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A series of block copolymers of acrylamide and N-isopropylacrylamide (NIPAM) characterized by different ratios between the length of the two blocks have been prepared through atomic transfer radical polymerization in water at room temperature. The solution properties of the block copolymers were correlated to their chemical structure. The effect of the hydrophilic/hydrophobic balance on the critical micelle concentration (CMC) was investigated. The CMC increases at higher values for the solubility parameter, thus indicating a clear relationship between these two variables. In addition, the solution rheology (in water) of the block copolymers was studied to identify the effect of the chemical structure on the thermo-responsiveness of the solutions. An increase in the length of the PNIPAM block leads to a more pronounced increase in the solution viscosity. This is discussed in the general frame of hydrophobic interactions strength. The prepared polymers are in principle suitable for applications in many fields, particularly in enhanced oil recovery. (C) 2013 Wiley Periodicals, Inc.

Poly(N-isopropylacrylamide) (PNIPAM) microgels were prepared through soap-free emulsion polymerization using 2, 2′- azobisobutyronitrile and potassium persulfate as initiator respectively. The thermal response of microgels was researched by measuring the transmittance and the hydrodynamic diameter of the microgels at different temperatures. The result shows that the different structure of the end groups of polymer that come from residues of initiator result in the different thermal response of PNIPAM microgels. The LCST (lower critical solution temperature) of AIBN-initiator microgels is 5°C lower than that of the KPS-initiator microgels, whereas the AIBN-initiated PNIPAM microgels have better thermal response sensitivity. The scanning electron microscope characterization shows that the morphology of AIBN-initiated PNIPAM microgels is more regular than that of KPS-initiated. Furthermore, the Tg of the microgels was measured by differential scanning calorimeter and the result indicates that the end groups influences the Tg of microgels severely. This work demonstrated that the hydrophobic end group coming from initiators can decreases the LCST of PNIPAM microgels and increases the thermal response sensitivity, which providing a newly simple but effective method to regulate the thermal response of PNIPAM microgels. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1164-1171, 2013

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 H-1-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. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Macroporous monoliths, composed of thermoresponsive, tertiary-aminated, and crosslinking monomers, were prepared for continuous-flow separation of palladium(II) ions. N-Isopropylacrylamide was required to form the porous structure in the monoliths, indicating that the mechanism of porous structure formation involved polymerization-induced phase separation of the poly(N-isopropylacrylamide) gel. Tertiary-aminated monoliths showed adsorption selectivity for palladium(II) ions in hydrochloric media, compared with copper(II) ions. The maximum capacities of the monoliths with tertiary amine contents of 10, 20, 30, and 70 mol % for palladium(II) ions were 0.6, 1.1, 1.3, and 2.3 mmol/g, respectively. Darcy's permeabilities of water through the macroporous monolith were 10−14 to 10−13 m2, and those were comparable to that through a commercially available membrane filter with a pore size of several micrometers. In the continuous-flow process, the macroporous monolith with tertiary amine selectively adsorbed palladium(II) ions in the coexistence of copper(II) ions with 10 times higher concentration than the palladium(II) ions. The palladium(II) ions were eluted from the macroporous monolith, and the concentration of palladium(II) ions in the eluate was up to 45 times of that in the feed solution. The average enrichment factor and total recovery percentage of palladium(II) ions were 8.7 times and 95%, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44385.

Temperature- and NIR irradiation-responsive microparticles composed of cinnamoyl poly(N-isopropylacrylamide-co-hydroxyethylacrylate) [CinP(NIPAM-HEA)] and gold nanoparticle (GNP) were prepared by a spray-drying method. According to the cloud points determined by an optical method, the HEA content in P(NIPAM-HEA) had no marked effect on the lower critical solution temperature (LCST). However, the cinnamoyl group content in CinP(NIPAM-HEA) had a significant effect on the LCST. The LCSTs determined by a calorimetric method was in agreement with those determined by an optical method. The hydrodynamic mean diameter of gold nanoparticle (GNP) prepared by reducing gold ions was about 30 nm and it seemed to be a nanosphere on TEM photo. Spray-dried CinP(NIPAM-HEA) microparticles containing GNP was 1.5 μm to 12 μm in diameter on SEM photo. Gold was detected on the energy-dispersive X-ray spectrum of the microparticles. The amount of FITC-dextran released for 12 h from the microparticles was much higher at temperatures above the LCST (at 37 °C and 45 °C) than below the LCST (at 20 °C and 25 °C). The cumulative release amount in 12 h was only about 3% without NIR irradiation, whereas the value was about 26.5% when NIR was irradiated to the microparticle suspension. The photothermal energy generated by GNP was believed to render the thermosensitive copolymers de-swollen and hydrophobic, allowing for the active release of dye from the microparticles. The NIR irradiation-responsive GNP-loaded microparticles could be applied to the development of NIR-responsive drug carriers which release their contents in response to an external stimulus (i.e., NIR irradiation). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44141.

Poly(N-isopropylacrylamide) (PNIPAAm)/calcium carbonate (CaCO3) micro/nanohybrid composites with smart drug-delivery property had been prepared via in situ biomineralization reaction. Sodium poly(styrene sulfonate) (PSS) was used as the crystal growth additive to control the crystalline polymorph of CaCO3 and the morphology of the hybrid materials. The interaction between PSS and Ca2+ contributed to the formation of hierarchical micro/nanohybrid composites, in which microscale vaterite microparticles were covered by nanoscale PNIPAAm micelle. Vitamin B2 (VB2) release behavior was found to be pH- and thermal-responsive. Moreover, the release profiles were sustained with the introduction of CaCO3 microparticles, suggesting that CaCO3 microparticles could hinder the permeation of the encapsulated VB2 and reduce the drug release effectively. The prepared micro/nanohybrid materials can be used as “smart” hierarchical materials for controlled drug delivery. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (PEG-b-PNIPAM) block copolymers were synthesized by atom transfer radical polymerization, and the α-cyclodextrin (α-CD) induced self-assembly characteristics of the system were elucidated. Below the lower critical solution temperature (LCST) of PNIPAM, CD threaded onto the PEG segments and induced micellization to form rod-shaped nanostructures comprising of a PEG/α-CD condensed phase and a PNIPAM shell. Increasing the temperature of system above the LCST caused the PNIPAM segments to collapse, which resulted in the dethreading of the CD. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A novel copolymer, poly(N-isopropylacrylamide-co-hydroxypropyl methacrylate-co-3-trimethoxysilypropyl methacrylate) has been synthesized and the hydrodynamic diameters in various aqueous solutions under different temperatures are determined by dynamic light scattering. The results show that the hydrodynamic diameters of copolymers have no obvious change in each working solution below lower critical solution temperature (LCST); across LCST, the diameters increased suddenly at different initial temperature in various aqueous solutions; above LCST, they decreased slightly as the temperature increased in UHQ water, and increased continuously with increasing temperature or salt concentration in saline solutions, and reduced with the rising of pH value in pH buffer. These are attributed to different intermolecular and intramolecular forces leading to disparity in dimension, conformation, and LCST of copolymers. The hydrogen bonding between water molecules and copolymer chains could maintain size and conformation of copolymer single chain; the hydrogen bonding between amide linkages and hydrophobic interactions between isopropyl groups result in intramolecular collapse and intermolecular aggregation; the electrostatic repulsion weakens aggregation extent of copolymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Stimuli-responsive biocompatible and biodegradable materials can be obtained by combining polysaccharides with polymers exhibiting lower critical solution temperature (LCST) phase behavior, such as poly(N-isopropylacrylamide) (PNIPAAm). The behavior of aqueous solutions of sodium alginate (NaAl) grafted with PNIPAAm (NaAl-g-PNIPAAm) copolymers as a function of composition and temperature is presented. The products obtained exhibit a remarkable thermothickening behavior in aqueous solutions if the degree of grafting, the concentration, and the temperature are higher than some critical values. The sol-gel-phase transition temperatures have been determined. It was found that at temperatures below LCST the systems behave like a solution, whereas at temperatures above LCST, the solutions behave like a stiff gel, because of PNIPAAm segregation. This behavior is reversible and could find applications in tissue en- gineering and drug delivery systems. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 3340-3348, 2013

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol–water mixture. A scanning electron microscopy study revealed that the freeze-dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X0.43>X0.21>X0.76 ≈ X0.57>X0.31>X0.13>X0.06>X0, where Xm denotes a gel prepared in a methanol–water mixture with m mole fraction of methanol (xm). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all the PNIPAM gels in the methanol–water mixtures with different xm values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.43> X0.31> X0.21> X0.57> X0.76 ≈ X0.13> X0.06> X0. The reswelling rates of these hydrogels decreased in the following order: X0> X0.31> X0.06 ≈ X0.13 > X0.76> X0.57> X0.21> X0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug-loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Microgels were prepared by taking advantage of electrostatic interaction between poly(N-isopropylacrylamide-co-methacrylic acid) and poly(N-isopropylacrylamide-co-dimethylaminoethylmethacrylate). The maximum interaction, investigated by measuring the size of complex and the turbidity of the mixture, took place at pH = 6.5. The microgel prepared at pH = 6.5 using the copolymer ratio of 1/1 (w/w) was globular on scanning electron microscopy, and the size was a few to tens of micrometer. The phase transition of the microgel, observed by turbidometry and differential scanning calorimetry, occurred around 31°C. % Release, in 24 h at room temperature, of FITC-dextran from the microgel was higher under an acidic (64% at pH = 4.0) and an alkali condition (69 % at pH = 9.0) than the % release at pH = 6.5 (41%). The disintegration of microgels would be responsible for the higher % release. The % releases, in 24 h at pH = 6.5, were lower at higher temperatures (53% at 35°C, 50% at 40°C) than at lower temperatures (71% at 25°C, 61% at 30°C). The suppressed release at higher temperatures is possibly due to the skin formation on the surface of microgel. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

This work refers to the synthesis and characterization of thermosensitive hydrogels based on interpenetrating polymer networks (IPNs) of poly(N-isopropylacrylamide) (PNIPAAm) and calcium alginate in the form of films. The influence of the crosslinking degree of PNIPAAm and alginate content on thermal, swelling, mechanical, and morphological properties of hydrogels is investigated in detail. Characterization of pure PNIPAAm hydrogels and IPN hydrogels was performed by FTIR, DSC, DMA, and SEM. In addition, the studies of equilibrium swelling behavior as well as swelling, deswelling, and reswelling kinetics are performed. The results obtained imply the benefits of synthesizing IPNs based on PNIPAAm and calcium alginate over pure PNIPAAm hydrogels. The presence of calcium alginate contributes to the improvement of mechanical properties, the deswelling rate of hydrogels, and the network porosity, without altering the thermosensitivity of PNIPAAm significantly. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A new strategy was developed to prepare thermo- and pH-sensitive hydrogels by the crosslinking of poly(N-isopropylacrylamide) with a biodegradable crosslinker derived from poly(L-glutamic acid). Hydrogels were fabricated by exposing aqueous solutions of precursor containing photoinitiator to UV light irradiation. The swelling behaviors of hydrogels at different temperatures, pHs, and ionic strengths were examined. The hydrogels shrank under acidic condition or at temperature above their collapse temperature and would swell in neutral or basic media or at lower temperature. These processes were reversible as the pH or temperature changed. All hydrogels exhibited no weight loss in the simulated gastric fluid but degraded rapidly in the simulated intestinal condition. Bovine serum albumin were used as a model protein drug and loaded into the hydrogels. The in vitro drug release experiment was carried out at different pH values and temperatures. The pH and temperature dependent release behaviors indicated the promising application of these materials as stimuli-responsive drug delivery vehicles. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Polyaniline-graft-Poly(N-isopropylacrylamide) copolymers were synthesized by atom-transfer radical polymerization (ATRP) of N-isopropylacrylamide using polyaniline macro-initiators. Polyaniline-chloroacetylchloride and polyaniline-chloropropionylchloride macroinitiators were obtained by the reaction of amine nitrogens of polyaniline with chloroacetyl chloride and 2-choloropropionyl choloride, respectively. Both macroinitiators and graft copolymers were characterized by FT-IR and 1H-NMR spectroscopy. The cyclic voltammetry (CV) and UV-Vis spectroscopy studies showed that these copolymers are electroactive. The solubility test revealed that the polyaniline-graft-poly (N-isopropylacrylamide) copolymers are water soluble or water/methanol soluble. The Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) images showed the growing of poly (N-isopropylacrylamide) chains on polyaniline backbone. Investigation of thermal behavior of graft copolymers by thermal gravimetry analysis (TGA) confirmed the results obtained from AFM and SEM images. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Poly(N-isopropylacrylamide-co-hydroxyethyl methacrylate) [P(NIPAM-co-HEMA)] copolymer was synthesized by controlled radical polymerization from respective N-isopropylacrylamide (NIPAM) and hydroxyethyl methacrylate (HEMA) monomers with a predetermined ratio. To prepare the thermosensitive and biodegradable nanoparticles, new thermosensitive graft copolymer, poly(L-lactide)-graft-poly(N-isoporylacrylamide-co-hydroxyethyl methacrylate) [PLLA-g-P(NIPAM-co-HEMA)], with the lower critical solution temperature (LCST) near the normal body temperature, was synthesized by ring opening polymerization of L-lactide in the presence of P(NIPAM-co-HEMA). The amphiphilic property of the graft copolymers was formed by the grafting of the PLLA hydrophobic chains onto the PNIPAM based hydrophilic backbone. Therefore, the graft copolymers can self-assemble into uniformly spherical micelles o about 150–240 nm in diameter as observed by the field emission scanning electron microscope and dynamic light scattering. Dexamethasone can be loaded into these nanostructures during dialysis with a relative high loading capacity and its in vitro release depends on temperature. Above the LCST, most of the drugs were released from the drug-loaded micelles, whereas a large amount of drugs still remains in the micelles after 48 h below the LCST. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Controlled thermoresponsive PET track-etched membranes were synthesized by grafting N-isopropylacrylamide (NIPAAm) onto the membrane surface via atom transfer radical polymerization (ATRP). The initial measurements were made to determine the anchoring of ATRP initiator on PET membrane surface. Thereafter, polymerization was carried out to control the mass of polymer by controlling reaction time grafted from the membrane surface and, ATR-FTIR, grafting degree measurements, water contact angle measurements, TGA, and SEM were used to characterize changes in the chemical functionality, surface and pore morphology of membranes as a result of modification. Water flux measurements were used to evaluate the thermoresponsive capacity of grafted membranes. The results show the grafted PET track-etched membranes exhibit rapid and reversible response of permeability to environmental temperature, and its permeability could be controlled by controlling polymerization time using ATRP method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Supermacroporous poly(N-isopropylacrylamide) (PNIPAAm) cryogels containing urease were prepared via UV irradiation technique and hydrogen peroxide as initiator. Specifically, due to the cryostructuration phenomenon urease molecules were embedded into the dense cryogel walls. Thus, although the enzyme is physically entrapped, the system exhibited remarkable resistance against leaking due to the dense polymer network formed in the cryogel walls. The immobilized urease can catalyze the hydrolysis of urea in a broad temperature range in both batch and flow regime. The interconnected macropores assist for unhindered diffusion of the substrate and reaction products through the gel, thus, paving the way for consecutive reuse at a constant activity, in contrast to the conventional PNIPAAm hydrogel. Due to the spongy-like morphology PNIPAAm cryogels containing urease can be exploited as highly permeable membrane for direct removal of traces of urea from continuously flowing feed solutions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

In this study, a semi-interpenetrating polymer network (semi-IPN) gel comprising a crosslinked amphiphilic N,N-dimethylacrylamide-co-N-isopropylacrylamide gel and interpenetrating thermosensitive poly(N-isopropylacrylamide) (poly(NIPAM)) was prepared. Their thermosensitive behaviors in a buffer solution comprising sodium chloride, sodium citrate, and sodium dodecyl sulfate, which are generally used in biochips, were investigated. At low temperatures, the gel in the buffer solution was absolutely transparent. However, when the gel was heated, it became milky white or opaque without changes in the gel size. It is well known that the network or crosslink distribution of the transparent gel is homogeneous macroscopically, whereas that of the opaque gel is inhomogeneous; in other words, the network of the opaque gel consists of coarse and dense parts. The structural changes in the gel network were confirmed by the temperature dependence of the permeability of the buffer solution through the semi-IPN gel membrane. The permeability increased stepwise when the gel became opaque due to heating. The structural changes in the semi-IPN gel network depended on the compositions of the buffer solution and gel, i.e., the copolymerization ratio of NIPAM in the gel and the content of the poly(NIPAM) molecules in the gel. These results suggest that the thermosensitive behaviors of the semi-IPN gel strongly depend on the interactions between the copolymerized NIPAM in the gel network and the poly(NIPAM) molecules. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

To improve the mechanical strength of natural hydrogels and to obtain a sustained drug-delivery device, temperature-/pH-sensitive hydrogel beads composed of calcium alginate (Ca-alginate) and poly(N-isopropylacrylamide) (PNIPAAm) were prepared in the presence of poly(sodium acrylate) (PAANa) with ultrahigh molecular weight (Mη ≥ 1.0 × 107) as a strengthening agent. The influence of PAANa content on the properties, including the beads stability, swelling, and drug-release behaviors, of the hydrogels was evaluated. Scanning electron microscopy and oscillation experiments were used to analyze the structure and mechanical stability of the hydrogel beads, respectively. The results show that stability of the obtained Ca-alginate/PNIPAAm hydrogel beads strengthened by PAANa the alginate/poly(N-isopropyl acrylamide) hydrogel bead (SANBs) was significantly improved compared to that of the beads without PAANa (NANBs) at pH 7.4. The swelling behavior and drug-release capability of the SANBs were markedly dependent on the PAANa content and on the environmental temperature and pH. The bead sample with a higher percentage of PAANa exhibited a lower swelling rate and slower drug release. The drug release profiles from SANBs were further studied in simulated intestinal fluid, and the results demonstrated here suggest that SANBs could serve as a potential candidate for controlled drug delivery in vivo. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Poly(N-isopropylacrylamide-co-acrylic acid) (poly(NIPAM-co-AA)) microgels with different copolymer compositions were prepared through soap-free emulsion polymerization at 80°C, and 2, 2'-azobisisobutyronitrile (AIBN) was used as initiator. Scanning electron microscope (SEM) characterization shows that the prepared microgels are regular and smooth and not easy to distort. Result of 1 H-NMR characterization shows that with increasing of the initial concentration of AA (AA in feed), the AA content in polymer chains increases. The thermal response of microgels latex was investigated by UV-3010 spectrophometer through detecting the transmittance of the latex at different temperature in the range of 190-900 nm. The thermal response of the poly(NIPAM-co-AA) microgels was tested by dynamic light scattering (DLS). The results show that with the increase of AA content in polymer chains, the low critical solution temperature (LCST) of microgels latex first decreases and then increases. Still, with increasing of AA in poly(NIPAM-co-AA) microgels, the LCST of microgels first increases and then decreases. The basic reasons causing the changes of LCST of microgels latex and microgels are interpreted clearly in this article from the perspective of hydrogen bonding interaction.

The use of surfaces with tunable properties triggered by external stimuli is effective in controlling the interactions between biomaterials and biological entities, such as proteins and cells. The goal of this work is to prove that the presence of poly-n-isopropylacrylamide (P-N-IPAAm) chains grafted onto polyurethane (PU) membranes and used for medical wound dressings can allow the behavior of the surfaces to be shifted from hydrophobic to hydrophilic by reducing the temperature to values lower than the low critical solution temperature (LCST) of the polymer, which is close to 32°C. The manipulation of this behavior can then be used to control cell and protein adhesion on the surface. Grafting of P-N-IPAAm was accomplished by treating the surface of polyurethane membranes with ultraviolet (UV) radiation, followed by polymerizing the isopropylacrylamide from the modified surfaces. The wettability of the surfaces was studied using contact angle measurements as a function of temperature. Infrared spectroscopy was also used to characterize these modified surfaces. The ability of the grafted surfaces to allow adsorption of proteins was evaluated as a function of temperature. The results showed that the amount of proteins adsorbed on the polyurethane membranes could be radically changed by altering the temperature above or below 32°C. In vivo biocompatibility tests were performed on P-N-IPPAm samples, and no indication of toxicity was noted after 7 days of implantation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Modified chondroitin sulfate (p-CdS) microspheres were synthesized by way of crosslinking- copolymerization reaction with N-isopropylacrylamide (NIPAAm), yielding CdS-co-PNIPAAm copolymer net- work. The incorporation of vinyl groups onto the CdS was processed with the use of glycidyl methacrylate (GMA) in an aqueous solution of pH 3.5 under stirring speed of 800 rpm at 50 � C. 13 C NMR and 1 H NMR spectra of CdS treated with the GMA indicated the formation of 3-metha- cryloyl-1-glyceryl ester of p-CdS and 3-methacryloyl-2- glyceryl ester of p-CdS that are the reaction products resultant of an epoxide ring-opening mechanism via. The synthesis of microspheres was performed via radical reac- tion of the vinyl groups at the p-CdS with vinyl groups at the NIPAAm in a waterbenzyl alcohol microemulsion. The formation of spherical structures is the result of the polymerization-crosslinking reaction of the p-CdS with the NIPAAm monomers at the droplets of water, in view that both reactants have hydrophilic characteristics at the tem- perature at which the reaction was processed. The pure CdS hydrogel microspheres showed a slightly cracked structure with a lower diameter range while the CdS-co- PNIPAAm hydrogel microspheres showed a flat and tight structure with a more regular mass distribution. V C 2011

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were prepared by free-radical polymerization in different ethanol–water mixtures. A scanning electron microscopy study revealed that the resulting hydrogels were macroporous. The swelling ratios of the resultant hydrogels in water at 20°C followed this order: X0.34 ≈ X0.68 > X0.48 > X0.09 > X0.04 > X0, where Xa denotes a gel prepared in an ethanol–water solvent mixture with an ethanol molar fraction of a. Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with increasing temperature. The complete collapse of the PNIPAM chain of all of these gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all of the PNIPAM gels with different molar fractions of ethanol at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.34 > X0.48 > X0.68 > X 0.09 > X0.04 > X0. The reswelling rates of these hydrogels decreased in the following order: X0 > X0.04 ≈ X0.48 > X0.09 ≈ X0.68 > X 0.34. The freeze-drying process decreased the swelling ratios but increased the deswelling and reswelling properties of the PNIPAM gels. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

This article described the preparation of temperature-responsive chromatographic column containing poly(N-isopropylacrylamide) and poly quaternary ammonium salt. Poly (N-isopropylacrylamide) and poly ([2-(methacryloyloxy)ethyl]trimetylammonium chloride) were synthesized and grafted to amino modified silica gel. The temperature responsive polymer grafted silica gel was characterized using Fourier transform infrared spectroscopy, thermoweight loss, and elemental analysis. The temperature responsive chromatographic column was used to analyze lactic acid and creatine phosphate disodium salt by controlling of the column temperature from 10 to 50°C. The mixture of lactic acid and creatine phosphate disodium salt was baseline separated at pH 6.93. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

A series of the thermosensitive interpenetrating polymer network hydrogels composed of soy protein and poly(N-isopropylacrylamide) were successfully prepared. The structure and properties were systematically characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and differential scanning calorimetry. It was found that the hydrogels had good miscibility and high porosity, and the volume phase transition temperatures of the hydrogels were around 32°C. The release behavior and the release mechanism of a model protein, bovine serum albumin (BSA), were also investigated in detail. The results indicated that the release behavior of BSA had strong temperature dependence and the release percentage of BSA could be controlled by modulating the amount of soy protein or crosslinking agent. The analysis of the release mechanism revealed that the Fickian diffusion controlled release was dominant under the experimental conditions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Poly[N-isopropylacrylamide-co-[2-(methylthio)ethyl methacrylate]], poly(NIPA-co-MTEMA) gels were prepared by free radical polymerization in aqueous solution. The homogeneous and heterogeneous gels were prepared by using 10 mM MTEMA in 5.0%(v/v) ethanol at 10°C and 30 mM MTEMA in 20%(v/v) ethanol at 50°C, in 1.0 and 1.5M NIPA solution, respectively. Homogeneous and heterogeneous gels had swelling ratios at 540 ± 28% and 551 ± 37%, respectively. The extraction of Au(III) ion was studied in batch method. The optimum pHs for the extraction of Au(III) by homogeneous and heterogeneous gels were 1–3 and 1–5, respectively. The suitable extraction time was 3 h at 50°C when using a rod-shaped copolymer (0.7 cm diameter and 1 cm length). The adsorption behavior obeyed the Langmuir and Freundlich isotherms. The maximum sorption capacities of Au(III) onto homogeneous and heterogeneous gels were 62.8 and 322 μmol/g, respectively. The desorption equilibrium was reached within 2–3 h at 10°C by 0.1M thiourea in 5%(v/v) HCl. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Copolymers of N-isopropylacrylamide and octadecyl acrylate (PNO), of which the content of octadecyl acrylate (ODA) was 1.3% (PNO 1.5), 1.7% (PNO 2.0), and 3.0% (PNO 4.0), were prepared using a free radical reaction. Various assemblies were obtained depending on the concentration of PNOs and the contents of ODA. Hydrophobic interaction between ODA residues is likely to act as crosslinker. PNO 1.5 formed hydrogel at the concentration of 7%. With PNO 2.0, hydrogels were formed when the concentration was 5 and 7%. With PNO 4.0, the opaque gel was obtained when the concentration was 7%. Upon heating across the lower critical solution temperature, the hydrogels shrank but the opaque gel was broken down into a suspension. At 40°C, the release degrees of fluorescein isothiocyanate-dextran were much smaller than those of release at 23°C. The temperature-sensitive release is due to temperature-sensitive swelling ratio. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Highly branched poly(N-isopropylacrylamide) (PNIPAM) has been synthesized by a reversible addition-fragmentation chain transfer (RAFT) copolymerization of NIPAM and a vinyl contained trithiocarbonate RAFT agent. 1H-NMR measurements revealed that the degrees of branch (DB) are in the range of 0.032–0.105. Laser light scattering (LLS) measurements gave the hydrodynamic radii (Rh) of the polymers to be 3.6–5.7 nm with molecular weight in the range of 1.3 × 104 g/mol–2.3 × 10−4 g/mol. Highly branched PNIPAM with terminal thiol groups were obtained by aminolysis the polymers, and the product can be oxidized by air to form disulfide bonds (SS) among chains and resulting in the formation of nanoparticle in aqueous solution. Interestingly, the nanoparticle in size of Rh ˜ 80 nm showed a thermogelling behavior to form bulk hydrogel when the temperature was increased up to 25°C due to the thermo-induced association of the PNIPAM chains among the nanoparticles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Thermoresponsive surface was prepared from commercial poly(vinylidene fluoride) (PVDF) films via surface-initiated atom transfer radical polymerization. The direct initiation of the secondary fluorinated site of PVDF facilitated grafting of the N-isopropylacrylamide (NIPAAm) monomer. The PVDF surfaces grafted with poly(N-isopropylacrylamide) [P(NIPAAm)] were characterized by X-ray photoelectron spectroscopy. Kinetics study revealed that the P(NIPAAm) chain growth from the PVDF surface was consistent with a “controlled” process. The temperature-dependent swelling behavior of the surfaces in aqueous solution was studied by atomic force microscope. At 37°C [above the lower critical solution temperature (LCST, about 32°C) of NIPAAm], the seeded cells adhered and spread on the NIPAAm grafted PVDF surface. Below the LCST, the cells detached from the P(NIPAAm)-grafted PVDF surface spontaneously. The thermoresponsive surfaces are potentially useful as stimuli-responsive adhesion modifiers in the biomedical fields.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The renaturation of lysozyme assisted by a novel type of hairy particles was investigated. The particles used consisted of polystyrene (PS) cores onto which long chains of thermosensitive poly(N-isopropylacrylamide) (PNIPAM) were grafted as shell. Here, two kinds of particles were synthesized as sub-micron PS cores and 89 nm brush thickness (Particle A) and 122 nm brush thickness (Particle B), respectively. Thermosensitive characteristics of the above prepared hairy uniform PS particles with PNIPAM brushes were studied and the results indicated that the lower critical solution temperature (LCST) of PNIPAM brushes grafted on the surface of uniform PS cores was between 33 and 34°C. It was proved that the particles were quite efficient in assisting lysozyme renaturation at high initial protein concentration. When the protein concentration was increased to 500 μg/mL, the refolding yield of the recovery of lysozyme activity could achieve 58.0% (Particle A) and 71.5% (Particle B), compared with only 34.8% by simple dilution refolding. Furthermore, the kinetics of lysozyme refolding in the absence and the presence of the colloidal particles were studied accordingly. The results indicated that the time required for the refolding with colloidal particles was a little bit delayed than that by the simple dilution method owing to the hydrophobic interactions between lysozyme and the PNIPAM brushes. The mechanism of the enhancement for the hairy uniform PS particles with PNIPAM brushes assisted refolding was further discussed. All results above demonstrated that the spherical PNIPAM brushes presented an alternative way to assist protein renaturation in vitro. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114:1270-1277,2009.

To achieve the injectable hydrogel system in order to improve bone regeneration by locally delivering a protein drug including bone morphogenetic proteins, thermo-responsive injectable hydrogels composed of N-isopropylacrylamide (NIPAAm) and vinyl phosphonic acid (VPAc) were prepared. The P(NIPAAm-co-VPAc) hydrogels were also biomineralized by urea-mediation method to create functional polymer hydrogels that deliver the protein drug and mimic the bone extracellular matrix. The loosely cross-linked P(NIPAAm-co-VPAc) hydrogels were pliable and fluid-like at room temperature and could be injected through a small-diameter aperture. The lower critical solution temperature (LCST) of P(NIPAAm-co-VPAc) hydrogel was influenced by the monomer ratio of NIPAAm/VPAc and the hydrogel with a 96/4 molar ratio of NIPAAm/VPAc exhibited an LCST of ∼34.5°C. Water content was influenced by temperature, NIPAAm/VPAc monomer ratio, and biomineralization; however, all hydrogels maintained more than about 77% of the water content even at 37°C. In a cytotoxicity study, the P(NIPAAm-co-VPAc) and biomineralized P(NIPAAm-co-VPAc) hydrogels did not significantly affect cell viability. The loading content of bovine serum albumin in hydrogel, which was used as a model drug, gradually increased with the amount of VPAc in the hydrogel owing to the ionic interaction between VPAc groups and BSA molecules. In addition, the release behavior of BSA from the P(NIPAAm-co-VPAc) hydrogels was mainly influenced by the drug loading content, water content, and biomineralization of the hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A pH- and temperature-responsive semi-interpenetrating copolymer PEG6000/poly(NIPA-co-AMPS) (PEG/AMPS-co-NIPA SIPN), for short PEG SIPN, was made by ammonium persulfate-initiated suspension copolymerization of N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulphonic acid, and N,N′-methylene-bis-acrylamide (MBAA; crosslinker) in the presence of PEG6000. The PEG SIPN copolymer matrices containing nanostructures made in the high-temperature copolymerization resulted in channels for PEG and facile migration of drugs. In drug encapsulation or drug-loading process, one can easily ignore or pay less attention to the interaction between a drug and its encapsulation materials; however, the ignored interactions may induce problems in drug properties or the release behavior in use. Sodium diclofenac (DFNa) precipitates as the carboxylic acid form in an acidic environment, and it is challenging to encapsulate sodium diclofenac in such an acidic matrix without precipitation of the sparingly soluble acid form of DFNa on the surface of the polymer substrate. To avoid bulky precipitation in drug loading, an in situ loading technique was developed for producing gel spheres with DFNa uniformly distributed in the polymer matrix. The technique is based on fast polymerization of spherical droplets of a pregel solution in which the drug is dissolved. Diffusion-loading prodrugs were made in comparison with in situ loading prodrugs in thermal, release kinetics, and release behavior. Drug release profiles (in pH 7.4 phosphate buffer) show that the new drug loading technique gives controlled release during a period of about 7 days at 37°C. By contrast, gel spheres loaded with sodium diclofenac using the conventional diffusion technique produced almost total release of the drug within about 24 h. The thermal stability of sodium diclofenac, the PEG/AMPS-co-NIPA SIPN, and the prodrugs made with the SIPN and sodium diclofenac was studied. A near zero-order release kinetics was found in the in vitro release of sodium diclofenac with in situ loading PEG SIPN prodrug. We have, for the first time, studied sodium diclofenac release behavior from the PEG SIPN hydrogel systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Novel temperature-sensitive poly[N-isopropylacrylamide-co-2-hydroxyethylacrylate] [P(NIPAAm-HEAc)] colloidal crystals containing β-cyclodextrin (β-CD) were prepared. These reversibly tunable supramolecular inclusion complexes display brilliant colors, due to the self-assembly of several structured nanoparticles to form crystal structures. The hydrogels displayed rainbow colors upon the variation of the β-CD concentration and can be made either visible or invisible by simply changing the temperature. The inclusion complexes were characterized using NMR spectroscopy, laser light scattering, UV-visible spectroscopy, and viscometer measurements. Compared with the conventional poly(N-isopropylacrylamide) gel, the β-CD-incorporated hydrogels in aqueous solution showed a lower critical solution temperature of about 57°C, which can be attributed to the hydrogen bonding between P(NIPAAm-HEAc) included in β-CD and water, which is enhanced by the hydrophilic groups of β-CD. The use of these materials as drug carriers was also evaluated by making use of their thermo-responsive behavior. The release time of a model drug, 5-fluorouracil (5-FU), from the novel inclusion complexes was prolonged in comparison to that from P(NIPAAm-HEAc) without β-CD. The significance of the present drug delivery system is the mixing of the gel and drug without any chemical reaction at room temperature, resulting in a gelled drug depot for slow and controlled release.

Self-assembly of thermo-sensitive poly (t-butyl acrylate)-b-poly(N-isopropylacrylamide) (PtBA- b-PNIPAM) micelles in aqueous medium and its applications in controlled release of hydrophobic drugs were described. PtBA-b-PNIPAM was synthesized by atom transfer radical polymerization and aggregated into thermo-sensitive core-shell micelles with regular spheres in water, which was confirmed by 1H-NMR, fluorescence spectroscopy, transmission electron microscopic (TEM), and UV–vis spectroscopic techniques. The critical micelle concentration of micelles decreased with the increase of the hydrophobic components. The anti-inflammation drug naproxen (NAP) was loaded as the model drug into polymeric micelles, which showed a dramatic thermo-sensitive fast/slow switching behavior around the lower critical solution temperature (LCST). When the temperature was enhanced above LCST, release of NAP from core-shell micelles was accelerated ascribed to the temperature-induced deformation of micelles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

In this work, the degree of crosslinking on the volumetric contraction–expansion processes of hydrogels made of poly(N-isopropylacrylamide) (NIPA) (initial amount: Cm) with varied amount (z) of crosslinking agent methylene-bis-acrylamide (BIS) in reference to most commonly used NIPA gel that was synthesized with Cm = 700 mM and z = 8.6 mM was investigated by applying our recently developed pycnometry. We focused on characteristic role of four polymeric NIPA residues directly bonded to a single BIS molecule by evaluating the total volume of gels per four NIPA residues directly bonded to a BIS molecule, plus associated water [νsp(gel)(NIPA)bonded)(T)], and the corresponding number of water molecules per four NIPA residues [Ns(gel)(NIPA)bonded)(T)]. We elucidated how these quantities characteristically contribute to changes in the volumetric contraction–expansion processes of hydrogels. A comparison of these quantities with the corresponding quantities for (NIPA)unbonded residues clearly revealed a significant structural difference between (NIPA)bonded and (NIPA)unbonded. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009