A Temperature-sensitive Hydrogel Refolding System: Preparation of Poly(N-isopropyl acrylamide) and Its Application in Lysozyme Refolding

Temperature-sensitive hydrogel—poly(N-isopropyl acrylamide) (PNIPA) was prepared and applied to protein refolding. PNIPA gel disks and gel particles were synthesized by the solution polymerization and inverse suspension polymerization respectively. The swelling kinetics of the gels was also studied. With these prepared PNIPA gels, the model protein lysozyme was renatured. Within 24h, PNIPA gel disks improved the yield of lysozyme activity by 49.3% from 3375.2U·mg^-1 to 5038.8U·mg^-1. With the addition of faster response PNIPA gel beads, the total lysozyme activity recovery was about 68.98% in 3h, as compared with 42.03% by simple batch dilution. The novel refolding system with PNIPA enables efficient refolding especially at high protein concentrations. Discussion about the mechanism revealed that when PNIPA gels were added into the refolding buffer, the hydrophobic interactions between denatured proteins and polymer gels could prevent the aggregation of refolding intermediates, thus enhanced the protein renaturation.

Phototactic Poly(N-isopropyl acrylamide)Microgels with Photoresponsive Property

Smart functional microgels hold great potential in a variety of applications,especially in drug transportation.However,current drug carriers based on physiological internal stimuli cannot efficiently orientate to designated locations.Therefore,it is necessary to introduce the self-propelled particles to the drug release of the microgels.In order to study self-propulsion of microgels induced by light,it is also a challenge to prepare micronsized microgels so that they can be observed directly under optical microscopes.In this work,phototactic microgels with photoresponsive properties are prepared.The microgel particles can be observed by confocal laser scanning microscopy.The photoresponsive properties of microgels are fully investigated by various instruments.Light can also regulate the state of the microgel solution,making it switch between turbidity and clarity.The phototaxis of particles irradiated by UV light was studied,which may be used for microgels enrichment and drug transportation and release.

POLY(N-ISOPROPYL ACRYLAMIDE) MICROGEL DOPED WITH LUMINESCENT PBS QUANTUM DOTS

Thiol-stabilized PbS quantum dots （QDs） with dimensions 3-5 nm capped with a mixture of 1-thioglycerol/dithioglycerol （TGL/DTG） were coUoidally prepared at room temperature. Room temperature photoluminescence quantum efficiency of freshly prepared PbS QDs （7%-11%） remained higher than 5% upon aging for three weeks when the nanocrystals （NCs） were stored in an ice-bath in the dark, and higher than 5%for at least five weeks when extra DTG ligands were introduced into the nanocrystal solution followed by stirring every two weeks. Poly（N-isopropyl acrylamide） （PNIPAM） microgels were produced via precipitation polymerization with dimensions of ca. 230 nm and polydispersity of 3-5%. Incorporation of PbS QDs into PNIPAM microgels indicated that PbS can be incorporated into the interior of microgel particles and not at the microgel interface. The combination of reasonable room temperature quantum efficiency and strong, efficient luminescence covering the 1.3-1.55 μm telecommunication window makes these nanoparticles promising materials in optical devices and telecommunications.

Synthesis and Properties of Poly (N-isopropylacrylamide) and Poly (N-isopropylacrylamide-co-acrylamide) Hydrogels

The thermosensitive poly （ N-isopropylacrylamide ） （PNIPAAm） and poly （N-isopropylacrylamide-co-acrylamide） [ poly （NIPAAm-co-AAm） ] hydrogels with different acrylamide molar percentage are prepared by radiation polymerization using Co^60 γ-ray. Their swelling equilibrium data in the media of deionized water, NaCl aqueous solutions and different pH buffer solutions are determined. It appears that lower critical solution temperature （LCST） of the hydrogels will drop with the increase of ionic strength and increase with the rising of acrylamide content, A semi-empirical formula is set up with the experimental results. Moreover, it also indicates that this copolymer is pH-sensitive, which is similar to the homopolymer of PNIPAAm.

¹³C NMR and Raman Studies of Fullerene-Based Poly (Acrylamides)

A new classification of the different types of fullerene-containing polymers is presented according to their different properties and applications they exhibit in a variety of fields. 13C NMR and Raman studies of a series of polymeric samples of fullerene-grafted poly (acrylamide), which were prepared by systematic variation of concentration of fullerene and acrylamide, are described. 13C NMR spectral analysis of the polymeric samples showed a peak for fullerene at 143 δppm and for poly (acrylamide) between 170 and 180 δppm and Raman spectral analysis of the poly-meric samples gave the Raman band for fullerene between 1470 cm-1 and poly (acrylamide) at 2800 cm-1. The Tg value, obtained from DSC results, showed a high glass transition temperature at 100.94°C revealing the presence of fullerene in the polymeric matrix. TGA analysis shows that polymer is thermally stable up to 340°C.

Poly (Acrylamide-co-Acrylic Acid) Hydrogel Induced by Glow-Discharge Electrolysis Plasma and Its Adsorption Properties for Cationic Dyes

In this paper, poly （acrylamide-co-acrylic acid） （P（AM-co-AA）） hydrogel was pre- pared in an aqueous solution by using glow-discharge electrolysis plasma （GDEP） induced copoly- merization of acrylamide （AM） and acrylic acid （AA）, in which N,N＇-methylenebisacrylamide （MBA） was used as a crosslinker. A mechanism for the synthesis of P（AM-co-AA） hydrogel was proposed. To optimize the synthesis condition, the following parameters were examined in detail： the discharge voltage, discharge time, the content of the crosslinker, and the mass ratio of AM to AA. The results showed that the optimum pH range for cationic dyes removal was found to be 5.0-10.0. The P（AM-co-AA） hydrogel exhibits a very high adsorption potential and the ex- perimental adsorption capacities for Crystal violet （CV） and Methylene blue （MB） were 2974.3 mg/g and 2303.6 mg/g, respectively. The adsorption process follows a pseudo-second-order kinetic model. In addition, the adsorption mechanism of P（AM-co-AA） hydrogel for cationic dyes was also discussed.

SYNTHESIS OF POLYMERIC β-CYCLODEXTRIN SUPPORTED BY CROSSLINKED POLY(ACRYLAMIDE-co-VINYLAMINE)AND ITS CATALYSIS OF THE HYDROLYSIS OF p-NITROPHENYL ACETATE

Polymeric β-cyclodextrin (β-CD) supported by crosslinked poly(acrylamide-co-vinylamine) was synthesized as anartificial analog of hydrolytic enzyme and its catalysis of the hydrolysis of p-nitrophenyl acetate (p-NPA) was theninvestigated. The result showed that the polymer-supported β-CD could accelerate the hydrolytic reaction of p-NPA morequickly than β-CD itself and crosslinked poly(acrylamide-co-vinylamine) alone. The acceleration rate of the polymer-supported β-CD was about 10 times as fast as that of free β-CD in 0.01 mol/L phosphate buffer (pH 7.4) containing 32%DMSO at 37±0.1℃ when the molar amount of β-CD units in the polymer was equal to that of free β-CD in the experiments.The enhanced acceleration of thc polymer-supported β-CD should be ascribed to the cooperative contribution of theinclusion effect of β-CD ring and the nucleophilic effect of amino groups on the polymeric support.

A Novel Sieving Medium for Separation of DNA Fragments-Poly(acrylamide-dimethylacrylamide)

A short chain poly (acrylamide-dimethylacrylamide) was synthesized in water phase using isopropanol as a chain transfer agent. This copolymer can form a stable dynamic coating on the inner surface of the capillary, thereby suppressing the electroosmotic flow and DNA-capillary wall interaction. The high efficient separation of DNA fragments and SSCP analysis were obtained in bare capillaries using this copolymer as a sieving medium.

IMMOBILIZATION OF Saccharomyces Cerevisiae USING POLY(ACRYLAMIDE)GEL FOR ASYMMETRIC SYNTHESIS OF R(-)-MANDELIC ACID

In this paper,the poly(acrylamide)hydrogel used to immobilize saccharomyces cerevisiae for asymmetric synthesis of R(-)-mandelic acid was prepared with free radical ploymerization in deionized water at room temperature under nitrogen atmosphere.The influence of the composition of hydrogel,loading amount of cells and culture conditions on the asymmetric synthesis was investigated.Results show that PAAm hydrogel is a feasible carrier for immobilization of cells which is a potential alternative method to prepare enantiomerically pure R(-)-mandelic acid.

Synthesis and Characterization of Poly(styrene-co-acrylamide) Polymers Prior to Electrospinning

Electrospun nanofibers present a new and rapidly growing research area due to their pronounced micro and nano characteristics associated with high surface area to volume ratio. Poly(styrene-co-acrylamide) and polystyrene polymers were synthesized by boiling temperature soap free emulsion polymerization in aqueous medium with potassium peroxosulphate as the initiator. The resulting polymers were dissolved in dimethylformamide and teterahydrofuran (DMF: THF) (4:1) to form polymer solutions that were electrospun into fiber mats with diameters ranging from 1.84 - 2.53 μm and 5.01 μm, respectively. The fibers were characterized by Fourier transform infrared spectroscopy (FTIR) equipped with universal ATR sampling accessory (4000 - 400 cm-1). The morphology and size were examined by a scanning electron miscroscope (SEM) and the thermal properties by thermogravimetric analysis (TGA). The FTIR spectra of the poly(styrene-co-acrylamide) revealed the presence of acrylamide on the polystyrene chain. Thus, surface modification of polystyrene with acrylamide is possible in a single step polymerization reaction prior to electrospinning.

Blood Compatibility of Amphiphilic Poly(N-α-acrylamide-L-lysine-<i>b</i>-dimethylsiloxane) Block Copolymers

Amphiphilic block copolymers poly(LysAA-b-DMS) consisting of a hydrophilic poly(N-α-acrylamide-L-lysine) [poly(LysAA)] segment with different molecular weights and a hydrophobic polydimethylsiloxane (PDMS) segment were prepared as follows. The precursor copolymer poly(Boc-LysAA-OtBu-b-PDMS) was obtained from radical polymerization of N-α-acrylamide-N-ε-tert-butoxycarbonyl-L-lysine-tert-butylester (Boc-LysAA-OtBu) initiated with 4,4’-azobis(polydimethylsiloxane 4-cyanopentanoate) (azo-PDMS) with the molecular weight of PDMS Mw = 4.3 × 103 in the presence of 2-mercaptoethanol (2-ME) as a chain-transfer agent. Removal of the protecting groups of the precursor copolymer was carried out in 80% trifluoroacetic acid aqueous solution to give poly(LysAA-b-DMS)-1-3. The weight average molecular weight of poly(LysAA-b-DMS)-1-3 was Mw = 1.02 × 104 – 2.52 × 104. From the 1H-NMR and fluorescence spectra measurements, poly(LysAA-b-DMS)-1-3 was determined to self-organize and form core-shell micelles in water. The critical micelle concentration (CMC) increased to 1000 - 4000 mg·L–1 with increasing molar ratio of the poly(LysAA) segment from 0.42 to 0.65. From morphological analysis with a scanning probe microscope (SPM), poly(LysAA-b-DMS) has microphase-separated structures made up of hydrophilic and hydrophobic regions with the domain size ranging from several tens to several hundreds of nanometers. Inhibition of thrombin activity of poly(LysAA-b-DMS) was evaluated from the Michaelis constant (KM) and catalytic activity (kcat) for the enzymatic reaction of thrombin and synthetic substrate S-2238 in the presence of poly(LysAA-b-DMS). The KM and kcat were 0.10 - 0.11 mM and 4.04 × 105 – 4.26 × 105 min–1, respectively. Fibrinolytic activity was also verified from the transformation of plasminogen to plasmin by tissue plasminogen activator (t-PA) using synthetic substrate S-2251 in the presence of poly(LysAA-b-DMS). The KM and kcat were 0.07 mM and 5.73 × 106 –5.95 × 106 min–1, respectively.

Poly(Acrylamide-Co-Acrylic Acid)-Zinc Acetate Polymer Electrolytes: Studies Based on Structural and Morphology and Electrical Spectroscopy

Solid polymer electrolytes (SPEs) of polyacrylamide-co-acrylic acid (PAA) as the polymer host and zinc acetate (ZnA) as an ionic dopant were prepared using a single solvent by the solution casting technique. The amorphous and crystalline structures of film were investigated by X-ray diffraction (XRD). The surface morphology of samples was examined by scanning electron microscopy (SEM). The composition and complex formation of films were characterized by Fourier transform infrared (FTIR) spectroscopy. The conductivity of the PAA-ZnA films was determined by electrochemical impedance spectroscopy. According to the XRD and FTIR analyses, all electrolyte films were in amorphous state and the existence of interaction between Zn2+ cations and the PAA structure confirms that the film was successfully prepared. The SEM observations reveal that the electrolyte films appeared to be rough and flat with irregularly shaped surfaces. The highest ionic conductivity (σ) of 1.82 × 10-5 Scm-1 was achieved at room temperature (303 K) for the sample containing 10 wt % ZnA.

Influence of acrylamide monomer addition to the acrylic denture-base resins on mechanical and physical properties

The aim of the study was to evaluate the effect of adding acrylamide monomer （AAm） on the characterization, flexural strength, flexural modulus and thermal degradation temperature of poly（methyl methacrylate） （PMMA） denture-base resins. Specimens （n= 10） were fabricated from a conventional heat-activated QC-20 （Qc-） and a microwave heat-activated Acron MC （Ac-） PMMA resins. Powder/ liquid ratio followed the manufacturer＇s instructions for the control groups （Qc-c and Ac-c） and for the copolymer groups, the resins were prepared with 5% （-5）, 10% （- 10）, 15% （- 15） and 20% （-20） acrylamide contents, according to the molecular weight ratio, respectively. The flexural strength and flexural modulus were measured by a three-point bending test. The data obtained were statistically analyzed by Kruskal-Wallis test （a=O.05） to determine significant differences between the groups, The chemical structures of the resins were characterized by the nuclear magnetic resonance spectroscopy. Thermal stabilities were determined by thermogravimetric analysis （TGA） with a heating rate of 10 ~C.min-1 from 35 ~C to 600 ~C. Control groups from both acrylic resins showed the lowest flexural strength values. Qc-15 showed significant increase in the flexural strength when compared to Qc-c （P〈O.01）. Ac-10 and Ac-15 showed significance when compared to Ac-c （P〈O.01）. Acrylamide incorporation increased the elastic modulus in Qc-10, Qc-15 and Qc-20 when compared to Qc-c （P〈0.01）. Also significant increase was observed in Ac-10, Ac-15 and Ac-20 copolymer groups when compared to Ac-c （P〈0.01）. According to the 1H-nuclear magnetic resonance （NMR） results, acrylamide copolymerization was confirmed in the experimental groups. TGA results showed that the thermal stability of PMMA is increased by the insertion of AAm.

Molecular chain properties of poly(N-isopropyl acrylamide)

A series of poly(N-isopropyl acrylamide) (PNIPAM) samples with molecular weight ranging from 2.23 × 104 to 130 × 104 and molecular weight distributionMw/Mn ≤1. 28 were obtained by free radical polymerization and repeat precipitation fractionation. The molecular weightMw, second virial coefficientA2 as well as the mean-square-root radius of gyration < S2 > for PNIPAM samples in tetrahydrofuran (THF) were determined by light scattering, and the relations were estimated atA2 ∞ M w- 0.25 and S2 1/2 = 1.56 × 10-9 Mw 0.56. The intrinsic viscosity for THF solution and methanol solution of PNIPAM samples was measured and the Mark-Houwink equations were obtained as [η] =6.90x 10-5 M0. 73(THF solution) and [η] = 1.07 × 10-4 M0.71(methanol solution). The above results indicate that both THF and methanol are good solvents for PNIPAM. The limit characteristic ratioC ∞ for PNIPAM in the two solutions was determined to be 10.6 by using Kurata-Stockmayer equation, indicating that the flexibility of PNIPAM chain is close to that of polystyrene. The intrinsic viscosity for the aqueous solution of PNIPAM was measured at 25-30.5°C. The result demonstrates that PNIPAM chain begins to shrink at 25°C, and from about 30°C, onward the molecular chain shrinks much more sharply till the solution becomes macroscopically unstable at 32°C.

Thermal reversible gelation during phase separation of poly(N-isopropyl acrylamide)/water solution

By dynamic viscoelastic measurement for PNIPAM/water solution it has been found that below the phase separation temperature (about 32°C), the system is homogeneous fluid; while upon being heated to about 32°C, the solution undergoes phase separation and the storage modulus G’ increases sharply and exceeds the loss modulus G”, indicating the physical network formation during the phase separation. Based on the percolation model, the gel points Tgel were obtained by applying the dynamic scaling theory (DST) and Winter’s criterion. The critical exponent n was also obtained to be 0.79 through DST, which is different from 0.67, the critical point of chemically crosslinked network predicted through DST. The obtained n value reflects the special property of physical network being different from chemical network.

Poly(N-isopropylacrylamide)-grafted Dual Stimuli-responsive Filter Paper for Protein Separation

Thermal and salt dual stimuli-responsive filter-paper-based membranes were prepared by UV-induced grafting of NIPAM-based polymers on paper surface. The grafting ratio could be controlled by monomer concentration during grafting polymerization. The results from pressure drop measurement of the mobile phase flowed cross the membrane demonstrate that an appropriate grafting ratio would be 8%-10%. Protein adsorption on the membrane through hydrophobic interaction could be promoted by increasing temperature and lyotropic salt concentration. The effect of grafted polymer structure on protein binding performance was studied. Filter paper grafted with NIPAM-based branched copolymer consisting of hydrophobic monomer moieties shows ten times higher protein binding capacity than that of the original filter paper. The separation of plasma proteins using the dual stimuli-responsive membrane was examined to demonstrate feasible application for hydrophobic interaction chromatographic separation of proteins.

基于线形聚丙烯酰胺聚合物溶液流变学行为的影响因素

通过溶液聚合合成了线形聚丙烯酰胺(LPA),分别在LPA水溶液中聚合N,N-二甲基丙烯酰胺(DMA)和N-羟乙基丙烯酰胺(HEA),合成了LPA/PDMA和LPA/PHEA准互穿聚合物网络。研究了LPA黏均分子量、剪切速率、温度等因素对上述准互穿聚合物网络流变学的影响。结果表明,LPA溶液的临界缠结浓度随着黏均分子量的增加而下降;LPA、LPA/PHEA和LPA/PDMA溶液均表现出明显的剪切变稀行为,LPA/PHEA和LPA/PDMA溶液黏度要显著小于对应黏均分子量的LPA溶液的黏度;聚合物溶液黏度均随温度的升高而下降,并且LPA/PHEA、LPA/PDMA溶液对温度更加敏感。黏弹性结果显示:当聚合物的质量浓度为0.025 g/mL时,基于中、高黏均分子量LPA的聚合物溶液以弹性为主,聚合物网络结构较稳定;基于低黏均分子量LPA的聚合物溶液则以黏性为主,聚合物网络结构不稳定,易被外力破坏。

全物理交联导电双网络水凝胶κ-CG-Ca^(2+)/pHEAA的制备及性能研究

以钙离子敏感型多糖κ-卡拉胶(κ-CG)为第一网络、含羟基聚合物聚N-羟乙基丙烯酰胺(pHEAA)为第二网络,采用“加热-冷却-光聚合”方法制备了全物理交联导电双网络水凝胶κ-CG-Ca^(2+)/pHEAA;通过扫描电子显微镜、紫外可见分光光度计对水凝胶进行了表征,并测试了水凝胶的拉伸性能、自恢复性、导电性和传感性。结果表明:该水凝胶具有较强的拉伸性能(拉伸强度为1042.34 kPa,拉伸应变为17.75 mm/mm)和良好的自恢复性(恢复率为42.54%);由于自由离子的引入,该水凝胶表现出优异的导电性和传感性。这种性能优异的导电双网络水凝胶在人体运动监测、柔性电极和可穿戴电子设备等领域具有广阔的应用前景。

Phase Transition Temperature Controllable Poly(acrylamide-co-acrylic acid) Nanocomposite Physical Hydrogels with High Strength

Poly（acrylamide-co-acrylic acid） nanocomposite physical （P（AAm-co-AAc）NCP） hydrogels have been prepared through the in situ free radical solution polymerization based on a ＂single network, dual cross-linkings＂ strategy. The P（AAm-co-AAc） NCP hydrogels are composed of nanobrushes of P（AAm-co-AAc） chains grafted on the surface of vinyl- hybrid silica nanoparticles （VSNPs）. In the hydrogel system, the VSNPs act as the ＂analogous chemical cross-linking points＂ once the hydrogen bonds formed between the P（AAm-co-AAc） chains of the nanobrushes, thus leading to the fabrication of high-strength P（AAm-co-AAc） NCP hydrogels. Compared with conventional thermosensitive P（AAm-co-AAc） hydrogels, the P（AAm-co-AAc） NCP hydrogels have a broader range of phase transition temperature, which can be adjusted by altering the monomer ratio, the VSNPs concentration, the addition of urea and N,N-dimethylacrylamide （DMAAm）. At the same time, the mechanical properties of the P（AAm-co-AAc） NCP hydrogels have been improved significantly by the introduction of VSNPs. Furthermore, both the phase transition and the tensile strength of the P（AAm-co-AAc） NCP hydrogels are largely influenced when Fe3＋ ions are introduced as the ionic crosslinkers into the hydrogel networks.

聚丙烯酰胺-聚乙二醇-水体系相图及丙烯酰胺单体在两相中的分配

聚丙烯酰胺(PAAm)和聚乙二醇(PEG)两种水溶液混合时能形成双水相体系,其中上层为PEG富集相,下层为PAAm和PEG的混合相.用凝胶渗透色谱(GPC)法和浊度滴定法研究了PAAm-PEG-H2O双水相体系的相图,结果表明,随着PEG分子量的升高,体系的分相浓度下降.在PAAm-PEG20000-H2O体系中,随着体系温度升高,分相浓度先下降后升高,55℃时分相浓度最低.丙烯酰胺(AAm)单体能在两相中发生相分配,分配系数随着PAAm浓度和平衡温度的增加而增大,随着PEG浓度的增加而下降.