric random copolymer P(AMPS/APTAC50)c with high molecular weight was prepared via conventional free-radical polymerization. Although P(AMPS/APTAC50)c cannot dissolve in pure water, it can dissolve in aqueous solutions of NaCl. In amphoteric random copolymers with high molecular weight, the possibility of continuous sequences of monomers with the same charge may increase, which may cause strong interactions between polymer chains. When fetal bovine serum (FBS) and polyelectrolytes were mixed in phosphate-buffered saline, the hydrodynamic radius and light-scattering intensity increased. There was no interaction between P(AMPS/APTAC50) x and FBS because corresponding increases could not be observed.

Thermo-Responsive Behavior of Amphoteric Diblock Copolymers Bearing Sulfonate and Quaternary Amino Pendant Groups.

Amphoteric diblock copolymers (S82A n) composed of poly(2-acrylamido-2-methylpropanesulfonic acid sodium salt) (PAMPS) with poly(3-(acrylamido)propyl trimethylammonium chloride) (PAPTAC) blocks were synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. Three S82A n were prepared with a fixed degree of polymerization (DP) for the PAMPS block (= 82) and different DP values for the PAPTAC blocks ( n = 37, 83, and 183). The solubility of S82A n was studied at different sodium chloride (NaCl) concentrations. S82A83 precipitated in pure water due to attractive electrostatic interactions with interpolymer chains. Conversely, S82A37 and S82A183 dissolved in pure water. In pure water S82A37 dissolved as a unimer state due to electrostatic repulsion of excess anionic charges in the polymer chain. The long anionic PAMPS block segment in S82A37 covered the short cationic PAPTAC block segment within a single polymer chain. In pure water S82A183 dispersed as polyion complex micelles due to electrostatic repulsion of the cationic PAPTAC shells. The oppositely charged PAMPS and PAPTAC blocks in S82A183 formed a core, while the excess PAPTAC block formed shells. S82A n showed lower critical solution temperature (LCST)-type thermo-responsive behavior at certain NaCl concentrations, and the LCST increased with the NaCl concentration. The mechanism of LCST behavior involves hydrogen bonding interactions between the pendant amide groups and water molecules.

Synthesis and Properties of Upper Critical Solution Temperature Responsive Nanogels.

A random copolymer ((U/A10)165) bearing pendent ureido groups and a small amount (10 mol %) of primary amino groups exhibits an upper critical solution temperature (UCST). We prepared a diblock copolymer (PMPC20P(U/A10)165) composed of water-soluble poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and (U/A10)165 blocks via reversible addition-fragmentation chain-transfer radical polymerization with postmodification reaction. The subnumbers are the degrees of polymerization of each block. Although in water PMPC20P(U/A10)165 dissolves as a unimer above the UCST phase transition temperature ( Tp), it forms polymer micelles composed of dehydrated (U/A10)165 cores and hydrophilic PMPC shells. A nanogel was prepared by cross-linking the pendent primary amines in the micelle core using (hydroxymethyl)phosphonium chloride below Tp. NMR and light-scattering data indicated that the nanogel core shrinks upon dehydration below Tp and swells upon hydration above Tp. The nanogel can encapsulate guest molecules such as hydrophobic fluorescence probes and bovine serum albumin (BSA) below Tp mainly owing to hydrophobic interactions in the core. Encapsulated BSA can be held in the nanogel core below Tp and subsequently released above Tp.

Temperature-Responsive Behavior of Double Hydrophilic Carboxy-Sulfobetaine Block Copolymers and Their Self-Assemblies in Water.

The block copolymer poly(2-((2-(methacryloyloxy)ethyl)dimethylammonio)acetate)- b-poly(3-( N-(2-metharyloylethyl)- N, N-dimethylammonio)propanesulfonate) (PGLBT- b-PSPE) was synthesized by reversible addition-fragmentation chain transfer (RAFT) technique under precise control. The PGLBT- b-PSPE block copolymers showed upper critical solution temperature (UCST) behavior originating from PSPE moieties. Unlike PSPE homopolymers, the transmittance change with temperature was gradual, and unexpected retardation or slight changes in a reverse direction were found at the intermediate stage. Light scattering and 1H NMR studies proved that the block copolymers formed spherical micelles that were composed of a PSPE core and PGLBT shell around room temperature and lower temperatures, and slowly disassociated with temperature increase. During the transition, fast (small particle) and slow (large particle) diffusive modes were detected by dynamic light scattering (DLS), which implied that the unimers were escaping from the self-assembled structure and swollen micelles, respectively. At sufficiently high temperatures where the solutions became almost transparent, the slow mode eventually disappeared, and only the fast mode remained. In addition, once the polymeric particles are formed, the size did not vary much with additional cooling. The transition point and the pattern of transmittance alteration were dependent on the degree of polymerization and the [PGLBT]:[PSPE] ratios; more PGLBT made the block copolymer less responsive to temperature and led the cloud point to lower degrees. However, random copolymers PGLBT- r-PSPE did not show any temperature-responsivity, and even small amount of GLBTs (10%) distributed in a PSPE chain significantly suppressed the transition.

Colloidal Stabilizer-Assisted Polymerization-Induced Precipitation Method for Colloidally Stable Polyacid Particles.

Near-monodispersed, colloidally stable, submicrometer-sized poly(acid phosphoxy ethyl methacrylate) (PAPEMA) latex particles were synthesized by free-radical dispersion polymerization using poly( N-vinylpyrrolidone) (PNVP) as both a steric colloidal stabilizer and a precipitating agent. Polymerization in the absence of PNVP led to a homogeneous transparent solution of PAPEMA, which indicates that the PNVP is essential for latex formation and the complex of PNVP and PAPEMA was formed during the dispersion polymerization. Dispersion copolymerizations with a divinyl cross-linking comonomer (∼20 wt % based on acid phosphoxy ethyl methacrylate) were also successful in synthesizing near-monodispersed, colloidally stable cross-linked PAPEMA latex particles, and the softness and p Ka values of the resulting PAPEMA latex particles can be controlled by varying the divinyl comonomer concentration. These sterically stabilized latex particles were characterized by electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, elemental microanalysis, and Fourier transform infrared spectroscopy. Characterization results indicated that the PNVP colloidal stabilizer was likely to be located homogeneously on the particle surfaces and within the interior of particles. Finally, it was demonstrated that the PAPEMA latex particles worked as an effective surface modifier for metal surfaces.