Synthesis and swelling properties of a pH‐ and temperature‐dual responsive hydrogel by inverse microemulsion polymerization

A novel pH‐ and temperature‐dual responsive hydrogel was synthesized by inverse microemulsion polymerization, using itonic acid (IA) as pH‐responsive monomer, N‐isopropylacrylamide (NPAM) as thermo‐responsive monomer and acrylamide (AM) as the nonionic hydrophilic monomer. Factors affecting water and salt absorption, as well as swellability of the dual responsive hydrogels, such as IA/NPAM mass ratio and crosslinker amount, were investigated. pH‐ and temperature‐sensitivity and dynamic viscoelasticity behaviors of the dual responsive hydrogels were also studied. The dual responsive responsive hydrogels showed suitable water and salt absorbency, remarkable pH‐, and temperature‐sensitivity, adjustable swellability and enhanced viscoelastic behaviors under high stress. Water absorbency and pH‐sensitivity increased while salt absorbency and temperature‐ sensitivity decreased with increasing IA/NIPAM mass ratio. Both water absorbency and salt absorbency increased first with crosslinker amount increased to 0.2 wt %, and then decreased with increasing crosslinker amount. Temperature‐induced shrinkage range of the dual responsive hydrogels was higher and broader than that of the conventional poly(N‐isopropylacrylamide) hydrogel. TEM indicated that the as‐synthesized hydrogel particles were regular and spherical‐like in shape and had the mean particle size of 49nm in the range of 30–78 nm. FTIR indicated the structure of the dual responsive hydrogels. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42139.     

Poly(ε‐caprolactone)‐graft‐poly(N‐isopropylacrylamide) amphiphilic copolymers prepared by a combination of ring‐opening polymerization and atom transfer radical polymerization: Synthesis,self‐assembly,and thermoresponsive property

Thermoresponsive graft copolymers of ε‐caprolactone and N‐isopropylacrylamide were synthesized by a combination of ring‐opening polymerization and the sequential atom transfer radical polymerization (ATRP). The copolymer composition, chemical structure, and the self‐assembled structure were characterized. The graft length and density of the copolymers were well controlled by varying the feed ratio of monomer to initiator and the fraction of chlorides along PCL backbone, which is acting as the macroinitiator for ATRP. In aqueous solution, PCL‐g‐PNIPAAm can assemble into the spherical micelles which comprise of the biodegradable hydrophobic PCL core and thermoresponsive hydrophilic PNIPAAm corona. The critical micelle concentrations of PCL‐g‐PNIPAAm were determined under the range of 6.4–23.4 mg/L, which increases with the PNIPAAm content increasing. The mean hydrodynamic diameters of PCL‐g‐PNIPAAm micelles depend strongly on the graft length and density of the PNIPAAm segment, allowing to tune the particle size within a wide range. Additionally, the PCL‐g‐PNIPAAm micelles exhibit thermosensitive properties and aggregate when the temperature is above the lower critical solution temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41115.     

Synthesis of well‐defined,functionalized polymer latex particles through semicontinuous emulsion polymerization processes

The design of a semicontinuous emulsion polymerization process, primarily based on theoretical calculations, has been carried out with the objective of achieving overall independent control over the latex particle size, the monodispersity in the particle size distribution, the homogeneous copolymer composition, the concentration of functional groups (e.g., carboxyl groups), and the glass‐transition temperature with n‐butyl methacrylate/n‐butyl acrylate/methacrylic acid as a model system. The surfactant coverage on the latex particles is very important for maintaining a constant particle number throughout the feed process, and this results in the formation of monodisperse latex particles. A model has been set up to calculate the surfactant coverage from the monomer feed rate, surfactant feed rate, desired solid content, and particle size. This model also leads to an equation correlating the polymerization rate to the instantaneous conversion of the monomer or comonomer mixture. This equation can be used to determine the maximum polymerization rate, only below or at which monomer‐starved conditions can be achieved. The maximum polymerization rate provides guidance for selecting the monomer feed rate in the semicontinuous emulsion polymerization process. The glass‐transition temperature of the resulting carboxylated poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) copolymer can be adjusted through variations in the compositions of the copolymers with the linear Pochan equation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 30–41, 2003     

Polymer–metal composite particles: Metal particles on poly(St‐co‐MAA) microspheres

Poly(styrene‐co‐methacrylic acid) P(St‐co‐MAA) microspheres with a monodisperse size distribution were prepared by emulsifier‐free emulsion copolymerization of St and MAA. The effects of MAA content on the polymerization rate and the content of MAA in the copolymer were investigated by gravimetrical and IR methods, respectively. The results of XPS measurement indicated the presence of a carboxyl functional group. By chemical metal deposition, nickel or palladium particles were formed and deposited on the surface of P(St‐co‐MAA) microspheres to form P(St‐co‐MAA)Ni or P(St‐co‐MAA)Pd composite particles. XRD measurement and TEM observation confirmed that nickel and palladium metal particles in a small size (20–40 nm) were distributed on surface of the copolymer microspheres. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1693–1698, 2000     

Photo/pH dual‐responsive biocompatible poly(methacrylic acid)‐based particles for triggered drug delivery

A novel dual‐responsive (light and pH) particle based on poly(methacrylic acid), poly(methacrylic acid)–poly[1‐(2‐nitrophenyl)ethane‐1,2‐diyl bis(2‐methylacrylate)]was prepared with the facile method of two‐step homogeneous radical polymerization with methacrylic acid as the monomer and 1‐(2‐nitrophenyl)ethane‐1,2‐diyl bis(2‐methylacrylate) as a photodegradable crosslinker. Photolytic assessments were conducted upon irradiation with a UV lamp; this led to particle disintegration caused by cleavage of the photolabile crosslinking points. The light‐dependent degradation was investigated through particle size changes, absorption spectra variations, surface morphology changes, Fourier transform infrared spectroscopy, and the release of Nile red from the particles after irradiation. The pH dependence of the particle systems induced by the protonation and deprotonation of poly(methacrylic acid) was also confirmed by fluorescence spectroscopy. The triggered release of fluorescein diacetate was investigated to demonstrate that the release behavior in cells was light dependent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44003.     

Adsorption of Cu2+ ions with poly(N‐isopropylacrylamide‐co‐methacrylic acid) micro/nanoparticles

Chelation efficiency of stimuli‐responsive poly(N‐iospropylacrylamide‐co‐methyacrylic acid) (PNIPAAm‐MAA) nanoparticles with Cu²⁺ ions from CuSO₄·5H₂O solution and from wood treated with copper‐based preservatives was studied. It was shown that particle size played a very important role in the adsorption process. The nano‐scale particles showed much improved Cu ion adsorption efficiency, compared with the micro hydrogels. The amount of Cu ion adsorption increased with increase of MAA ratio in copolymers and adsorption efficiency decreased with increased particle size. Furthermore, the adsorption amount varied with adsorption temperature at temperatures both below and above the corresponding low critical solution temperature (LCST). The high adsorption efficiency of Cu ions by PNIPAAm‐MAA polymer particles provides an effective technique for recovering metal ions (e.g., Cu²⁺) from wood treated with metal‐based preservatives. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of nanometer‐sized poly(methacrylic acid) particles in water‐in‐oil microemulsions

A water‐in‐oil microemulsion, water‐in‐cyclohexane stabilized by poly(ethylene glycol) tert‐octylphenyl, was developed to prepare poly(methacrylic acid) (PMAA) particles. Up to 100% conversion of the amphiphilic monomer, methacrylic acid (MAA), which could not be converted to the polymer efficiently in a dioctylsulfosuccinate sodium salt/toluene microemulsion, was achieved. The viscosity‐average molecular weight of the PMAA prepared was 1.45 × 10⁵ g/mol. The effects of some polymerization parameters, including the reaction temperature and the concentrations of the initiator and the monomer, on the polymerization of MAA were investigated. The results showed that the polymerization rate of MAA was slower than that of acrylamide in the microemulsions reported in the literature. The degree of conversion increased with the initiator concentration, reaction temperature, and monomer concentration. However, the stable microemulsions became turbid during the polymerization when the reaction temperature was at 70°C or at a high monomer concentration (40 wt %) The synthesized PMAA particles were spherical and had diameters in the range of ～50 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2497–2503, 2006     

Preparation,characterization, and drug‐release properties of poly(N‐isopropylacrylamide) microspheres having poly(itaconic acid) graft chains

An inverse suspension polymerization method for the preparation of thermoresponsive hydrogel microspheres based on N‐isopropylacrylamide was described in this article. The polymerization reaction was carried out at 200 rpm stirring rate and the microspheres obtained were in the size range of 71–500 μm in the swollen states. The particles were sieved by using ASTM sieves. The selected fraction (180–250 μm) of poly(N‐isopropylacrylamide) (PNIPAAm) microspheres was used for radiation‐induced modification with itaconic acid (IA) to obtain PNIPAAm/poly(itaconic acid) graft copolymer. Viagra and lidocaine were used as model drugs for the investigation of controlled‐release behavior of the microspheres. Incorporation of IA graft chains onto microspheres enhanced significantly the uptake of both drugs and further controlled release at specific pH values. The release studies showed that some of the basic parameters affecting the drug‐loading and ‐release behavior of the microspheres were pH, temperature, particle size, and chemical nature of drug. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1115–1124, 2005     

Modeling diameter distributions of poly(N‐isopropylacrylamide‐co‐methacrylic acid) nanoparticles

The Weibull distribution was successfully used to describe the diameter distribution of poly(N‐isopropylacrylamide‐co‐methacrylic Acid (PNIPAAm‐MAA) nanoparticles, whereas the lognormal was deemed not adequate for that purpose. The method of moments was used to predict parameters of the Weibull distribution. In this approach, the Weibull parameters were recovered from the diameter mean and variance, both of which were predicted from temperature. The distributions predicted from various temperatures for both MAA/NIPAAm ratios of 0.05 and 0.10 showed trends similar to those displayed in the observed data. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

pH‐responsive permeability of PE‐g‐PMAA membranes

Poly(methacrylic acid) (PMAA) grafted porous PE membranes (PE‐g‐PMAA) were studied. It was found that (1) a wide range of graft yields can be achieved by varying irradiation time (20–240 min) and monomer concentration (0.22M–0.66M), (2) the grafted membrane exhibits reversible permeability response, (3) the membrane shows a maximum permeability response at an intermediate permeant molecular weight due to size exclusion effect, and (4) depending on the graft yield, two types of permeability response can be obtained. These observations are consistent with our earlier study on poly(N‐isopropylacrylamide) (PNIPAAm)–grafted porous polyethylene membranes. In addition, it was observed that the solvent used during grafting may influence the graft location—presumably due to variations in pore wetting. Specifically, compared to water solvent, methanol can increase grafting inside membrane pores, an observation inferred from membrane swelling, thickness measurement, and SEM characterization. Moreover, preferential grafting inside the membrane pores, as affected by increasing methanol content in the grafting solvent, results in lower membrane permeability and a greater pore graft‐controlled type of permeability response. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 778–786, 2000     

Sorption and desorption properties of random copolymer hydrogels of N‐isopropylacrylamide and N‐ethylacrylamide: Effect of monomer composition

Random copolymer hydrogels of N‐isopropylacrylamide and N‐ethylacrylamide (NEAM) were prepared using different monomer compositions in 1:1 methanol–water mixtures. The samples were characterized by cononsolvency study in methanol‐water mixtures at various temperatures, swelling properties measurements, scanning electron microscopy. With changing ratio of the monomers in the reaction mixture, the thermal, morphological and swelling properties, varied significantly. The change in the properties with monomer composition variation are interpreted based on the different thermoresponsive characteristics and interactions of gels of N‐isopropylacrylamide and NEAM (homo‐ and copolymer gels) in water and different methanol‐water mixtures, their variable compositions in the synthesis mixtures, and their morphologies. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45176.     

Uniform star‐polystyrene nanoparticles prepared by emulsion atom transfer radical polymerization

Pentaerythritol (PT) was converted into four‐arm initiator pentaerythritol tetrakis(2‐chloropropionyl) (PT‐Cl) via reaction with 2‐chloropropionyl chloride. Uniform (monodisperse) star‐polystyrene nanoparticles were prepared by emulsion atom transfer radical polymerization of styrene, using PT‐Cl/CuCl/bpy (bpy is 2,2′‐dipyridyl) as the initiating system. The structures of PT‐Cl and polymer were characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. The morphology, size and size distribution of the star‐polystyrene nanoparticles were characterized by transmission electron microscopy, atomic force microscopy and photon correlation spectroscopy. It was found that the average diameters of star‐polystyrene nanoparticles were smaller than 100 nm (30–90 nm) and monodisperse; moreover, the particle size could be controlled by the monomer/initiator ratio and the surfactant concentration. The average hydrodynamic diameter (D_h) of the nanoparticles increased gradually on increasing the ratio of styrene to PT‐Cl and decreased on enhancing the surfactant concentration or increasing the catalyst concentration. Copyright © 2011 Society of Chemical Industry     

Preparation and characterization of core‐shell nanoparticles containing poly(chlorotrifluoroethylene‐co‐ethylvinylether) as core

Core shell latex particles with a glassy core and a low T_g polymeric shell are usually preferred. More so, the glassy core happens to be a fluoropolymer with a shell polymer that helps in processability. We describe here the preparation and characterization of core shell nanoparticles consisting of poly(chlorotrifluoroethylene‐co‐ethylvinylether) as core encapsulated in poly(styrene‐acrylate) copolymer shell using seeded emulsion polymerization method under kinetically controlled monomer starved conditions. Properties of the emulsion using surfactants (fluoro/conventional) and surfactant free conditions were investigated. Average size (100 nm), spherical shape and core–shell morphology of the latex particles was confirmed by dynamic light scattering and transmission electron microscopy. Absence of C? F and C? Cl peaks in X‐ray photoelectron spectroscopy proves that cores are completely covered. Polymerization in the presence of fluorocarbon surfactant was found to give optimum features like narrow size distribution, good shell deposition and no traces of agglomeration. Films of core shell latex particles exhibited improved transparency and enhanced water contact angles thus making them suitable for applications in various fields including coatings. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

pH and thermo‐responsive poly(N‐isopropylacrylamide) copolymer grafted to poly(ethylene glycol)

pH and thermo‐responsive graft copolymers are reported where thermo‐responsive poly(N‐isopropylacrylamide) [poly(NIPAAm), poly A ], poly(N‐isopropylacrylamide‐co‐2‐(diethylamino) ethyl methacrylate) [poly(NIPAAm‐co‐DEA), poly B ], and poly(N‐isopropylacrylamide‐co‐methacrylic acid) [poly(NIPAAm‐co‐MAA), poly C ] have been installed to benzaldehyde grafted polyethylene glycol (PEG) back bone following introducing a pH responsive benzoic‐imine bond. All the prepared graft copolymers for PEG‐g‐poly(NIPAAm) [ P‐N1 ], PEG‐g‐poly(NIPAAm‐co‐DEA) [ P‐N2 ], and PEG‐g‐poly(NIPAAm‐co‐MAA) [ P‐N3 ] were characterized by ¹H‐NMR to assure the successful synthesis of the expected polymers. Molecular weight of all synthesized polymers was evaluated following gel permeation chromatography. The lower critical solution temperature of graft copolymers varied significantly when grafted to benzaldehyde containing PEG and after further functionalization of copolymer based poly(NIPAAm). The contact angle experiment showed the changes in hydrophilic/hydrophobic behavior when the polymers were exposed to different pH and temperature. Particle size measurement investigation by dynamic light scattering was performed to rectify thermo and pH responsiveness of all prepared polymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Temperature and pH‐Dependent Swelling Behavior of Poly(N‐isopropylacrylamide) Copolymer Hydrogels and Their Use in Flow Control

Poly(N‐isopropylacrylamide) (PNIPAAm) copolymer gels with acidic and basic comonomers of various molar ratios were prepared by radical polymerization. The relationship between the swelling behavior of the gels and the copolymerization ratio was studied experimentally at different temperatures and in various pH value buffer solutions. The results of the experiments revealed that the transition temperatures of the PNIPAAm copolymer gels were changed in proportion to the monomer ratio used in copolymerization. The pH value of the buffer solution strongly affected the swelling ratio and some of the transition temperatures of the gels. The PNIPAAm copolymer gels were used in a chemo‐mechanical valve. The liquid flows directly through a gel actuator, which consists of a cylindrical actuator chamber filled with small particles of the sensitive cross‐linked polymer. The flow rate as well as the pressure drop was measured in dependence on the solvent properties. With the presented experimental arrangement it could be shown that sensitive polymers can be used for controlling the flow in dependence on temperature and pH.

pH‐Dependence of the pressure in a chemo‐mechanical valve.     

Interfacially initiated microemulsion copolymerization: One‐stage preparation of poly(n‐butyl methacrylate)–poly(N‐vinyl pyrrolidone) core–shell nanoparticles

Interfacially initiated microemulsion copolymerizations of n‐butyl methacrylate (BMA) and N‐vinyl pyrrolidone (NVP) by the redox initiation couple of benzoyl peroxide and ferrous sulfate were carried out with Tween 80 and n‐butanol as the surfactant and cosurfactant, respectively. Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy were recorded to analyze the chemical composition of the latex particles. Transmission electron microscopy was used to observe the particle morphology and dynamic light scattering to determine the particle size. The results demonstrated that interfacially initiated microemulsion polymerization prompted the copolymerization of the water‐soluble NVP monomer with the oil‐soluble BMA monomer to form core–shell nanoparticles. The influence of the surfactant concentration, BMA amount, and temperature on the particle size and polymerization rate was investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3751–3757, 2006     

Thermoresponsive poly(ϵ‐caprolactone)‐graft‐poly(N‐isopropylacrylamide) graft copolymers prepared by a combination of ring‐opening polymerization and sequential azide–alkyne click chemistry

A straightforward strategy is described to synthesize poly(?‐caprolactone)‐graft‐poly(N‐isopropylacrylamide) (PCL‐g‐PNIPAAm) amphiphilic graft copolymers consisting of potentially biodegradable polyester backbones and thermoresponsive grafting chains. PCL with pendent chlorides was prepared by ring‐opening polymerization, followed by conversion of the pendent chlorides to azides. Alkyne‐terminated PNIPAAm was synthesized by atom transfer radial polymerization. Then, the alkyne end‐functionalized PNIPAAm was grafted onto the PCL backbone by a copper‐catalyzed azide–alkyne cycloaddition. PCL‐g‐PNIPAAm graft copolymers self‐assembled into spherical micelles comprised of PCL cores and PNIPAAm coronas. The critical micelle concentrations of the graft copolymers were in the range 7.8–18.2 mg L^?1, depending on copolymer composition. Mean hydrodynamic diameters of micelles were in the range 65–135 nm, which increased as the length of grafting chains grew. PCL‐g‐PNIPAAm micelles were thermosensitive and aggregated upon heating. © 2014 Society of Chemical Industry     

Preparation of thermal‐responsive poly(propylene) membranes grafted with n‐isopropylacrylamide by plasma‐induced polymerization and their water permeation

Poly(propylene) (PP) membrane grafted with poly(N‐isopropylacrylamide) (PNIPAAm), which is known to have a lower critical solution temperature (LCST) at around 32°C, was prepared by the plasma‐induced graft polymerization technique. Graft polymerization of PNIPAAm onto a PP membrane was confirmed by microscopic attenuated total reflection/Fourier transform IR spectroscopy. The grafting yield of PNIPAAm increased with the concentration of N‐isopropylacrylamide monomer and the reaction time of graft polymerization. The average pore size of the PP membrane also affected the grafting yield. From the field emission scanning electron microscopy (FE‐SEM) measurement, we observed a morphological change in the PP‐g‐PNIPAAm membrane under wet conditions at 25°C below LCST. The permeability of water through the PP‐g‐PNIPAAm membrane was controlled by temperature. The PP‐g‐PNIPAAm membrane (PN05 and PN10) exhibited higher water permeability (L_p) than the original PP substrate membrane below LCST. As the temperature increased to above LCST, L_p gradually decreased. In addition, the graft yield of PNIPAAm and the average pore size of the PP substrate influenced water permeability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1168–1177, 2002; DOI 10.1002/app.10410     

Swelling and hydrolytic degradation behaviour of pH‐responsive hydrogels of poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] crosslinked by biodegradable polycaprolactone chains

BACKGROUND: Stimuli‐responsive hydrogels are typically obtained from non‐biodegradable monomers. The use of biodegradable crosslinkers can overcome this limitation. In this context, the main aim of this work was to use modified polycaprolactone as a crosslinker in the preparation of pH‐responsive hydrogels based on N‐isopropylacrylamide and methacrylic acid to give poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] (P(N‐iPAAm‐co‐MAA)). RESULTS: Poly(caprolactone) dimethacrylate macromonomer was synthesized and successfully employed as crosslinker with various ratios in the synthesis of well‐known pH‐responsive hydrogels of P(N‐iPAAm‐co‐MAA). The swelling properties of these degradable hydrogels were investigated. They practically do not swell at pH = 2, but exhibit a very high swelling capacity in distilled water and in solutions of pH = 7. In addition, degradation studies at pH = 12 showed that the hydrolysis of the ester groups in the polycaprolactone chains produces, after a relatively short time, the total solubilization of the polymer chains. CONCLUSION: The hydrogels under study have certain characteristics that could make them good candidates for use as matrices in controlled drug delivery. On the one hand, they do not swell in acid pH solution (stomach conditions) but they swell extensively at neutral pH. On the other hand, they became rapidly water soluble following degradation. Copyright © 2009 Society of Chemical Industry