Temperature and pH sensitive ionic hydrogels based on new crosslinkers

New crosslinkers were synthesized from reaction of melamine with acryloyl and methacryloyl chloride in the presence of 1‐methyl‐2‐pyrrolidone as a solvent and triethyl amine as acid acceptor. The chemical structures of the prepared crosslinkers were elucidated from FT‐IR, ¹H‐NMR and ¹³C‐NMR analyses. Linear 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid and methacrylic acid (AMPS/MAA) copolymers were prepared and their viscometric properties in aqueous solution were investigated. Different weight percentages of the prepared crosslinkers were used as crosslinking agent (AMPS/MAA) to prepare ionic copolymers using ammonium persulfate as initiator. The percentage of crosslinkers was varied from 0.5 to 4 wt%. The swelling behaviors of crosslinked AMPS/MAA gels in deionized water were measured at different pH and temperatures. All AMPS/MAA copolymers exhibit faster deswelling rate at 50°C except for the copolymer containing 0.9 (mol ratio) AMPS. Copyright © 2005 John Wiley & Sons, Ltd.     

Aggregation behavior of amphiphilic random copolymer of 2‐(acrylamido)‐2‐methylpropanesulfonic acid and tris(trimethylsiloxy)silylpropylmethacrylate in aqueous solution

Aggregation behavior including dilute solution property and surface‐activity of the amphiphilic random copolymer composed of 2‐(acrylamido)‐2‐methylpropanesulfonic acid and tris(trimethylsiloxy)silylpropylmethacrylate (AMPS/TRIS copolymer) in aqueous solution were studied by static light scattering (SLS), dynamic light scattering (DLS), surface tension measurement, and transmission electron microscopy (TEM). The surface tension measurement made it clear that AMPS/TRIS copolymer exhibited weaker surface‐activity than a typical low‐molecular weight surfactant sodium dodecyl sulfate in water, that is, there were no plateau of surface tension γ versus concentration and no critical micelle concentration (CMC) in the whole concentration studied. SLS and DLS analyses, and TEM revealed that AMPS/TRIS copolymer self‐associated into imperfect core‐shell micelles having hydrophobic TRIS core surrounded by hydrophilic AMPS shell in water. AMPS shell was considered as a hard shell due to the stiffness of AMPS chain in water. TRIS chain could not densely aggregate in water due to the large steric hindrance between bulky trimethylsiloxy groups despite its hydrophobic nature, thereby providing TRIS core with less‐dense structure. The balance between the spreading force of stiff AMPS chain and the cohesion force of bulky TRIS chain provides the driving force for forming the unique micelle having less‐dense TRIS core and hard AMPS shell. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis and characterization of pH‐sensitive PAMPS/PVP nanogels in aqueous media

A novel method for preparing poly (2‐acrylamido‐2‐methylpropane sulfonic acid) (PAMPS) and poly (vinylpyrrolidone) (PVP) complex nanogels in PVP aqueous solution is discussed in this paper. The PAMPS/PVP complex nanogels were prepared via polymerization of 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) monomer in the presence of PVP nanoparticles which formed in water/acetone cosolvent in presence of N, N′‐methylenebisacrylamide (MBA) as a crosslinker, N, N, N′, N′‐tetramethylethylenediamine (TEMED) and potassium peroxydisulfate (KPS) as redox initiator system. The results of FTIR and ¹H NMR spectra indicated that the compositions of PAMPS/PVP are consistent with the designed structure. TEM micrographs proved that PAMPS/PVP nanogels possess the spherical morphology before and after swelling. These PAMPS/PVP nanogels exhibited pH‐induced phase transition due to protonation of PAMPS chains. The properties of PAMPS/PVP nanogels indicate that PAMPS/PVP nanogels can be developed into a pH‐controlled drug delivery system. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,characterization, and utilization of itaconate‐based polymerizable surfactants for the preparation of surface‐carboxylated polystyrene latexes

Two polymerizable surfactants (surfmers), namely, monododecyl itaconate (MDDI) and monocetyl itaconate (MCI), were synthesized by reacting itaconic anhydride with 1‐dodecanol and cetyl alcohol, respectively. A series of uncrosslinked and crosslinked surface‐carboxylated latexes were prepared from styrene and styrene–divinylbenzene, respectively, using varying amounts of these two surfmers. The latexes were characterized by gravimetry, dynamic light scattering, and conductometric titration in order to obtain the conversion, particle size distribution, and concentration of surface carboxyl groups, respectively. The size of latex varied between 41–72 nm and was seen to depend inversely on the surfmer concentration. In the case of the soluble polystyrene latexes, solution ¹H NMR spectra provided conclusive evidence for surfmer incorporation into the polymer chain. Comparison of the incorporation levels determined by NMR with the surface carboxylic acid concentrations in the latexes, determined by conductometric titrations, revealed that the majority of the surfmers, as ancticipated, were present on the latex surface. The study of the stability of the latexes to varying salt concentrations clearly demonstrated that the smaller‐size latexes having higher surface carboxyl group density exhibited far improved stability when compared with the larger‐size ones having lower surface carboxyl group density. Similarly, enhanced freeze‐thaw stability was also observed for the smaller‐size latexes. MCI‐based latexes exhibited marginally improved stability compared with those prepared using MDDI, which again seems to be because of the higher surface functional group density in the former. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3257–3267, 2005     

Reactive surfactants in heterophase polymerization: Colloidal properties,film‐water absorption,and surfactant exudation

In this article the results obtained with latexes prepared by emulsion polymerization with a conventional surfactant and a polymerizable surfactant (surfmer) are presented. For this study, well‐defined styrene‐butylacrylate latexes with a conventional nonreactive surfactant (sodium dodecyl sulfate) and a maleate diester surfmer, of which films can be easily cast, were used. The latex with the surfmer was prepared following a surfmer addition strategy to maximize the amount of surfmer bound to the particle surface, and not buried in the particle interior. The latex properties in terms of mechanical stability, film‐water absorption, and film‐surfactant exudation were assessed and compared. The mechanical stability and water‐absorption properties of the latex prepared with surfmer were better than those of the latex with sodium dodecyl sulfate. Additionally, by using a surfmer the surfactant migration to the film‐substrate and film‐air interfaces can be inhibited. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2994–3000, 2002     

Polymer coating of carboxylic acid functionalized multiwalled carbon nanotubes via reversible addition‐fragmentation chain transfer mediated emulsion polymerization

In this work, successful polymer coating of COOH‐functionalized multiwalled carbon nanotubes (MWCNTs) via reversible addition fragmentation chain transfer (RAFT) mediated emulsion polymerization is reported. The method used amphiphilic macro‐RAFT copolymers as stabilizers for MWCNT dispersions, followed by their subsequent coating with poly(methyl methacrylate‐co‐butyl acrylate). Poly(allylamine hydrochloride) was initially used to change the charge on the surface of the MWCNTs to facilitate adsorption of negatively charged macro‐RAFT copolymer onto their surface via electrostatic interactions. After polymerization, the resultant latex was found to contain uniform polymer‐coated MWCNTs where polymer layer thickness could be controlled by the amount of monomer fed into the reaction. The polymer‐coated MWCNTs were demonstrated to be dispersible in both polar and nonpolar solvents. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Interfacial crosslinking of self‐assembled triblock copolymer nanoparticles via alkoxysilane hydrolysis and condensation

The use of amphiphilic triblock copolymers bearing a reactive alkoxysilane middle block as polymeric stabilizers is reported in this work. A series of poly(ethylene glycol) methyl ether methacrylate‐b‐(3‐trimethoxysilyl)propyl methacrylate‐b‐benzyl methacrylate (PEGMA‐b‐MPS‐b‐BzMA) triblock copolymers were prepared by RAFT solution polymerization and polymerization‐induced self‐assembly (PISA), respectively, where the various block lengths and overall composition were varied. The copolymers prepared by solution polymerization were employed as oil‐in‐water stabilizers where upon application of a catalyst, the 3‐(trimethoxysilyl)propyl methacrylate (MPS) block at the droplet interface was crosslinked to yield capsule‐like structures. The effectiveness of interfacial crosslinking was validated by dynamic light scattering and electron microscopy. In situ self‐assembly by the PISA method resulted in spherical nanoparticles of controllable size that were readily crosslinked by addition of base, with significant enhancement of colloidal stability. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1897–1907     

Preparation of micron-size monodisperse poly(2-hydroxyethyl methacrylate) particles by dispersion polymerization

Dispersion polymerization of 2-hydroxyethyl methacrylate using four categories of polymeric stabilizers in a mixture of good and poor solvents was performed to produce polymeric particles. The stabilizers employed were methyl methacrylate and styrene homopolymers, methacryloyl-terminated poly(methyl methacrylate) and polystyrene macromonomers, an amphiphilic poly(methyl methacrylate-co-methacrylic acid-graft-styrene), and polybutadiene derivatives containing reactive vinyl groups. Dispersion copolymerization with a small amount of the macromonomer gave micron-size particles with relatively narrow size distribution. The amphiphilic graft copolymer and the polybutadiene derivatives also afforded monodisperse particles. The mixed ratio between good and poor solvents greatly affected the particle size and size distribution. © 1996 John Wiley & Sons, Inc.     

Emulsion procedures for thermally reversible covalent crosslinking of polymers

Quaternization and dequaternization of tertiary amine compounds were employed to obtain thermally reversible ionene networks from aqueous colloidal polymer dispersions prepared via emulsion polymerization. Chlorine‐functionalized polymers prepared via the emulsion copolymerization of styrene (St), butylacrylate (BA), or both with chloromethylstyrene, and amino‐functionalized polymers prepared via the emulsion copolymerization of St, BA, or both with 2‐(dimethylamino)ethylacrylate or 4‐vinylpyridine, were reacted without polymer separation, with a ditertiaryamine crosslinker and a dihalide crosslinker, respectively, to obtain crosslinked polymers. Crosslinked polymers were also obtained via the reaction of a chlorine‐functionalized polymer dispersion with an amino‐functionalized polymer dispersion or via the drying of the polymer blend prepared from the two kinds of dispersions. Reactive solubility experiments, flowability investigations (by thermocompression at ca. 215 °C), IR, and ¹H NMR analyses of the obtained crosslinked polymers indicated that the generated ionene bridges dequaternized on heating and requaternized on cooling. In comparison with solution crosslinking, no organic solvent was employed, and simple procedures were required for the preparation of the thermally reversible covalent crosslinked polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4373–4384, 2000     

Tuning amphiphilicity/temperature‐induced self‐assembly and in‐situ disulfide crosslinking of reduction‐responsive block copolymers

New poly(ethylene oxide)‐based block copolymers (ssBCs) with a random copolymer block consisting of a reduction‐responsive disulfide‐labeled methacrylate (HMssEt) and a thermoresponsive di(ethylene glycol)‐containing methacrylate (MEO₂MA) units were synthesized. The ratio of HMssEt/MEO₂MA units in the random P(MEO₂MA‐co‐HMssEt) copolymer block enables the characteristics of well‐defined ssBCs to be amphiphilic or thermoresponsive and double hydrophilic. Their amphiphilicity or temperature‐induced self‐assembly results in nanoaggregates with hydrophobic cores having different densities of pendant disulfide linkages. The effect of disulfide crosslinking density on morphological variation of disulfide‐crosslinked nanogels is investigated. In response to reductive reactions, the partial cleavage of pendant disulfide linkages in the hydrophobic cores converts the physically associated aggregates to disulfide‐crosslinked nanogels. The occurrence of in‐situ disulfide crosslinks provides colloidal stability upon dilution. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2057–2067     

Highly Efficient Synthesis and Assay of Protein‐Imprinted Nanogels by Using Magnetic Templates

We report an approach integrating the synthesis of protein‐imprinted nanogels (“plastic antibodies”) with a highly sensitive assay employing templates attached to magnetic carriers. The enzymes trypsin and pepsin were immobilized on amino‐functionalized solgel‐coated magnetic nanoparticles (magNPs). Lightly crosslinked fluorescently doped polyacrylamide nanogels were subsequently produced by high‐dilution polymerization of monomers in the presence of the magNPs. The nanogels were characterised by a novel competitive fluorescence assay employing identical protein‐conjugated nanoparticles as ligands to reversibly immobilize the corresponding nanogels. Both nanogels exhibited K_d<10 pM for their respective target protein and low cross‐reactivity with five reference proteins. This agrees with affinities reported for solid‐phase‐synthesized nanogels prepared using low‐surface‐area glass‐bead supports. This approach simplifies the development and production of plastic antibodies and offers direct access to a practical bioassay.     

Effect of sulfonated 3-pentadecyl phenyl acrylate as surfmer in the emulsion polymerization of styrene: synthesis and polymer properties

In this work, the evaluation of a newly developed anionic polymerizable surfactant (surfmer), viz., sulfonated 3-pentadecyl phenyl acrylate, in the emulsion polymerization of styrene and its effect on the polymer properties is reported. The results were compared with the commercially available non-reactive anionic surfactant sodium lauryl sulfate. The surfmer has a low critical micellar concentration value of 40.11 mg/L (8.7?×?10^?5?mol/L) in comparison to 2,400 mg/L (8.28?×?10^?3?mol/L) for sodium dodecyl sulfate. Nanosized polystyrene dispersions with varying concentration of this surfmer were prepared and characterized for conversion, particle size, and size distribution at a fixed monomer/water ratio of 0.1. The particle radii decreased from 560 nm for the surfactant-free dispersions to 45 nm for the dispersion with 2.3 mol% surfmer. Increasing surfmer content above this concentration did not further affect the particle size but increased the width of the particle size distribution. Transmission electron microscopy results along with particle size data show that with increasing surfmer content the particle size distribution broadens, and film formation is facilitated. The microstructure analysis of the copolymers using infrared and ¹H-NMR spectroscopy confirms that the surfmer is chemically attached to the polymer chains. The effect of the ionic sulfonate groups and the alkyl chains of the surfmer moieties on the polymer properties have been studied through measurement of dilute solution viscosity and thermal and viscoelastic properties. These results indicate that the behavior of surfmer-containing polymers resembles that of plasticized ionomers.     

Facile Synthesis of Resveratrol Nanogels with Enhanced Fluorescent Emission

Herein, a kind of fluorescent resveratrol nanogels via one‐pot thiol‐ene Michael addition polymerization of resveratrol triacrylate, 1,6‐hexanedithiol, and methoxyl poly(ethylene glycol) acrylate is prepared. The resultant nanogels can be well‐dispersed in water with a hydrodynamic radius of around 68 nm, and the nanogels are stable in both water and organic solvents. Moreover, the resveratrol nanogels exhibit elevated fluorescence intensity compared to free resveratrol, and the quantum yield of resveratrol nanogels is estimated to be 5.8 times as that of free resveratrol dispersed in water. Fluorescence image results also demonstrate that the resveratrol nanogels can be used for cell imaging in MCF‐7 human breast cancer cells. Therefore, the resveratrol nanogels are expected to be used as a trackable drug delivery system.     

Core–shell nanogels by RAFT crosslinking polymerization: Synthesis and characterization

A synthetic methodology is described for the preparation of core–shell nanogels by reversible addition‐fragmentation chain transfer. Well‐defined macro chain transfer agents (macro‐CTA's) were prepared in a first step using monomers that yield sensitive polymers. In the second step, a crosslinker alone or with the addition of a functionalized comonomer were used to form a crosslinked core. The ratio of crosslinker to macro‐CTA is crucial to yield nanogels. Furthermore, the polymerization time has an impact in the architecture of the nanomaterial obtained: it evolves from a core‐crosslinked star to a core–shell nanogel. Controlling the molecular weight of the macro‐CTA and the type of comonomer in the core forming step, core–shell nanogels with hydrodynamic diameters from 22 to 168 nm and a core that represents from 35 to 77% of the size, were prepared containing functional groups in the core which could be used as catalytic scaffolds. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

Preparation of initiator and cross-linker-free poly(N-isopropylacrylamide) nanogels by photopolymerization

Poly(N-isopropylacrylamide) or PNIPAm nanogels with diameter of 50–200 nm were prepared from N-isopropylacrylamide monomer by photopolymerization in the absence of initiator, cross-linker and surfactant. Morphology transition of the nanogels from branch to compact, global one was tuned with NIPAm(N-isopropylacrylamide) concentration in reaction. Reaction mechanism of the nanogels formation was proposed. The yield of prepared nanogels can increased from ca. 20 up to 86% when solution pH varied from neutral to 2. ESR signals confirmed that the existence of H⁺ in reaction could accelerate the polymerization of NIPAm.     

Pickering Interfacial Catalysis for Biphasic Systems: From Emulsion Design to Green Reactions

Pickering emulsions are surfactant‐free dispersions of two immiscible fluids that are kinetically stabilized by colloidal particles. For ecological reasons, these systems have undergone a resurgence of interest to mitigate the use of synthetic surfactants and solvents. Moreover, the use of colloidal particles as stabilizers provides emulsions with original properties compared to surfactant‐stabilized emulsions, microemulsions, and micellar systems. Despite these specific advantages, the application of Pickering emulsions to catalysis has been rarely explored. This Minireview describes very recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions with special emphasis on their assets and challenges for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.     

Polymer nanoparticles with a sensitive CO2‐responsive hydrophilic/hydrophobic surface

Poly(methyl methacrylate) (PMMA) nanoparticles with a sensitive CO₂‐responsive hydrophilic/hydrophobic surface that confers controlled dispersion and aggregation in water were prepared by emulsion polymerization at 50 °C under CO₂ bubbling using amphiphilic diblock copolymers of 2‐dimethylaminoethyl methacrylate (DMAEMA) and N‐isopropyl acrylamide (NIPAAm) as an emulsifier. The amphiphilicity of the hydrophobic–hydrophilic diblock copolymer at 50 °C was triggered by CO₂ bubbling in water and enabled the copolymer to serve as an emulsifier. The resulting PMMA nanoparticles were spherical, approximately 100 nm in diameter and exhibited sensitive CO₂/N₂‐responsive dispersion/aggregation in water. Using copolymers with a longer PNIPAAm block length as an emulsifier resulted in smaller particles. A higher concentration of copolymer emulsifier led to particles with a stickier surface. Given its simple preparation and reversible CO₂‐triggered amphiphilic behavior, this newly developed block copolymer emulsifier offers a highly efficient route toward the fabrication of sensitive CO₂‐stimuli responsive polymeric nanoparticle dispersions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2149–2156     

Investigation of the influence of the architectures of poly(vinyl pyrrolidone) polymers made via the reversible addition–fragmentation chain transfer/macromolecular design via the interchange of xanthates mechanism on the stabilization of suspension polymerizations

Linear, star, and block copolymers based on poly(vinyl pyrrolidone) (PVP) were synthesized with the macromolecular design via the interchange of xanthates (MADIX) process for use as potential stabilizers in suspension polymerization. The design of the leaving group of the dithioxanthate‐based transfer agent was shown to be key to the successful preparation of well‐defined PVP architectures. A linear correlation of the monomer conversion and molecular weight was found in the synthesis of star polymers, whereas the molecular weight distribution remained narrow (polydispersity index < 1.3). Significant side reactions, which typically broaden the molecular weight distribution when R‐designed MADIX agents are used, were absent. The living behavior of the PVP polymerization was furthermore confirmed via chain extension with vinyl acetate, which resulted in the formation of PVP–PVAc block copolymers [where PVAc is poly(vinyl acetate)]. The prepared polymers were used as stabilizers in suspension polymerization to prepare crosslinked poly(vinyl neodecanoate)/ethylene glycol dimethacrylate microspheres. The ratio of the interfacial tension of the aqueous and monomer phases and the overall viscosity were found to have an effect on the diameter of the particles, with PVP star polymers as stabilizers resulting in smaller particles. A smaller interfacial tension, measured when star polymers and block copolymers were used, resulted in the appearance of smaller particles, probably because of more breakup events of the monomer droplets and the enhanced stabilization of the particle surface area. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4372–4383, 2006     

Synthesis of biocompatible and thermally sensitive poly(N‐vinylcaprolactam) nanogels via inverse miniemulsion polymerization: Effect of the surfactant concentration

The goal of this study was to develop a new route to prepare thermally responsive polymer nanogels. Poly(N‐vinylcaprolactam) nanogels were prepared via inverse miniemulsion polymerization (W/O) at 70 °C using n‐hexadecane as a nonpolar continuous phase, potassium persulfate as an initiator, and N,N′‐methylenebisacrylamide as a crosslinker. Sorbitan monooleate (Span 80) was used as surfactant and its influence on the polymerization kinetics and on the colloidal characteristics of the nanogels were principally investigated. It was observed that the addition of a strong “lipophobe” is required to stabilize the resulting miniemulsion. The nanogels were characterized in terms of morphology, size, zeta potential, and thermoproperties using transmission electron microscopy and dynamic light scattering. It was observed that all the nanogels obtained collapsed when the lower critical solution temperature (LCST) was raised. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3932–3941, 2010     

Synthesis of surfactant‐free carbon nanotube/poly(styrene‐co‐acrylamide) by dynamic interfacial emulsion polymerization under sonication

This paper describes a study on emulsifier‐free ultrasonically assisted in‐situ copolymerization method of acrylamide and styrene in the presence of CNT, resulting in stable and uniform dispersions. The dispersions prepared were found stable for several months. Thermogravimetric analysis (TGA) curves and conversion measurements provided an insight regarding the polymerization mechanism and the nanocomposites structure. Films prepared of the polymerization products resulted in some clear and transparent coatings. The polymerization method described is simple and very fast compared with the other literature reported methods. TGA was extensively used as an analytical tool for determination of the composition of acrylamide–styrene copolymers. TGA and differential scanning calorimetry indicate that the polymerization product is largely a poly(styrene‐co‐acrylamide), where the acrylamide fraction is attached to the CNT surfaces. The copolymer produced, with and without CNT, is essentially a block copolymer, where each block contains small amounts of the other comonomer. To the authors' best knowledge, this report is the first one describing the production of stable dispersions of CNT in surfactant‐free poly(styrene‐co‐acrylamide) emulsion. Copyright © 2013 John Wiley & Sons, Ltd.