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A new series of thermo-pH responsive polymers based on N-isopropylacrylamide and new cationic monomer has been synthesized from p-cresol in two facile steps and named by 2-((diethylamino)methyl)-4-methylphenyl acrylate), and abbreviated by (DEAMPA). It has been investigated by 1H NMR, 13C NMR, and FT IR. Three copolymers have been fabricated with three different molar concentrations of DEAMPA 5, 10, and 20 mol% using the free radical polymerization technique in solution. The copolymers have been chemically evaluated by 1H NMR and FT IR as well. Moreover, the physical characterizations were also investigated; the molecular weights and dispersity by GPC, the glass transition temperature by DSC, the change in the mass by decomposition using TGA, the degree of crystallinity by X-ray diffractions, and the morphological features by SEM. The change in the lower critical solution temperature and the phase separation of polymers solutions were measured by turbidity test as the change in transmittance with temperature with concerning the change in pH and using UV–VIS spectroscopy. The new cationic thermo-pH responsive copolymer will be used in the preparation of sensors, and dual responsive hydrogel.

Synthesis of new nanogels composed of poly N-isopropylacrylamide (PNIPAM) and poly N,N-diethylacrylamide (PNDEA) at different mole ratios of 100:0–50:50 were performed with constant acrylic acid (AA) content (NIPAM:AA mole ratio of 10:1) by free radical polymerization. The obtained nanogels were loaded with thymol and self-assembled on the surface of chitosan films to evaluate control release of the antimicrobial. The effect of temperature (8–35 °C), pH (2–8), and ions were evaluated on particle size (100–200 nm) and charge (−25--40 mv). With the increasing ratio of PNDEA in the copolymers, the lower critical solution temperature shifted gradually from 33 °C to 24 h) at 4 °C than that at 25 °C (around 6 h). All thymol loaded nanogels exhibited antimicrobial activity against E. coli and B. subtilis.

Here, we report the successful synthesis of series of stimuli responsive amphiphilic diblock copolymers (SRABCs) poly(N-isopropylacrylamide-b-N-vinylcarbazole) [poly(NIPAAm-b-NVK)] through reversible addition fragmentation chain transfer (RAFT) polymerization. Copolymers with fixed hydrophilic [poly(NIPAAm)] block length and variable (with three different) hydrophobic [poly(NVK)] block lengths were synthesized and the block length ratio was confirmed from their molecular weight data. The self-assembly nature of synthesized block copolymers was confirmed by determining critical micelle concentration (CMC). Self-assembled block copolymers showed rice-grain like morphology for copolymers having equivalent hydrophobic/hydrophilic chain length but in case of block copolymers having smaller and bigger hydrophobic chain length with respect to hydrophilic chain length displayed vesicular morphology. The thermo and pH responsiveness of the block copolymers was found to be influenced by variation in length and chemical composition of the blocks. Due to their thermo and pH responsiveness resulted self-assembled structures underwent morphology transitions from vesicular and rice grain like to micellar structure in aqueous medium. The probable applications of the studied stimuli responsive amphiphilic diblock copolymers can be found in the nanotechnology and biotechnology are indicated.

As a temperature-sensitive-discoloration hydrogel based on NIPAAm/HHPC was fabricated via two steps of electron beam radiation. Small nanomaterial such as GO and Fe2O3 were also added severally into the system of hydrogel as chromogenic agent. Different colors can be displayed in nanocomposite hydrogel system at the low, medium and high temperature respectively. The LCST of hydrogel system can be also adjusted precisely by the changes of irradiation dose of the prepolymer and composition ratio. Experimental results showed that the hydrogel can be changed quickly itself color in its near LCST. The microstructure and composition of nanocomposite hydrogel were characterized further by NMR, FTIR, TG, DSC, XRD, FE-SEM and XPS so as to reveal the mechanism of temperature-sensitive- discoloration. The novel NIPAAm/HHPC-based nanocomposite hydrogel is suitable especially to indicate different fever temperatures for fever patients and can be expected to as a new type of temperature-sensitive sensor and replace the traditional clinical thermometer.

Biodegradable cross-linker N-maleyl chitosan (N-MACH) was synthesized with chitosan (CS) and maleic anhydride (MA) by acylation. With N-MACH cross-linker, a series of cross-linked poly(N-isopropylacrylamide-co-itaconic acid) [P(NIPAAm-co-IA)] hydrogels were prepared, and their pH-and temperature-responsive behaviors, water contents, swelling/deswelling kinetics were investigated. By alternating the NIPAAm/IA weight ratios, hydrogels had the volume phase transition temperature (VPTT) changed from 33 to 38 °C, whereas cross-linking density did not affect the VPTT apparently. The water content of hydrogels was controlled by the monomer weight ratios of NIPAAm/IA, swelling media, and the cross-linking density. The results of the influence of pH value on the swelling behaviors showed that the minimum swelling ratios of the hydrogels appeared in neutral buffer solution, which was attributed to chemical composition of the hydrogels and the swelling media. In the swelling/deswelling kinetics, all the dried hydrogels exhibited fast swelling within 480 min and fast deswelling within 20 min, which was independent of the content of IA and cross-linker.

In the present study, a simple but effective strategy was introduced to synthesize pH and thermo double responsive poly(N-isopropylacrylamide-co-itaconic acid) P(NIPAAm-co-IA) hydrogels with improved properties through preparation in aqueous sodium chloride solutions. With the increase of concentration of NaCl, the phase separations of the gels became more and more pronounced, thus induced different chain conformations and network structures. The equilibrium swelling ratios and deswelling/reswelling kinetics of the hydrogels were investigated under conditions of different pH, temperature and ionic strength. The result showed these hydrogels were able to absorb large amounts of water and exhibit improved temperature and pH sensitivities, which may be ascribed to the formed porous network structures. Their chemical structures, lower critical solution temperatures (LCSTs) and surface morphologies were also checked by Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM).

Polymers containing functional biological activity groups have potential biological application. A new type of initiator (Glu-Br) synthesized by α-D-glucose and excessive 2-bromo-isobutyrlbromide was used to initiate NIPAM polymerization by atom transfer radical polymerization in DMF/Water mixture solvent, HMTETA as ligand and CuCl as catalyst. A star polymer was obtained with the reaction molar ratio of [NIPAM]0:[Glu-Br]0:[CuCl]0: [HMTETA]0 = 100:1:5:1. The polymerization reached a low polydispersity (PDI = 1.15–1.47) with the linearity plot of the Mn,GPC against conversion, and the reaction time revealed the well-controlled polymerization by ATRP. The LCST(lower critical solution temperature) of the star polymer was increased with the molecular weight increasing. Used fluorescein dye molecules as model drug to loaded in the star polymer to measure its envelope ability. The results indicated that the polymer has a promising application in the field of drug controlled release system.

Microstructured, temperature-sensitive poly(N-isopropylacrylamide) hydrogels were prepared with different proportions of poly(N-isopropylacrylamide) microparticles. The materials presented fast shrinkage at a temperature above their transition temperature (LCST = 32 °C), with highly reproducible swelling/shrinking cycles when temperature oscillates between below and above the LCST. They showed positive solute release control as a function of the temperature when small amount of microparticles were included in the hydrogels, making these hydrogels suitable for temperature controlled pulsatile drug release. The degree of crosslinking had a smaller impact than the percentage of microparticles in swelling and drug release in response to temperature. The inclusion of a small proportion of microparticles improved the mechanical propertied of the hydrogels. In addition, the polymerization steps are carried on in aqueous media, being a facile, scalable, and environmentally friendly technology.

Thermal-responsive hydrogels poly[(N-isopropylacrylamide)-co-(aminoethyl methacrylate β-cyclodextrin)] (PNiCD) were synthesized, and the morphology, thermal behavior and swelling/deswelling kinetic of the PNiCD hydrogels were studied. The results indicate that PNiCD hydrogels not only had considerable swelling ratios and rapid swelling/deswelling kinetics, but also behaved with fast thermal response sensitivities. In addition, by adjusting the weight ratio of GCD/NIPAAm ratio PNiCD hydrogels with different macroporous and thermal-responsive performances can be prepared for potential application in the biological medicine field. Levofloxacin lactate (LL) and rhodamine B (Rh) were elected as model drugs to explore controlled drug release for PNiCD hydrogels. The results showed that about 30 % of the LL and Rh were released within the first 30 min, and 80 % drugs were released at around 300 min, and this release process was faster than that of PNIPAAm hydrogel. The fast release performance indicated that these new CD modified PNIPAAm-based PNiCD hydrogels are promising for use in rapid drug delivery in the biological medicine field.

Radical copolymerization of N-isopropylacrylamide (NIPA) with N-vinyl-2-pyrrolidone (VP) were carried out with 2,2′-azobisisobutyronitrile (AIBN) as an intiator in N,N′-dimethylformamide solution at 65°C under nitrogen atmosphere. Compositon of the copolymers synthesized in a wide range of monomer feed ratios were determined by FTIR and 1H (13C) NMR-DEPT-135 spectroscopy. The monomer reactivity ratios were determined by Fineman-Ross, Kelen-Tudos and non-linear regression methods. It was observed that the studied monomer pair has some tendency to alternation in the chosen monomer feed ratios due to formation of intermolecular interaction through H-bonding and N → O = C coordination. The synthesized poly(NIPA-co-VP)s show temperature sensitivity (T s), higher glass-transiton temperature (T g ), thermal stability, polyelectrolyte and stimuli-responsive (temperature- and pH-sensitive) behavior and can be attributed to the class of bioengineering functional copolymers useful for application in various gene- and bioengineering processes, drug delivery systems and biomacromolecule conjugations.

Magnetic polymer particles have attracted much attention because of their ubiquitous use in biomedical field such as biomolecule separation, drug carriers, imaging and etc. Iron oxide magnetic nanoparticles were incorporated into temperature responsive poly (N-isopropylacrylamide) (PNIPAAm) polymer hydrogel by a seed polymerization following a surface modification step. Iron oxide magnetic nanoparticles (50–100 nm) prepared by co-precipitation method were modified with silica (SiO2) and 3-(trimethoxysilyl) propyl methacrylate (MPS) to introduce polymerizable vinyl group (−CH = CH2) at the surface of the nanoparticles. Then, the Fe3O4/SiO2/MPS particles were used as seed in polymerization of N-isopropylacrylamide (NIPAAm) and acrylic acid (AA). Here N, N’-methylenebisacrylamide (MBA) and potassium persulphate (KPS) were used as a cross-linker and initiator respectively. Dynamic Light scattering (DLS) results indicated a decrease of hydrodynamic diameter of magnetic Fe3O4/SiO2/MPS/poly (NIPAAm-AA) polymer particles with increasing temperature. Surface functionality and polymer coating, morphology, chemical composition and presence of iron oxide in the magnetic polymer particles were evaluated by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) respectively. The content of magnetic part was more than 50 wt.% determined by TGA, satisfactory for separation of the final particles from a dispersed media by external magnet. Therefore, the magnetic polymer particles prepared here could be a potential candidate for separation technology.

In this paper, the temperature-sensitive luminescent particles with core-shell structure were synthesized by grafting poly (N-isopropylacrylamide) (PNIPAM) to the exterior surface of lanthanide-polyoxometalates (Ln-POM). The Ln-POM/PNIPAM nanoparticles were characterized by FT-IR, UV–vis spectra, thermogravimetric analysis, transmission electron microscopy, scanning electron microscope, dynamic light scattering and luminescence spectra. The results showed that the smart nanoparticles were spherical and had fine core-shell structure. The luminescent spectra showed that the luminescence properties of smart Ln-POM/PNIPAM nanoparticles were changeable in response to temperature stimuli. The luminescent nanoparticles have potential applications in luminescent probes and labels for biomedicine.

Thermosensitive, amphiphilic, star-shaped poly (e-caprolactone)-block-poly (N-isopropylacrylamide) with prophyrin-core (SPPCL-b-PNIPAAm) was synthesized by ring-opening polymerization (ROP) and reversible addition-fragmentation chain transfer polymerization (RAFT) and characterized by NMR, IR, GPC in this study. The optical transmittance results showed that the lower critical solution temperatures (LCST) of the copolymer solutions were attractively close to normal physiologic temperature at around 37 °C. Due to its amphiphilic property, the obtained SPPCL-b-PNIPAAm had a low critical micelle concentration (CMC) in an aqueous solution and self-assembled into micelles in water. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis of micelle morphology revealed a well-defined spherical shape with a diameter of around 100 nm. Moreover, SPPCL-b-PNIPAAm micelles obtained high singlet oxygen quantum yields and indicated a sensitivity to temperature, suggesting that the SPPCL-b-PNIPAAm was a stimulus-responsive photosensitizer which had a potential application in targeted photodynamic therapy.

In this study we used Fourier transform infrared (FTIR) spectroscopy to investigate the phase behavior of poly(N-isopropylacrylamide) (PNIPAM) in mixed solvents comprising D2O and tetrahydrofuran-d 8(THF-d8). The signals of the CH3 groups of the N-isopropyl amide unit and the CH2 groups on the main chain and those in the amide I region of the PNIPAM provided details about the various hydrophobic and hydrophilic interactions in the mixed aqueous solution. Upon increasing the volume fraction of THF-d 8 (x v) from 0 to 11 %, coil-to-globule transition occurred as a result of dehydration and hydrophobic interactions among the hydrophobic groups of the PNIPAM chain, followed by induced aggregation and collapse of the PNIPAM chain. When the value of x v was in the range of 11 to 55 % the hydrophobic groups formed hydrophobic cages that prevented diffusion of D2O molecules and the formation of hydrogen bonds with the amide I units of the PNIPAM chains. Meanwhile, the hydration sphere of THF-d 8 also hindered the hydrophobic–hydrophobic interactions between THD-d 8 and the PNIPAM; consequently, the PNIPAM chains shrank as they aggregated. The PNIPAM solution was homogenized again at values of x v greater than 55 %, due to hydrophobic–hydrophobic interactions among the free THD-d 8 molecules and the hydrophobic groups of the PNIPAM. We believe that dehydration of the hydrophobic groups rather than inter- and intrachain hydrogen bonding was the major driving force behind the aggregation and coil-to-globule transitions.

Interpenetrating polymer networks (IPN) consisting of pH-sensitive carboxymethyl pullulan (CMP) and thermosensitive poly(N-isopropylacrylamide) (PNIPAAm) were synthesized through a two-step procedure by chemical cross-linking of NIPAAm in the presence of CMP, followed by additional reticulation of the polysaccharide. The hydrogels were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and swelling measurements. Swelling properties of the hydrogels were studied at equilibrium, by investigating pH- and temperature-dependence, dynamic swelling ratio and pulsatile swelling-deswelling kinetics. It was found that IPN hydrogels responded to both temperature and pH changes and such stimuli-responsiveness was reversible. At pH 1.2 and temperature values lower than VPTT, the swelling ratios of IPN hydrogels are smaller than that of pure PNIPAAm because most of the carboxylic groups are protonated forming hydrogen bonds with other carboxylic or amide groups of PNIPAAm. Conversely, in phosphate buffer solutions at pH 7.4, the swelling ratios of IPN hydrogels are higher than that of pure PNIPAAm. In this case, the carboxylic groups of CMP are ionized; therefore, the hydrogen bonds are broken and the electrostatic repulsions lead to a more expanded network. The loading and release profiles of a model drug namely, diphenhydramine (DPH), were also evaluated. The results showed that the release rate of DPH was higher at pH 10 buffer solution than at pH 7.4 and 1.2, at 37 °C. In pseudo physiological conditions, DPH was quickly released from the hydrogel at 20 °C, and showed a sustained release profile at 37 °C.

The incorporation of modified β-cyclodextrin (β-CD) into a poly(N-isopropylacrylamide) (PNIPAAm)/chitosan (PNCS) nanohydrogel was studied. β-CD was functionalized with acrylic groups, with different numbers of vinyl bonds added per β-CD molecule. The surfactant-free dispersion polymerization (SFDP) semi-batch method was used to synthesize the nanohydrogel. Increasing the number of vinyl groups per β-CDAC (β-CD acrylate) molecule induced the formation of smaller nanogels with diameters ranging from 142 to 68 nm. The cyclodextrin-modified dual-responsive nanogels obtained presented an LCST (lower critical solution temperature) in aqueous medium at around 31 °C. The incorporation of β-CDAC into the nanohydrogel networks was demonstrated using the phenolphthalein titration method. The diameters of the nanohydrogels changed upon varying the pH and temperature of the swelling medium. In order to investigate the release behavior of the nanohydrogels, methylene blue and phenolphthalein were employed as hydrophilic and hydrophobic model drugs. The results showed that the drug loading achieved with the hydrophobic drug was higher than that achived with the hydrophilic drug. The properties of the final nanohydrogels were investigated with FTIR, FESEM, CHNO analysis, DSC, and DLS.

Temperature-sensitive poly(N-isopropylacrylamide)/polyethylene oxide (PNIPAAm/PEO) nanocomposite hydrogels were successfully synthesized using γ-radiation as the initiator and crosslinking agent. The temperature-dependent swelling and shrinking behavior of PNIPAAm/PEO was exploited in order to form silver nanoparticles within the hydrogel network. Loading-temperature-responsive hybrid microgels containing silver nanoparticles (AgNPs) were readily prepared by the in situ reduction of Ag+ ions within and coordinated to PNIPAAm/PEO hydrogels. A novel method—irradiation—was utilized to generate AgNPs within the previously obtained hydrogel matrix. The newly prepared Ag-NPs/PNIPAAm/PEO hydrogels exhibited much better temperature-sensitive properties than conventional polymers. The PNIPAAm hydrogels thus prepared exhibited properties such as pore size, equilibrium swelling ratio, and swelling/deswelling rates that could be varied by modifying the feed weight ratio of NIPAAm to PEO. UV-Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) measurements confirmed that the hydrogel possessed nanostructure, and FTIR was employed to characterize the components of the resulting nanoobjects. The hydrodynamic diameter and morphology of the microgel particles were examined by dynamic light scattering (DLS) and scanning electron microscopy (SEM), respectively. At room temperature, the hydrodynamic diameter of the PNIPAAm/PEO polymer was measured as 3.0 ± 0.7 μm, while that of the PNIPAAm/PEO-stabilized AgNPs was found to be 1.8 ± 0.1 μm. Twenty-five percent of the silver nanoparticles were less than 64.9 nm in diameter, and the mean of the particle size was 9.6 nm. These stimuli-responsive nanocomposite hydrogels have potential applications in biomedicine; for example, they could be used as drug-delivery matrices.

An amphiphilic graft copolymer (PVDF-g-PNIPAAm) with poly(vinylidene fluoride) (PVDF) main chains and poly(N-isopropylacrylamide) (PNIPAAm) side chains was synthesized via radical copolymerization, and flat sheet membranes of this copolymer were prepared by the phase inversion method. The process of membrane formation was investigated by ultrasonic time-domain reflectometry (UTDR). The structures and properties of the membrane, including its surface chemical structure, pore morphology, and water permeability, were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and a water permeation experiment, respectively. The relationship between the process of membrane formation and the properties of the membrane was studied. The results showed that the membrane displayed temperature sensitivity. Treating the PVDF for a longer period with alkali caused more PNIPAAm to graft onto the main chains, which influenced not only the microporous structure and formation process of the membrane but also the temperature sensitivity of the performance of the membrane.

pH- and thermal-sensitive hydrogels were synthesized by copolymerization of acrylic acid and N-isopropylacrylamide with a modified β-CD crosslinker in aqueous solutions. The swelling behaviors of the hydrogels at different temperatures and pHs were examined. The hydrogels shrink in acidic conditions or at temperatures above their collapse temperature and swell in neutral or basic media or at lower temperatures. These processes can be reversed by changing the pH or temperature. Using bovine serum albumin as the model protein drug, in vitro drug release experiments were carried out at different pH values and temperatures. The pH- and temperature-dependent release behaviors indicate that these materials show much promise as stimuli-responsive drug delivery carriers.

A series of novel temperature- and pH- responsive water-soluble graft copolymers, casein-g-poly(N-isopropylacrylamide)(PNIPAAm), were prepared via a direct graft copolymerization of N-Isopropylacrylamide (NIPAAm) from casein. The polymerization was induced by tert-butyl hydroperoxide (TBHP) in water at general condition. Chemical structures of the graft copolymers were characterized by Fourier transform infrared spectra (FTIR), Thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect elements on graft copolymerization, such as concentration of initiator, reaction time, reaction temperature and ratio of NIPAAm to casein were investigated in terms of NIPAAm conversion, grafting percentage (GP) and grafting efficiency (GE), respectively. The graft copolymers are stimuli-sensitive with respect to both temperature and pH in aqueous solutions. It could self-assembly into core-shell particles in aqueous solution with collapsed PNIPAAm as core as well as inverse core-hair particles with expanded casein as core on changing temperature or pH, as indicated by transmission electron microscopy (TEM).