Temperature‐induced volume change and glucose sensitivity of poly[(N‐isopropylacry‐ lamide)‐co‐acrylamide‐co‐(phenylboronic acid)] microgels

Nearly monodisperse glucose‐sensitive poly[(N‐isopropylacrylamide)‐co‐acrylamide‐co‐(phenylboronic acid)] microgels were synthesized in aqueous media by the functionalization of poly[(N‐isopropylacrylamide)‐co‐acrylamide‐co‐(acrylic acid)] microgels with 3‐aminophenylboronic acid via carbodiimide coupling. The glucose‐sensitive and thermosensitive behaviour of the microgels was investigated using a dynamic light scattering technique. The introduction of the hydrophobic phenylboronic acid (PBA) group significantly decreases the temperature at which maximum volume change of the resultant microgel particles is observed. The glucose sensitivity of the PBA‐containing microgels relies on the stabilization of the charged phenylborate ions by binding with glucose, which can convert more hydrophobic PBA groups to the hydrophilic phenylborate ions. The effect of pH, ionic strength and PBA content on temperature‐induced volume change and glucose sensitivity was systemically studied. The effect of NaCl on the glucose sensitivity was also investigated at physiological pH and ionic strength. Copyright © 2011 Society of Chemical Industry     

Thermo‐ and pH‐responsive microgels for controlled release of insulin

Microgel particles were prepared, made of hydroxypropylcellulose‐graft‐(acrylic acid) (HPC‐g‐AA) and acrylic acid(AA). The particles undergo reversible volume phase transitions in response to both pH and temperature changes while keeping the inherent properties of PAA and HPC‐g‐AA. Dynamic light scattering measurements reveal that the average hydrodynamic radius and hydrodynamic radius distributions of the microgel particles depend on temperature and pH. The microgels exhibit excellent pH sensitivity and a higher swelling ratio at higher pH in aqueous solution. In vitro release study shows that the amount of insulin released from the microgels is less at pH = 1.2 than at pH = 6.8. The results indicate that the resultant microgels seem to be of great potential for intelligent oral drug delivery. Copyright © 2012 Society of Chemical Industry     

Synthesis and characterization of novel,temperature‐sensitive microgels based on N‐isopropylacrylamide and tert‐butyl acrylate

A series of temperature‐sensitive microgels based on N‐isopropylacrylamide as the main monomer, tert‐butyl acrylate (tBA) as the comonomer, and N,N′‐methylene‐bis(acrylamide) as the crosslinker were synthesized with a modified surfactant‐free emulsion polymerization method. The chemical structure and global shape with an excellent monodispersity of the microgels were confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The temperature‐sensitive behavior of the microgels was investigated by dynamic light scattering and ultraviolet–visible spectrophotometric analysis. The results show that the volume phase‐transition temperature of the poly(N‐isopropylacrylamide‐co‐tert‐butyl acrylate) [poly(NIPAM‐co‐tBA)] microgels were tuned over a broad range by the incorporated amount of tBA comonomer and their temperature sensitivity decreased with increasing content of tBA units incorporated into the microgel network. Furthermore, the swelling ratios of the poly (NIPAM‐co‐tBA) microgels were lowered gradually with increasing tBA unit content within the microgel network. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2962–2967, 2007     

Multi‐responsive microgel of a water‐soluble monomer via emulsion polymerization

Microgel of a water‐soluble monomer [2‐(N‐morpholino)ethyl methacrylate (MEMA)] was successfully prepared in aqueous media via emulsion polymerization by using a novel water‐soluble block copolymer as stabilizer. Characterization studies confirmed monodisperse spherical morphologies of microgels with a diameter of 280 nm at neutral pH. These microgels exhibited multi‐responsive behavior by responding solution pH, temperature, ionic strength, type of dispersing media, and magnetic particles. It swells well at low pH (<6.0) and at low temperature, but shrinks above pH 6.0, or even more shrinks with salt addition at neutral and basic conditions. In addition, the hydrodynamic diameter of PMEMA microgel was decreased gradually at basic and neutral pH when solution temperature was increased up to the lower critical solution temperature of PMEMA (LCST, 35°C), but microgel diameter did not change much above LCST. Multi‐responsive behavior of PMEMA microgel was investigated by using dynamic light scattering, UV‐Vis spectrophotometer and zeta potentiometer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42072.     

Preparation and thermal response behavior of poly(N‐isopropylacrylamide‐co‐a crylic acid) microgels via soap‐free emulsion polymerization based on AIBN initiator

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 ¹H‐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. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of ethyl methacrylate content on the volume‐phase transition of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] microgels

A novel series of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] (p(NIPAM‐co‐EMA)) microgels was prepared by the surfactant‐free radical polymerization of N‐isopropylacrylamide (NIPAM) with ethyl methacrylate (EMA). The shape, size dispersity and volume‐phase transition behavior of the microgels were investigated by transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, dynamic light scattering (DLS) and differential scanning calorimetry (DSC). The transmission electron micrographs and DLS results showed that microgels with narrow distributions were prepared. It was shown from UV–Vis, DLS and DSC measurements that the volume‐phase transition temperature (VPTT) of the p(NIPAM‐co‐EMA) microgels decreased with increasing incorporation of EMA, but the temperature‐sensitivity was impaired when more EMA was incorporated, causing the volume‐phase transition of the microgels to become more continuous. It is noteworthy that incorporation of moderate amounts of EMA could not only lower the VPTT but also enhance the temperature‐sensitivity of the microgels. The reason for this phenomenon could be attributed to changes in the complicated interactions between the various molecules. Copyright © 2004 Society of Chemical Industry     

Emulsifier‐free poly[2‐(diethylamino)ethyl methacrylate] microgels with cationic quaternary ammonium monomers

Although poly[2‐(diethylamino)ethyl methacrylate] (PDEA) microgels are biocompatible and show potential in drug delivery, little research exists with respect to their preparation. Therefore, emulsifier‐free PDEA microgels were synthesized in the presence of cationic ammonium salts of 2‐(dimethylamino)ethyl methacrylate (DMA) that were quaternized with 1‐bromohexadecane, 1‐bromooctadecane, 1‐bromopentane, or benzyl chloride. These served as both comonomers and polymerizable surfactants, providing colloidal stability to the DEA droplets during polymerization. The stability of the microgel particles in different pH values between 4 and 11 was investigated by turbidity–wavelength measurements. The benzyl group containing monomer was the most stabilizing. The pH‐responsive behavior of the microgels in dilute aqueous solution was examined with respect to the amount of DEA, amount of copolymer, type of copolymer, and water content. Most of the microgels remain colloidally stable up to a pH of 9.0, while particles are less than 300 nm in size at pH 8.0. The isoelectric points of the microgels are higher than 8.5 in most cases. In fact, this value exceeds 12.0 by modifying the amount of copolymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43196.     

Dually responsive multinetworked hydrogels with improved performances by covalently bonding poly(N‐isopropylacrylamide)‐based microgels and poly(vinyl alcohol) skeleton

To prepare intelligent hydrogels with both good mechanical performance and fast response, a series of multinetworked composite hydrogels with pH and thermo‐responsivity were designed and fabricated combining the advantages of both interpenetrating polymer network hydrogels and microgels. To begin with, precipitation polymerization of N‐isopropylacrylamide, methacrylic acid and polyethyleneglycol methacrylate was carried out in poly(vinyl alcohol) (PVA) aqueous solution, yielding thermo‐ and pH‐responsive copolymeric microgels. Then glutaraldehyde was added to the obtained microgel dispersion to covalently bond the microgel particles and PVA through acetal reaction, leading to the formation of multinetworked hydrogels with dual responses. The morphology of microgels and the internal microstructure of composite hydrogels were characterized by transmission electron microscope and scanning electron microscope, respectively. The influence of the PVA content and glutaraldehyde dosage on the mechanical behavior of the prepared hydrogels was investigated by means of uniaxial compressive tests. Experimental results reveal that the as‐prepared composite hydrogels exhibit enhanced mechanical performance compared to conventional hydrogels. Investigation onthe swelling and deswelling behaviors shows that they possess good temperature‐ and pH‐sensitivity andswell/deswell more rapidly than conventional hydrogels. POLYM. COMPOS., 2012. © 2013 Society of Plastics Engineers     

Preparation of novel amphiphilic copolymer microspheres and their drug‐release and glucose‐sensitive properties

A novel amphiphilic copolymer was prepared by the copolymerization of N‐acryloyl‐3‐aminophenylboronic acid with β‐cyclodextrin containing maleic anhydride. The copolymer was fully characterized with ¹³C‐NMR, ¹H‐NMR, IR, and scanning electron microscopy. The self‐assembling mechanism of the copolymer in H₂O–CH₃OH cosolvents was studied. Gliclazide as a model drug was loaded inside the copolymer microspheres, and the drug‐release behavior of the microspheres was studied. The results of in vitro oscillating release tests indicated that the microspheres responded to glucose rapidly in 30 min, and the microspheres exhibited self‐regulated on–off release behavior four to six times in 6 h between the solution with 3 g/L glucose and the medium without glucose; this met the clinical requirements of multidrug delivery. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermochromic microgels and core‐shell microgels based on fluorescence resonance energy transfer

Microgels exhibiting thermochromic behavior based on fluorescence resonance energy transfer (FRET) are prepared. The FRET microgels consist of poly(N‐isopropylacrylamide) (PNiPAm) networks with fixed fluorescein and rhodamine moieties and exhibits volume phase transition (VPT) at 34–35°C. A critical decrease in their sizes during the VPT enhances the efficiency of FRET between fluorescein as a donor and rhodamine as an acceptor. Therefore, emission from fluorescein (523 nm) and that of rhodamine (579 nm) is dominant at temperatures below and above the VPT temperature, respectively, when fluorescein is excited. We also prepare thermochromic core‐shell FRET microgel exhibiting two‐step color change. The microgels consist of a PNiPAm core and a poly(N‐isopropylacrylamide‐co‐N,N‐diethylacrylamide) shell and exhibit dual temperate‐responsiveness at 19 and 33°C. The fluorescence spectrum of the microgels also changes in two steps at these temperatures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of microgel content and n‐methylolacrylamide on the properties of microgel composite hydrogels prepared by postcrosslinking method

Acrylamide co 2‐acrylamido‐2‐methylpropane sulfonic acid microgel composite (MC) hydrogels were prepared by heating MC polymer with 50% water content. Crosslinking reaction occurred in the heating process and reactive microgels with hydroxymethyl groups introduced by N‐methylolacrylamide (NMA) were used as postcrosslinkers. Microgel swollen size is influenced by NMA content. Both microgel and its NMA content affect MC hydrogel properties, which relates to the crosslinking chain length and the crosslinking density. The tensile strength of MC hydrogels increases and their elongation decreases as the microgel content increases from 0.1 to 0.5 g. Both the tensile strength and the elongation decrease as the microgel content further increases from 0.5 to 1.1 g. The MC hydrogel tensile strength increases and the elongation decreases as the NMA content of microgels increases from 5.0 to 14.8%. However, they both decrease when the NMA content of microgels exceeds 14.8%. Although the crosslinking chains υ calculated from tensile stress–strain curves were very high, MC hydrogels were elastic and had the highest tensile strength of 127 kPa and considerably moderate elongation of 427%. Their excellent mechanical properties attributed to their unique structure crosslinked by microgel particles. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Thermosensitive phase transition kinetics of poly(N‐isopropylacryl amide‐co‐acrylamide) microgel aqueous dispersions

Thermosensitive poly(N‐isopropylacrylamide‐co‐acrylamide) microgel particles were prepared through precipitation polymerization. The diameters of the microgel particles were in the range of 220–270 nm and showed a monodispersion. The lower critical solution temperatures (LCST) of the microgel dispersions were measured by dynamic light scattering and turbidimetric analysis. The results indicated that the LCST increased with an increase of acrylamide (AAm) content in the copolymer composition. The kinetics of the thermosensitive phase transitions of the microgel particles were investigated by time‐course UV–vis spectroscopy. The results indicated that the higher the content of AAm in copolymer composition, the more time is required for equilibrium deswelling and the less time required for equilibrium swelling. In addition, the time required for equilibrium deswelling decreased with an increase of the content of the microgel particles in dispersions. By contrast, the time required for equilibrium swelling increased slightly. Thus, a suitable LCST and time required for equilibrium of phase transition can be achieved by adjusting the molar ratio of the comonomers in the microgels and the content of the microgel particles in dispersions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dendrimer‐encapsulated Pt nanoparticles/polyaniline nanofibers for glucose detection

A novel amperometric glucose biosensor based on self‐assembling glucose oxidase (GOx) and dendrimer‐encapsulated Pt nanoparticles (Pt‐DENs) on nanofibrous polyaniline (PANI) was described. PANI nanofibers were synthesized via an interfacial polymerization method. A sulfonated polyelectrolytes‐poly(sodium 4‐styrenesulfonate) (PSS) was used to form the negative PANI/sulfonated polyelectrolyte complex, which had good disperse in aqueous solution. GOx was immobilized on the PANI/PSS surface by alternatively assembling a cationic Pt‐DENs layer and an anionic GOx layer. The unique sandwich‐like layer structure (Pt‐DENs/GOx/Pt‐DENs/PANI/PSS) formed by self‐assembling provides a favorable microenvironment to keep the bioactivity of GOx and to prevent enzyme molecule leakage. The fabricated Pt‐DENs/GOx/Pt‐DENs/PANI/PSS electrode exhibited excellent response performance to glucose with a detection limit of 0.5 μM, wide linear range from 10 μM to 4.5 mM, short response time within 5 s, improved sensitivity of 39.63 μA/(mM cm²), and good stability (85% remains after 20 days). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electric‐field‐induced layer‐by‐layer fabrication of stable second‐order nonlinear optical films

BACKGROUND: Second‐order nonlinear optical (NLO) films have been made using electric field poling polymer and Langmuir–Blodgett techniques with non‐centrosymmetric structures that exhibit relatively high values of nonlinear susceptibility (χ²), but the shortcomings of insufficient temporal or mechanical stability have restricted their potential applications. In this study, electric‐field‐induced layer‐by‐layer assembly was investigated as an effective technique to prepare low molecular weight chromophoric (LMWC) molecules of high degree of self‐ordering and density in NLO films. RESULTS: A new and stable LMWC molecule, 2‐({4‐[4‐(2‐carboxy‐2‐cyanovinyl)‐Z‐phenylazo]‐phenyl}‐methylamino)‐ethyl acid (DRCB), was first designed and synthesized successfully. The chromophore possesses two negative groups, one at each end, and still retains molecular polarity after ionization. DRCB was successfully assembled with polycationic diazoresin using the electric‐field‐induced layer‐by‐layer assembly method to construct stable organic second‐order NLO multilayer films. Upon UV irradiation, the interaction between multilayers was converted from an electrostatic interaction to covalent bonds. CONCLUSION: Due to the DC electric field effect in the assembly process, in addition to introducing the stable chromophore molecule and the covalent crosslinking structure in the films, the second‐order NLO films fabricated using the method described have large second harmonic generation response, good thermal stability and excellent chemical stability, which offer potential advantages for device applications. Copyright © 2009 Society of Chemical Industry     

Alternative procedure for the incorporation of quantum dots into poly(N‐isopropyl acrylamide‐co‐acrylic acid) microgels based on multiple interactions

Monodisperse fluorescent poly(N‐isopropyl acrylamide‐co‐acrylic acid) microgels doped with quantum dots (QDs) were fabricated as follows. First, cysteamine‐capped cadmium telluride (CA–CdTe) QDs were introduced into the microgels at pH 7 by electrostatic interactions. Afterward, the CA–CdTe QDs were further immobilized in the microgels by the collapse of the polymer network when the pH of solution was adjusted to 4. In this system, there existed multiple interactions between the CA–CdTe QDs and the microgels, including hydrogen bonds, electrostatic interactions, and coordination bonds. The photoluminescence intensity and maximum emission wavelength of the resulting microgels could be easily adjusted by changes in the content of the CA–CdTe QDs in the hybrid microgels (HMs) and with differently sized QDs, respectively. We found that the lower the addition of CA–CdTe QDs was, the bigger the blueshift of the photoluminescence spectra of the HMs was and the weaker the photoluminescence intensity was. Finally, temperature‐responsive emission of the HMs was examined. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43227.     

Room temperature preparation of highly crosslinked microgels

A series of highly crosslinked microgels has been prepared at room temperature via photoinitiated polymerisation in dilute solution using methyl methacrylate (MMA) and ethylene dimethacrylate (EDMA), respectively as non-functional monomer and crosslinker in N,N-dimethylformamide (DMF) as a solvent. The effect of monomer concentration and EDMA/MMA ratio on the yield, molecular weight and microgel size was studied and the data were compared to those previously obtained for microgels of similar composition prepared by thermal initiation. This mild polymerisation method yields better results compared to the more conventional thermal method, since it allows higher monomer concentrations to be employed as well as a better microgel size control. Consequently, the method can be advantageously used for the preparation of highly crosslinked microgels with improved properties, particularly useful, e.g. for molecular imprinting applications.     

Rheological study on the thermoinduced gelation behavior of poly(N‐isopropylacrylamide‐co‐acrylic acid) microgel suspensions

Submicron‐sized thermoresponsive poly(N ‐isopropylacrylamide‐co ‐acrylic acid) microgels were synthesized by soap‐free emulsion polymerization. The physical state of the microgel suspensions, in a wide range of polymer concentrations (1.1–7.1 wt %), transformed from fluid to gel when the temperature was elevated across their volume phase transition temperature at pH = 3.0. Such thermoinduced gelation behavior was studied in detail by small‐deformation oscillatory rheological measurements within the linear viscoelastic region. It was found that the gelation temperature was strongly affected by the polymer concentration, decreasing as the polymer concentration increased. The gelation kinetics showed that the suspension gelled more quickly at either larger polymer concentration or higher isothermal heating temperature. In an isothermal frequency sweep for the as‐formed gels, both storage and loss moduli, G′ and G″ , exhibited a power‐law behavior, that is, G′ (ω) ～ ω^0.2–0.4 and G″ (ω) ～ ω^0.46?0.50 within the frequency range where G′ dominates G″ . In addition, the elasticity of the gels, which results from the attractive particle bonds, increased markedly with increasing polymer concentration. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45259.     

Surface‐active amphiphilic poly[(2‐acrylamido‐2‐methylpropanesulfonic acid)‐co‐(N‐isopropylacrylamide)] nanoparticles as stabilizer in aqueous emulsion polymerization

This work reports the effect of nanogel solid particles on the surface and interfacial tension of water/air and water/styrene interfaces. Moreover, the work aimed to use nanogels as a stabilizer for miniemulsion aqueous polymerization. A series of amphiphilic crosslinked N‐isopropylacrylamide (NIPAm) and 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) copolymer nanogels were synthesized based on an aqueous copolymerization batch method. Divinylbenzene and N,N‐methylene bisacrylamide were used as crosslinkers. The morphologies of the prepared nanogels were investigated using transmission and scanning electron microscopies. The lower critical transition temperatures were determined using differential scanning calorimetry. The surface tension of colloidal NIPAm/AMPS dispersions was measured as functions of surface age, temperature and the morphology of the NIPAm/AMPS nanogels. The NIPAm/AMPS nanogels reduced the surface tension of water to about 30.1 mN m^?1 at 298 K with a small increase at 313 K. Surface activities of these nanogels in water were determined by surface tension measurements. The NIPAm/AMPS dispersions had high surface activity and were used as a stabilizer to prepare a crosslinked poly(styrene‐co‐AMPS) microgel based on emulsion crosslinking polymerization. © 2013 Society of Chemical Industry     

Synthesis,Crystal Structure,and Thermal Behaviors of 3‐Nitro‐1,5‐bis(4,4′‐dimethylazide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP)

The energetic material, 3‐nitro‐1,5‐bis(4,4′‐dimethyl azide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP), was firstly synthesized by means of Click Chemistry using 1,5‐diazido‐3‐nitrazapentane as main material. The structure of NDTAP was confirmed by IR, ¹H NMR, and ¹³C NMR spectroscopy; mass spectrometry, and elemental analysis. The crystal structure of NDTAP was determined by X‐ray diffraction. It belongs to monoclinic system, space group C2/c with crystal parameters a=1.7285(8) nm, b=0.6061(3) nm, c=1.6712(8) nm, β=104.846(8)°, V=1.6924(13) nm³, Z=8, μ=0.109 mm⁻¹, F(000)=752, and D_c=1.422 g cm⁻³. The thermal behavior and non‐isothermal decomposition kinetics of NDTAP were studied with DSC and TG‐DTG methods. The self‐accelerating decomposition temperature and critical temperature of thermal explosion are 195.5 and 208.2 °C, respectively. NDTAP presents good thermal stability and is insensitive.     

Highly transparent thermoresponsive surfaces based on tea‐stain‐inspired chemistry

A highly transparent thermoresponsive surface that could switch its wettability at different temperatures was constructed via tea‐stain‐inspired chemistry. The pristine tannic acid was modified by alkyl bromide with a substitution degree of 1.7 alkyl bromide units per tannic acid molecule. A coating of the alkyl bromine modified tannic acid with a thickness of 22 ± 3 nm was deposited onto the surface of glass via auto‐oxidation. A poly(N‐isopropylacrylamide) (PNIPAAm) brush was grafted from the alkyl bromide initiator via surface initiation atom transfer radical polymerization with a polymer grafting density of 8.6 × 10^?3 mg/cm². Due to the low thickness of the tannic acid and PNIPAAm coating, the transparency of this thermoresponsive surface remained constant at 94.3% even when the temperature was changed from 20 to 40 °C, but the water contact angle of this surface increased rapidly when the temperature was elevated from 25 to 35 °C. Due to the inevitable hydrolysis and deprotonation, this tea‐stain‐inspired chemistry‐based coating was stable in aqueous solution with a pH of 7 or isopropanol for soaking times of up to 24 h. The coating reported here may have various potential applications such as surfaces for cell culture media, food storage, or self‐cleaning materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46694.