Analysis and retention behavior of isoflavone glycosides and aglycones in Radix Astragali by HPLC with hydroxypropyl‐β‐cyclodextrin as a mobile phase additive

In order to determine isoflavone glycosides (calycosin‐7‐O‐β‐d ‐glucoside and formononetin‐7‐O‐β‐d ‐glucoside) and aglycones (calycosin and formononetin), a simple HPLC method with isocratic elution employing hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as a mobile phase additive was developed. Various factors affecting the retention of isoflavone glycosides and aglycones in the C₁₈ reversed‐phase column, such as the nature of cyclodextrins, HP‐β‐CD concentration, and methanol concentration, were systematically studied. The results show that HP‐β‐CD, as a very effective mobile phase additive, can markedly reduce the retention of isoflavone glycosides and aglycones, and the decrease magnitudes of isoflavone aglycones are more than those of their glycosides. The role of HP‐β‐CD in the developed HPLC method is attributed to the formation of the inclusion complexes between isoflavone glycosides (or aglycones) and HP‐β‐CD. So, the apparent formation constants of the isoflavone glycosides (or aglycones)/HP‐β‐CD inclusion complexes also were investigated. Isoflavone glycosides (and aglycones) form the 1:1 inclusion complexes with HP‐β‐CD, and the isoflavone aglycones/HP‐β‐CD complexes are more stable than the isoflavone glycosides/HP‐β‐CD complexes. Finally, the optimized method was successfully applied for the determination of isoflavone glycosides and aglycones in Radix Astragali samples.     

Thermo‐ and pH‐induced phase transitions and network parameters of poly(N‐isopropylacrylamide‐ co‐2‐acrylamido‐2‐methyl‐propanosulfonic acid) hydrogels

Dual temperature‐ and pH‐sensitive hydrogels composed of N‐isopropylacrylamide (NIPAM) and 2‐acrylamido‐2‐methyl‐propanosulfonic acid (AMPS) were prepared by free‐radical crosslinking copolymerization in aqueous solution at 22 °C. The mole percent of AMPS in the comonomer feed was varied between 0.0 and 7.5, while the crosslinker ratio was fixed at 5.0/100. The effect of AMPS content on thermo‐ and pH‐ induced phase transitions as well as equilibrium swelling/deswelling, interior morphology and network structure was investigated. The volume phase transition temperature (VPT‐T) was determined by both swelling/deswelling measurements and differential scanning calorimetry (DSC) technique. In addition, the volume phase transition pH (VPT‐pH) was detected from the derivative of the curves of the swelling ratio (dQ_v/dpH) versus pH. The polymer‐solvent interaction parameter (χ) and the average molecular mass between crosslinks ( ) of hydrogels were calculated from swelling ratios in buffer solutions at various pHs. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter of hydrogels were also determined by using the modified Flory–Rehner equation. The negative values for ΔH and ΔS indicated that the hydrogels had a negative temperature‐sensitive property in water, that is, swelling at a lower temperature and shrinking at a higher temperature. It was observed that the experimental swelling data of hydrogels at different temperature agreed with the modified Flory‐Rehner approach based on the affine network model. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1713–1724, 2008     

Synthesis and thermal properties of a novel lactose‐containing poly(N‐isopropylacrylamide‐co‐acrylamidolactamine) hydrogel

An improved, simple, and efficient method for the synthesis of lactose‐containing monomer acrylamidolactamine (LAM) has been reported. Free radical copolymerization of this monomer with N‐isopropylacrylamide (NIPAM) in the presence of the crosslinking reagent N,N′‐methylenebisacrylamide (BisA) (1.2 mol %) proceeded smoothly in an aqueous solution using potassium persulfate (KPS) and N,N,N′,N′‐tetramethylethylenediamine (TMEDA) as the initiating system and gave transparent hydrogels. Reactivity ratios were estimated from copolymerization reactions carried out in solution without BisA crosslinker and at low conversion, by using both linearization and nonlinearization methods. They were found to be r_LAM = 0.75 and r_NIPAM = 1.22. The swelling behavior of the hydrogels was studied by immersion of the hydrogels in deionized water at different temperatures. Equilibrium water uptake was increased when the LAM content was higher than 47 mol %, and reached ≈ 44‐fold with 100 mol % LAM at room temperature. Depending on the composition, the gels showed sharp swelling transitions with small changes in temperature. Differential scanning calorimetry (DSC) was used to characterize the swelling transition and the organization of water in the copolymer hydrogels. The amounts of freezable water in these hydrogels ranged from 81 to 89%, and was not correlated to the content of the sugar monomer. These gels have potential applications as biocompatible materials. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1393–1402, 1999     

Organic–inorganic hybrid hydrogels involving poly(N‐isopropylacrylamide) and polyhedral oligomeric silsesquioxane: Preparation and rapid thermoresponsive properties

3‐Acryloxypropylhepta(3,3,3‐trifluoropropyl) polyhedral oligomeric silsesquioxane (POSS) was synthesized and used as a modifier to improve the thermal response rates of poly(N‐isopropylacrylamide) (PNIPAM) hydrogel. The radical copolymerization among N‐isopropylacrylamide (NIPAM), the POSS macromer and N,N′‐methylenebisacrylamide was performed to prepare the POSS‐containing PNIPAM cross‐linked networks. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) showed that the POSS‐containing PNIPAM networks displayed the enhanced glass transition temperatures (T_g's) and improved thermal stability when compared with plain PNIPAM network. The POSS‐containing PNIPAM hydrogels exhibited temperature‐responsive behavior as the plain PNIPAM hydrogels. It is noted that with the moderate contents of POSS, the POSS‐containing PNIPAM hydrogels displayed much faster response rates in terms of swelling, deswelling, and re‐swelling experiments than plain PNIPAM hydrogel. The improved thermoresponsive properties of hydrogels have been interpreted on the basis of the formation of the specific microphase‐separated morphology in the hydrogels, that is, the POSS structural units in the hybrid hydrogels were self‐assembled into the highly hydrophobic nanodomains, which behave as the microporogens and promote the contact of PNIPAM chains and water. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 504–516, 2009     

Synthesis and characterization of a poly(N‐isopropylacrylamide) with β‐cyclodextrin as pendant groups

A novel linear poly(N‐isopropylacrylamide) (PNIPA) with β‐cylodextrin (β‐CD) moiety (PNIPA‐β‐CD) was synthesized by the conjugation of β‐CD carrying amino groups (EDA‐β‐CD) onto PNIPA with epoxy groups (P(NIPA‐co‐GMA), M_n = 3.86 × 10⁴), and the related reaction conditions are investigated. PNIPA‐β‐CD was characterized by means of IR, NMR and UV spectroscopes, element analysis, and differential scanning calorimetry (DSC). The number‐average molecular weight (M_n) and the β‐CD content of the obtained PNIPA‐β‐CD are 4.87 × 10⁴ and 18.8 wt %, respectively. PNIPA‐β‐CD can not only respond to temperature stimuli but also include guest molecules. Lower critical solution temperature (LCST) of aqueous PNIPA‐β‐CD solution is similar to that of PNIPA. The association constant (K_a) for PNIPA‐β‐CD with methyl orange (MO) is 2.4 × 10³ L mol^?1 at pH 1.4, which is comparable to that of EDA‐β‐CD (K_a = 2.9 × 10³ L mol^?1). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3516–3524, 2005     

Veronicafolin－β-环糊精的物化表征及Veronicafolin－羟丙基-β-环糊精包合物溶解性的增强

用氢谱、红外光谱、X-射线粉末衍射、热分析、元素分析等测试方法研究了Veronicafolin (3,5,4′-三羟基-6,7,3′-三甲氧基黄酮) 和β-环糊精 (β-CD) 的固体包合物的谱学特征。元素分析结果显示形成Veronicafolin-β-CD·20H2O包合物，其中C：39.58%, H: 5.75%，表明包合物中主客体比为1∶1。该包合类型属于A_L-型。通过紫外-可见分光光度法研究了在羟丙基-β-环糊精（HP-β-CD）的存在下Veronicafolin的相溶解度曲线，测得校正曲线为y = 24148x + 0.0075 (r=0.9999)，相溶解曲线为y=0.4738x-2.0×10^-7 (r=0.9490)，包结平衡常数Ks为4.5×10⁶mol-1。HP-β-CD提高了黄酮醇Veronicafolin的溶解度。     

High‐pressure NMR characterization of triacetyl‐β‐cyclodextrin in supercritical carbon dioxide

Cyclodextrins are used in many drug formulations since their cavities provide microenvironments where drug molecules can enter and form inclusion complexes for controlled drug delivery. Supercritical carbon dioxide (scCO₂) is an alternative to organic solvents and a very attractive medium for the preparation of these inclusion complexes. The potential ability of triacetyl‐β‐cyclodextrin (TA‐β‐CD) to form inclusion complexes in addition to its high miscibility in liquid and scCO₂ could offer a chance for an economical and environmental friendly chemical processing. In this work, high‐pressure NMR studies were performed in order to obtain information on the molecular structure and dynamics of TA‐β‐CD in scCO₂ at 313.15 K and 20 MPa and its ability to form inclusion complexes under these conditions was studied. The influence of scCO₂ on a number of NMR spectral parameters, such as chemical shifts, spin‐spin coupling constants, nuclear Overhauser effect (NOE) and spin‐lattice relaxation (T₁) has been studied. We unequivocally show for the first time structural changes of TA‐β‐CD in scCO₂, like acetyl chain orientation and overall shape distortions that can affect its inclusion capability in this medium. The possibility of cavity self‐closure is discussed and the results of two inclusion studies that support cavity self‐closure, with the angiotensin‐converting enzyme inhibitor, captopril, and the nonsteroid anti‐inflammatory drug, flufenamic acid, are presented. Copyright © 2008 John Wiley & Sons, Ltd.     

A mixed cyclodextrin‐biphenyl thermotropic liquid crystal: Synthesis,liquid‐crystalline properties,and supramolecular organization

A well‐defined structure liquid crystal heptakis [6‐deoxy‐6‐(1‐H‐1,2,3‐triazol‐4‐yl)(methyl)6‐(4‐methoxybiphenyl‐4′‐yloxy) hexanoyl]‐β‐cyclodextrin (H6B‐β‐CD) was synthesized from propargyl 6‐(4‐methoxybiphenyl‐4′‐yloxy) hexanoate (P6B) and heptakis (6‐deoxy‐6‐azido)‐β‐cyclodextrin ((N₃)₇‐β‐CD) by click reaction. The chemical structure of H6B‐β‐CD was confirmed by ¹H NMR, FTIR, and MALDI‐TOF MS. The thermal stability of the compound was investigated by thermogravimetric analysis (TGA). The liquid crystalline behavior was studied by differential scanning calorimetry (DSC), polarizing optical microcopy (POM), and wide‐angle X‐ray diffraction (WAXD) measurement. These investigations have shown that the supramolecular structure of H6B‐β‐CD are consisted of a large scale ordered lamellar structure and a small scale ordered structure (SmE) at low temperature region. As the temperature increases, the small scale structure becomes disordered relatively in the first instance, from smectic E to smectic A. Then, the lamellar structure collapses and nematic phase and isotropic phase are observed in sequence. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2838–2845, 2010     

Synthesis and Characterization of pH‐sensitive Poly(IA‐co‐AAc‐co‐AAm) Hydrogels via Frontal Polymerization

In this work, we report a series of poly(itaconic acid‐co‐acrylic acid‐co‐acrylamide) (poly(IA‐co‐AAc‐co‐AAm)) hydrogels via frontal polymerization (FP). FP starts on the top of the reaction mixture with aid of heating provided from soldering iron gun. Once polymerization initiated, no further energy is required to complete the process. The influences of IA/AAc weight ratios on frontal velocities, temperatures, and conversions on the reaction time are thoroughly investigated and discussed where the amount of AAm monomer remains constant. Fourier transform‐infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscope (SEM), dynamic mechanical analysis, and the swelling measurement are applied to characterize the as‐synthesized poly(IA‐co‐AAc‐co‐AAm) hydrogels. Interestingly, the swelling ratios of the hydrogels are changed with different IA/AAc contents, and the maximum swelling ratios are ~4439% in water. SEM images describe highly porous morphologies and explain good swelling capabilities. Moreover, the poly(IA‐co‐AAc‐co‐AAm) hydrogels exhibit superior pH‐responsive ability. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2214–2221     

Facile preparation of core‐crosslinked micelles from azide‐containing thermoresponsive double hydrophilic diblock copolymer via click chemistry

Double hydrophilic diblock copolymer, poly(N,N‐dimethylacrylamide)‐b‐poly(N‐isopropylacrylamide‐co‐3‐azidopropylacrylamide) (PDMA‐b‐P(NIPAM‐co‐AzPAM), containing azide moieties in one of the blocks was synthesized via consecutive reversible addition‐fragmentation chain transfer polymerization. The obtained diblock copolymer molecularly dissolves in aqueous solution at room temperature, and can further supramolecularly self‐assemble into core‐shell nanoparticles consisting of thermoresponsive P(NIPAM‐co‐AzPAM) cores and water‐soluble PDMA coronas above the lower critical solution temperature of P(NIPAM‐co‐AzPAM) block. As the micelle cores contain reactive azide residues, core crosslinking can be facilely achieved upon addition of difunctional propargyl ether via click chemistry. In an alternate approach in which the PDMA‐b‐P(NIPAM‐co‐AzPAM) diblock copolymer was dissolved in a common organic solvent (DMF), the core‐crosslinked (CCL) micelles can be fabricated via “click” crosslinking upon addition of propargyl ether and subsequent dialysis against water. CCL micelles prepared by the latter approach typically possess larger sizes and broader size distributions, compared with that obtained by the former one. In both cases, the obtained (CCL) micelles possess thermoresponsive cores, and the swelling/shrinking of which can be finely tuned with temperature, rendering them as excellent candidates as intelligent drug nanocarriers. Because of the high efficiency and quite mild conditions of click reactions, we expect that this strategy can be generalized for the structural fixation of other self‐assembled nanostructures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 860–871, 2008     

Synthesis,swelling properties,and network structure of new stimuli‐responsive poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels

Poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels were prepared by thermal free‐radical copolymerization of N‐acryloyl‐N′‐ethyl piperazine (AcrNEP) and N‐isopropylacrylamide (NIPAM) in solution using N, N′‐methylene bisacrylamide as the crosslinking agent. The gels were responsive to changes in external stimuli such as pH and temperature. The pH and temperature responsive character of the gels was greatly dependent on the monomer content, namely AcrNEP and NIPAM, respectively. The gels swelled in acidic (pH 2) and de‐swelled in basic (pH 10) solutions with a response time of 60 min. With increase in temperature from 23 to 80 °C the swelling of the gels decreased continuously and this effect was different in acidic and basic solutions. The temperature dependence of equilibrium water content of the gels was evaluated by the Gibbs–Helmholtz equation. Detailed analysis of the swelling properties of these new gels in relation to molecular heterogeneity in acidic (pH 2) and basic (pH 10) solutions were performed. Water transport property of the gels was studied gravimetrically. In acidic solution, the diffusion process was non‐Fickian (anomalous) while in basic solution, the diffusion was quasi‐Fickian. The effect was more evident in solution of pH 2 than in pH 10. Various structural parameters of the gels such as number‐average molar mass between crosslink (M_c), the crosslink density (ρ_c), and the mesh size (ξ) were evaluated. The mesh sizes of the hydrogels were between 64 and 783 Å in the swollen state in acidic solution and 20 and 195 Å in the collapsed state in basic solution. The mesh size increased between three to four times during the pH‐dependent swelling process. The amount of unbound water (free water) and bound water of the gels was also evaluated using differential scanning calorimetry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Reducibly degradable hydrogels of PNIPAM and PDMAEMA: Synthesis,stimulus‐response and drug release

Reducibly degradable hydrogels of poly(N‐isopropylacrylamide) (PNIPAM) and poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) were synthesized by the combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and click chemistry. The alkyne‐pending copolymer of PNIPAM or PDMAEMA was obtained through RAFT copolymerization of propargyl acrylate with NIPAM or DMAEMA. Bis‐2‐azidyl‐isobutyrylamide of cystamine (AIBCy) was used as the crosslinking reagent to prepare reducibly degradable hydrogels by click chemistry. The hydrogels exhibited temperature or pH stimulus‐responsive behavior in water, with rapid response, high swelling ratio, and reproducible swelling/shrinkage cycles. The loading and release of ceftriaxone sodium proved the feasibility of the hydrogels as the stimulus‐responsive drug delivery system. Furthermore, the presence of disulfide linkage in AIBCy favored the degradation of hydrogels in the reductive environment. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3604–3612, 2010     

Effects of pigments on the volume‐phase‐transition properties of N‐isopropylacrylamide gels as light‐modulation materials

The effects of pigments contained in N‐isopropylacrylamide (NIPAM) gels on their volume‐change properties were investigated. All the NIPAM gel particles, containing various kinds and concentrations of pigments, showed a volume phase transition at 34 °C. No pigment affected the volume‐phase‐transition temperature of the NIPAM gels. As the concentration of the pigment in the NIPAM gels was increased, the amount of the volume change of the NIPAM gels was reduced. The water absorptivity of the NIPAM gels in the swollen state decreased as the pigment concentration increased, whereas the water absorptivity in the shrunken state was almost constant. Reducing the initial monomer concentration of the polymerization of the NIPAM gel increased the water absorptivity in the swollen state. With an increase in the water absorptivity, the volume changes of the NIPAM gels containing pigments were increased. Prototype light modulators in which the NIPAM gel particles containing pigment were dispersed between glass plates were fabricated. The light modulator using the gel particles with improved diameter change (d/d₀ = 2.3, where d and d₀ are the equilibrium diameter and the diameter of the fully shrunken state at 50 °C, respectively) exhibited a larger transmittance change from 8 to 79% than that using the gel particles before the improvement (d/d₀ = 1.7; from 38 to 79%) according to temperature changes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4644–4655, 2006     

Nearly monochromatic red electroluminescence from a nonconjugated polymer containing carbazole segments and phenanthroline [Eu(β‐diketonate)3] moieties

A novel nonconjugated copolymer (PVKEu) with carbazole segments and phenanthroline [Eu(β‐diketonate)₃] moieties was synthesized via free radical copolymerization, and characterized by FTIR, ¹H NMR spectroscopy, GPC, ICP, and elemental analysis. The copolymer exhibited good solubility, as well as good thermal stability and high glass transition temperature. The photoluminescence (PL) of this polymer in solution and in solid film has been studied. A multi‐layer device with the configuration of ITO/PEDOT: PSS (40 nm)/PVKEu (70 nm)/BCP (15 nm)/AlQ₃ (30 nm)/LiF/Al exhibited nearly monochromatic red emission at 615 nm and voltage‐independent spectral stability. Our results suggest that enhancing the ligand‐mediated energy transfer between the matrix polymer and europium complex is a potential method to improve the electroluminescence performance of the Eu‐chelated polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 210–221, 2009     

Synthesis and characterization of temperature‐ and pH‐sensitive hydrogels based on poly(2‐ethyl‐2‐oxazoline) and poly(D,L‐lactide)

A novel series of temperature‐ and pH‐sensitive hydrogels based on poly(2‐ethyl‐2‐oxazoline) and three‐arm poly(D,L ‐lactide) were synthesized via photocopolymerization. For the creation of polymeric networks, two types of macromers terminated with methacrylate groups were prepared: poly(2‐ethyl‐2‐oxazoline) dimethacrylate and three‐arm poly(D,L ‐lactide) trimethacrylate. The chemical structures were analyzed with ¹H NMR and Fourier transform infrared techniques. The thermal behaviors, morphologies, and swelling properties were measured for the characterization of the polymeric networks. All the poly(2‐ethyl‐2‐oxazoline)/three‐arm poly(D,L ‐lactide)hydrogels provided high water retention capacity and exhibited reversible swelling–shrinking behavior in response to temperature and pH variations. The hydrogels with higher poly(2‐ethyl‐2‐oxazoline) dimethacrylate contents were more effective in raising the swelling ratio and temperature and pH sensitivity. However, higher contents of three‐arm poly(D,L ‐lactide) trimethacrylate produced larger particles and pore sizes in the hydrogels. This study effectively proves that this unique combination of water swellability and biodegradability provides hydrogels with a much wider range of applications in biomedical fields. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1112–1121, 2002     

Chiral,pH responsive hydrogels constructed by N‐Acryloyl‐alanine and PEGDA/α‐CD inclusion complex: preparation and chiral release ability

Chiral, pH‐responsive hydrogels are constructed by poly(ethylene glycol) diacrylate/α‐cyclodextrin (PEGDA/α‐CD) inclusion complex and L‐N‐acryloyl‐alanine or D‐N‐acryloyl‐alanine (L‐NAA or D‐NAA) by an effective free radical polymerization approach. PEGDA containing two C=C end groups was used simultaneously to introduce α‐CD units in the resulting hydrogels and to serve as a cross‐linking agent, by which forming the designed hydrogels in quantitative yield. Hydrophilic α‐CD moieties acted as pore‐forming agent, while the L(D)‐NAA‐based polymer chains bearing –COOH groups enabled the hydrogels to display remarkable swelling–deswelling behavior in response to pH variation. The chiral NAA monomer‐derived polymer chains rendered the hydrogels with intriguing optical activity, according to circular dichroism spectra. Scanning electron microscopy revealed the uniformly porous microstructures of hydrogels. More remarkably, the L‐NAA‐based hydrogels preferentially adsorbed trans‐4‐hydroxy‐d ‐proline and preferentially released trans‐4‐hydroxy‐l ‐proline, while D‐NAA‐based hydrogels provided opposite results. The hydrogels also demonstrated remarkable enantioselective release ability towards chiral drug ibuprofen. Copyright © 2015 John Wiley & Sons, Ltd.     

A strategy for synthesis of ion‐bonded amphiphilic miktoarm star copolymers via supramolecular macro‐RAFT agent

Amphiphilic supramolecular miktoarm star copolymers linked by ionic bonds with controlled molecular weight and low polydispersity have been successfully synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization using an ion‐bonded macromolecular RAFT agent (macro‐RAFT agent). Firstly, a new tetrafunctional initiator, dimethyl 4,6‐bis(bromomethyl)‐isophthalate, was synthesized and used as an initiator for atom transfer radical polymerization (ATRP) of styrene to form polystyrene (PSt) containing two ester groups at the middle of polymer chain. Then, the ester groups were converted into tertiary amino groups and the ion‐bonded supramolecular macro‐RAFT agent was obtained through the interaction between the tertiary amino group and 2‐dodecylsulfanylthiocarbonylsulfanyl‐2‐methyl propionic acid (DMP). Finally, ion‐bonded amphiphilic miktoarm star copolymer, (PSt)₂‐poly(N‐isopropyl‐acrylamide)₂, was prepared by RAFT polymerization of N‐isopropylacrylamide (NIPAM) in the presence of the supramolecular macro‐RAFT agent. The polymerization kinetics was investigated and the molecular weight and the architecture of the resulting star polymers were characterized by means of ¹H‐NMR, FTIR, and GPC techniques. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5805–5815, 2008     

Poly(methacrylamide‐co‐2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) hydrogels: Investigation of pH‐ and temperature‐dependent swelling characteristics and their characterization

Novel poly(methacrylamide‐co‐2‐acrylamido‐2‐methyl‐ 1‐propanesulfonic acid) (poly(MAAm‐co‐AMPS)) hydrogels were synthesized by free radical polymerization of methacrylamide (MAAm) and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) in deionized water at 60 °C by using ammonium peroxydisulfate (APS), N,N′‐methylenebisacrylamide (MBAAm) and N,N,N′,N′‐tetramethylethylenediamine (TEMED) as initiator, crosslinker, and activator, respectively. To investigate the effects of feed content on the pH‐ and temperature‐dependent swelling behavior of poly(MAAm‐co‐AMPS), molar ratio of MAAm to AMPS in feed was varied from 90/10 to 10/90. Structural characterization of gels was performed by Fourier transform infrared (FTIR) spectroscopy using attenuated total reflectance (ATR) technique. Thermal and morphological characterizations of gels were performed by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. Although an apparent pH‐sensitivity was not observed for the poly(MAAm‐co‐AMPS) gels during the swelling in different buffer solutions, their temperature‐sensitivity became more evident with the increase in AMPS content of copolymer. Thermal stability of poly(MAAm‐co‐AMPS) gels increased with MAAm content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

A novel sodium carboxymethylcellulose/poly(N‐isopropylacrylamide)/Clay semi‐IPN nanocomposite hydrogel with improved response rate and mechanical properties

A novel semi‐IPN nanocomposite hydrogel (CMC/PNIPA/Clay hydrogel) based on linear sodium carboxymethylcellulose (CMC) and poly(N‐isopropylacrylamide) (PNIPA) crosslinked by inorganic clay was prepared. The structure and morphology of these hydrogels were investigated and their swelling and deswelling kinetics were studied in detail. TEM images showed that the clay was substantially exfoliated to form nano‐dimension platelets dispersed homogeneously in the hydrogels and acted as a multifunctional crosslinker. The CMC/PNIPA/Clay hydrogels swell faster than the corresponding PNIPA/Clay hydrogels at pH 7.4, whereas they swell slower than the PNIPA/Clay hydrogels at pH 1.2. The CMC/PNIPA/Clay nanocomposite hydrogels showed much higher deswelling rates, which was ascribed to more passway formed in these hydrogels for water to diffuse in and out. The deswelling process of the hydrogels could be approximately described by the first‐order kinetic equation and the deswelling rate decreased with increasing clay content. The mechanical properties of the CMC/PNIPA/Clay nanocomposite hydrogels were analyzed based on the theory of rubber elasticity. It was found that with increasing clay content, the effective crosslink chain density, v_e, increased whereas the molecular weight of the chains between crosslinks M_c decreased. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1546–1555, 2008     

Synthesis and self‐assembly of tadpole‐shaped organic/inorganic hybrid poly(N‐isopropylacrylamide) containing polyhedral oligomeric silsesquioxane via RAFT polymerization

Aminopropylisobutyl polyhedral oligomeric silsesquioxane (POSS) was used to prepare a POSS‐containing reversible addition‐fragmentation transfer (RAFT) agent. The POSS‐containing RAFT agent was used in the RAFT polymerization of N‐isopropylacrylamide (NIPAM) to produce tadpole‐shaped organic/inorganic hybrid Poly(N‐isopropylacrylamide) (PNIPAM). The results show that the POSS‐containing RAFT agent was an effective chain transfer agent in the RAFT polymerization of NIPAM, and the polymerization kinetics were found to be pseudo‐first‐order behavior. The thermal properties of the organic/inorganic hybrid PNIPAM were also characterized by differential scanning calorimetry. The glass transition temperature (T_g) of the tadpole‐shaped inorganic/organic hybrid PNIPAM was enhanced by POSS molecule. The self‐assembly behavior of the tadpole‐shaped inorganic/organic hybrid PNIPAM was investigated by atomic force microscopy and dynamic light scattering. The results show the core‐shell nanostructured micelles with a uniform diameter. The diameter of the micelle increases with the molecular weight of the hybrid PNIPAM. Surprisingly, the micelle of the tadpole‐shaped inorganic/organic hybrid PNIPAM with low molecular weight has a much bigger and more compact core than that with high molecular weight. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7049–7061, 2008