Preparation of Hollow Silica Microspheres via Poly（N-isopropylacrylamide）

Core-shell structured SiO2/poly（N-isopropylacrylamide） （SiO2/PNIPAM） microspheres were successfully fabricated through hydrolysis and condensation reaction of tertraethyl orthosilicate （TEOS） on the surface of PNIPAM template at 50 ~C. The PNIPAM template can be easily removed by water at room temperature so that SiO2 hollow microspheres were finally obtained. The transmission electron microscope and scanning electron microscope observations indicated that SiO2 hollow microspheres with an average diameter of 150 nm can be formed only if there are enough concentration of PNIPAM and TEOS, and the hy- drolysis time of TEOS. FTIR analysis showed that part of PNIPAM remained on the wall of SiO2 because of the strong interaction between PNIPAM and silica. This work provides a clean and efficient way to prepare hollow microspheres.

Rheological behavior of ZnO suspension with thermosensitive poly(N-isopropylacrylamide) for colloidal processing of ceramics

Novel colloidal processing using thermosensitive poly（N-isopropylacrylamide） （PNIPAM） as a coagulating agent has beendeveloped to prepare complex-shaped ceramic components. In this work, the properties of PNIPAM aqueous solutions and therheological behavior of ZnO suspensions with PNIPAM were investigated. The results show that the PNIPAM solutions exhibitobvious thermosensitivity and its transition temperature is around 32℃. When the temperature is above 40℃ （Tc, the criticaltransition temperature of thermosensitive suspension）, the 50% ZnO （volume fraction） suspension with 8 mg/mL PNIPAM has asharp increase in viscosity and reaches up to 11.49 Pa·s at 50℃, displaying strong elasticity. The main reasons are the increase ofeffective volume fraction attributed to precipitation of PNIPAM segments and the flocculation between ZnO powder particles. Inaddition, the maximum solid loading （volume fraction） at 20 ℃ is higher than that at 40℃, which proves that the phase transition ofPNIPAM can induce the flocculation of suspension.

Effect of Graft Yield on the Thermo-Responsive Permeability Through Porous Membranes with Plasma-Grafted Poly(N-isopropylacrylamide)Gates

The effect of graft yield on both the thermo-responsive hydraulicpermeability and the therrno-responsive diffusional permeability through porous membranes withplasma-grafted poly(N-isopropylacrylamide) (PNIPAM) gates was investigated. Both thermo-responsiveflat membranes and core-shell microcapsule membranes with a wide range of graft yield of PNIPAM wereprepared using a plasma-graft pore-filling polymerization method. The grafted PNIPAM was formedhomogeneously throughout the entire thickness of both the flat polyethylene membranes and themicrocapsule polyamide membranes. Both the hydraulic permeability and the diffusional permeabilitywere heavily dependent on the PNIPAM graft yield. With increasing the graft yield, the hydraulicpermeability (water flux) decreases rapidly at 25℃ because of the decrease of the pore size;however, the water flux at 40℃ increases firstly to a peak because of the increase ofhydrophobicity of the pore surface, and then decreases and finally tends to zero because of the poresize becoming smaller and smaller. For the diffusional permeability, the temperature showsdifferent effects on the diffusional permeability coefficients of solutes across the membranes. Whenthe graft yield was low, the diffusional coefficient of solute across the membrane was higher attemperature above the lower critical solution temperature (LCST) than that below the LCST; however,when the graft yield was high, the diffusional coefficient was lower at temperature above the LCSTthan that below the LCST. It is very important to choose or design a proper graft yield of PNIPAMfor obtaining a desired thermo-responsive 'on/off' hydraulic or diffusional permeability.

Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide) synthesized by ATRP

Novel Y-shaped block copolymers of poly（ethylene glycol） and poly（N-isopropylacrylamide）, PEG-b-（PNIPAM）2, were successfully synthesized through atom transfer radical polymerization （ATRP）. A difunctional macroinitiator was prepared by esterification of 2,2-dichloroacetyl chloride with poly（ethylene glycol） monomethyl ether （PEG）. The copolymers were obtained via the ATRP ofN-isopropylacrylamide （NIPAM） at 30℃ with CuCl/Me6TREN as a catalyst system and DMF/H2O （v/v = 3：1） mixture as solvent. The resulting copolymers were characterized by gel permeation chromatography （GPC） and ^1H NMR. These block copolymers show controllable molecular weights and narrow molecular weight distributions （PDI 〈 1.15）. Their phase transition temperatures and the corresponding enthalpy changes in aqueous solution were measured by differential scanning calorimetry （DSC）. As a result, the phase transition temperature of PEG45-b-（PNIPAM55）2 is higher than that of PNIPAM, however, the corresponding enthalpy change is much lower, indicating the significant influence of the macromolecular composition and architecture on the phase transition.

In-Situ Synthesized Myoglobin Imprinted Poly(N-Isopropylacrylamide)/Silica Nanocomposite Gels by Using the Molecular Imprinting Method

Temperature sensitive imprinted poly(N-isopropylacrylamide) nanocomposite gels were syntheses via in-situ, free radical crosslinking polymerization of corresponding monomer in nano-sized silica and five different concentrations of myoglobin solution by using the molecular imprinting method. Mb adsorption from five different concentrations of Mb solutions was investigated by two types of nanocomposite gel systems prepared by non-imprinted and imprinted methods. Nanocomposite gels imprinted with Mb showed higher adsorption capacity and specificity for Mb than nanocomposite gels prepared by the usual procedure. The highest Mb adsorption was observed via the imprinted nanocomposite gels with 12.5% Mb. In addition, selectivity studies were also performed by using two reference molecules as fibrinogen and hemoglobin. The imprinted nanocomposite gels had higher adsorption capacity for Mb than the non-imprinted gels and also exhibited good selectivity for Mb and high adsorption rate depending on the number of Mb sized cavities.

Microwave-assisted Preparation of Temperature Sensitive Poly(N-isopropylacrylamide) Hydrogel with Improved Responsive Properties

Poly（N-isopropylacrylamide）-based hydrogel was prepared under microwave irradiation The hydrogel thus prepared, comparing with that prepared by thermal heating method, exhibits faster swelling and shrinking kinetics. The improved responsive properties are due to the more heterogeneous and porous networks formed under microwave irradiation.

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.

THE ADSORPTION OF LINEAR POLY(N-ISOPROPYLACRYLAMIDE)CHAINS ON SURFACTANT-FREE POLYSTYRENE NANOPARTICLES

The adsorption of linear poly(N-isopropylacrylamide) (PNIPAM) chains on surfactant-free polystyrene (PS) nanoparticles was used as a model system to study the hydrophobic adsorption of polymer on the surface, because the hydrophobility of PNIPAM can be continuously varied by a small temperature change. The adsorption was investigated by a combination of static and dynamic laser light scattering (LLS) measurements. In static LLS, the absolute excess scattered light intensity led to the amount of PNIPAM adsorbed on the surface. In dynamic LLS, the hydrodynamic thickness of the adsorbed PNIPAM layer was accurately measured. For a given particle concentration, the adsorption increases as the PNIPAM concentration and the incubation temperature increase. The average density of the adsorbed PNIPAM layer is reciprocally proportional to the number of the PNIPAM chains on the surface, revealing a simple scaling of the chain density distribution. The adsorption follows the Langmuir's isotherm. The enthalpy change estimated from the adsorption at 25 degrees C and 30 degrees C is slightly positive, indicating that the adsorption involves the coil-to-globule transition of the chains on the surface.

New Insights into Folding Kinetics of α,ω Dye-Functionalized Poly(N-isopropylacrylamide)

Two narrowly-distributed poly(N-isopropylacrylamide)(PNIPAM) samples were prepared via atom transfer radical polymerization (ATRP) with a novel dansyl functionalized initiator. The other end of the PNIPAM was functionalized by dabcyl group via click reaction. From the static fluorescence measurements, the fluorescence intensity of dansyl group and energy transfer efficiency between dansyl and dabcyl groups increased when the temperature increased from 36 °C to 45 °C, indicating that the microenvironment surrounding dansyl became hydrophobic and the distance between dansyl and dabcyl decreased. The kinetics of the conformational change of the dye-labeled PNIPAM was studied by a home-made laser-induced temperature jump device with fluorescent measurement. Our results revealed that the characteristic transition time was 3.8 and 5.8 ms for PNIPAM with degrees of polymerization of 85 and 142, respectively, indicating that the characteristic transition time was related to the chain length. Besides, characteristic transition time for the change of the energy transfer efficiency was 2.9 ms for PNIPAM with the degree of polymerization of 85, suggesting that the energy transfer efficiency change was faster than the fluorescence intensity change of dansyl group.

Temperature-pH Sensitive IPN Hydrogels Composed of Silk Sericin and Poly(N-isopropylacrylamide)

Interpenetrating polymer network （IPN） composed of silk sericin （SS） and poly（N-isopropylacrylamide） （PNIPAAm） was prepared. The morphology of the IPNs, in which the SS phase was stained with ammonium cuprate, was examined with TEM and a relative homogeneous distribution of the two polymers was exhibited. The swelling behavior of the IPN hydrogels showed both temperature and pH dependences.

Poly(N-isopropylacrylamide)-based Vertically Sandwich-typed Hydrogel with Fast Temperature-response Speed and Its Controlled-release Characteristics

A novel poly（N-isopropylacrylamide）-based sandwich-typed hydrogel, which was featured with both ends of linear poly（N-isopropylaerylamide） （PNIPAM） chains being grafted onto cross-linked PNIPAM chains, was successfully prepared in a three-step process by a method of sequential synthesis. The proposed hydrogel displays faster and hydration/dehydration dynamic response to temperature cycling owing to linear PNIPAM chains to form big-pore structure. This work may lead to high attraction for targeting drug delivery systems, polymeric pump, sensors and so on.

Laterally Sandwich-typed Hydrogel Columns with Liner Poly(N-isopropylacrylamide) Layer:Preparation, Swelling/deswelling Kinetics and Drug Delivery Characteristics

A novel thermo-responsive hydrogel column, featured with both ends of linear poly（N- isopropylacrylarnide） （PNIPAM） chains being grafted onto cross-linked PNIPAM chains, was reported. The laterally sandwich-typed hydrogel columns were fabricated by radical polymerization in a three-step process using a method of ice-melting synthesis. The initiating path, morphology and thermoresponsive characteristics of the prepared hydrogel columns were experimentally studied. The results show that the hydrogel column obtained by the initiator inside part has more quick swelling and deswelling rates responsing to temperature cycling than other hydrogels owing to linear PNIPAM chains to form supermacroporous structure. The proposed hydrogel structure provide a new mode of the phase transition behavior for thermo-sensitive ＂smart＂ or ＂intelligent＂ monodisperse micro-actuators, which is highly attractive for targeting drug delivery systems, chemical separations, and sensors and so on.

Thermo-Responsive Electrospun Nanofibers from Poly( N-isopropylacrylamide )/Polyvinyl Pyrrolidone Blends

A novel nanofiber composite poly(N-isopropylacrylamide)(PNIPAAm)/polyvinyl pyrrolidone(PVP)was successfully prepared by electrospinning.Analogous medicated fibers loaded with ketoprofen(KET)as a model drug were prepared.X-ray diffraction(XRD)demonstrated that the drug was presented in the fibers with an amorphous form.Both scanning and transmission electron microscopy showed that the fibers had an even diameter and smooth surface,and no phase separation was observed.The KET loaded nanofibers did not affect the morphology of the fibers,and no drug aggregation was separated from the polymer fibers.Water contact angle measurements proved that the PNIPAAm/PVP fibers switched from hydrophilic to hydrophobic when the temperature increased the lower critical solution temperature of 32℃.In vitro drug release studies were also undertaken and the result indicated that the PNIPAAm/PVP blend nanofiber presented the properties of the two polymers,having temperature-sensitive systems with sustained release properties.In addition,MTT assay demonstrated that the nanofiber film was non-toxic and suitable for cell growth.Thus,the nanofiber can be used as thermoresponsive carriers for sustained release of poor water soluble drugs.

The Swelling Equilibria of N-isopropylacrylamide Based Hydrogel in Aqueous Solution of Ethanol

N-isopropylacrylamide (NIPAAm) was used to synthesize NIPAAm homopolymer (nonionized) and NIPAAm-sodium methacrylate copolymer (ionized). The swelling equilibria for both gels were obtained in aqueous solution of ethanol with concentration ranging from 0 to 100%(by mass) at 25℃. The swollen gel in water shrank first with the addition of a small amount of ethanol and then reswelled with further addition of ethanol showing not only a discontinuous volume phase transition but also a typical reentrant phenomenon. A thermodynamic model based on the UNIQUAC with the 'free-volume' contribution was applied to correlate and predict the swelling behavior of the poly(NIPAAM)-gels in ethanol-water mixture.

Transitional Process of Ploy（N-isopropylacrylamide） in Deuterated Solution

The fast phase-transitional process of ploy（N-isopropylacrylamide） （PNIPAM） in deuterated solution was studied by laser induced temperature jump technique combined with time-resolved mid-infrared absorbance difference spectroscopy on nanosecond level. The multi-peaks of amide I＇band of PNIPAM among the energy range of 1565-1700 cm^-1 was experimentally resolved to three groups （i, ii, iii） for the first time, while the distinct threestage procedure in the phase transitional process of long-chain PNIPAM was observed firstly too. Furthermore, proper assignments were also made for the three group peaks in amide I＇band and the three steps in the kinetics process of long-chain PNIPAM.

水溶液自由基聚合制备的PNIPA分子特性

采用水溶液自由基聚合方法,制备聚N-异丙基丙烯酰胺(PNIPA),探讨了PNIPA的分子特性与单体浓度、聚合温度(从0℃至50℃)的关系.研究发现,当聚合温度低于最低临界溶解温度(LCST)时,如果单体浓度达到一个临界值(n*),即使不添加任何交联剂,PNIPA分子链之间也会发生向聚合物的链转移反应,从而形成自交联凝胶,并且在提高单体浓度和降低聚合温度时自交联凝胶的含量也随之增加.此外,采用凝胶渗透色谱(GPC)测定未交联PNIPA的相对分子质量及相对分子质量分布,并探讨了它们与单体浓度的关系.

Conformational Transition of Poly （Acrylic Acid） Detected by Microcantilever Sensing

Poly （acrylic acid） （PAA） chains are grafted on one side of a microcantilever by the self-assembled method and the deflections of the microcantilever are detected as a function of medium pH from 3 to 11. It is found that when the pH varies, the microcantilever deflects because of the changing surface stress. By analysing the electrostatic repulsive effect, the surface stress change is related to the conformation transition of PAA from a collapse state to a swelling state. This method offers the interaction information among the polymer chains during the conformational transition and affords an alternative way to study conformational change of polymers.

Study on Thermosensitive Micellization of Dextran-g-PNIPAAm in Aqueous Solutions

The thermosensitive micellization of dextran-g-PNIPAAm in aqueous solutions has been investigated by fluorescence spectroscopy, dynamic light scattering and transmission electron microscope. The formed polymeric micelles showed different diameters of about 20 nm or 100 nm, when the solution temperature was below or above the phase transition temperature.

THERMAL-SENSITIVE BETA-CYCLODEXTRIN-CONTAINING POLY(NISOPROPYLACRYLAMIDE)HYDROGELS CROSSLINKED BY Si—O—Si BONDS—SYNTHESIS,CHARACTERIZATION AND PROLONGING IN VITRO RELEASE OF 5-FLUOROURACIL

A series of novel p（N-isopropylacrylamide） （PNIPAM） hydrogels were synthesized by radical copolymerization of N-isopropylacrylamide （NIPAM） and 3-methacryloxypropyltrimethoxysilane （MPTMS）. The copolymers were then crosslinked through hydrolysis of the siloxane in acetic acid/water mixed solvent. Beta-cyclodextrin （Beta-CD） was introduced into the polymeric networks by condensation of 3-glycidoxypropyltrimethoxysilane derived beta-cyclodextrin （KH560-beta-CD） with MPTMS under acidic condition. These gels were heterogeneous, porous and exhibited fast deswelling kinetics when the temperature was elevated to above lower critical solution temperature （LCST）. The swelling ratios of the gels containing beta-CD at room temperature were higher than that of the normal PNIPAM hydrogel, which was caused by the lower crosslinking density in beta-CD contained gels. In comparison to that of the normal PNIPAM gel, the amount of loaded-drug in the hydrogel containing beta-CD was higher, and the release time of 5-fluorouracil （5-Fu） was prolonged, which was attributed to the formation of inclusion compounds between 5-Fu and beta-CD in gel network.

THE ■-STATE OF A SINGLE HOMOPOLYMER CHAIN IN SOLUTION

It has been an established practice to estimate the Θ-temperature of a polymer solution from thedisappearance of the interchain interactions (A_2 = 0) Recently, in studies of the temperature dependence ofthe chain conformation in solution, we found that the change of the chain conformation clearly underwentthree different stages which could be viewed as the 'gas'. 'liquid' and 'solid' states in terms of the freedomof the 'blobs' on the chain. The transition temperature between the first and second stages corresponds nicelyto the Θ-temperature determined by the conventional method. It reveals, for the first time, that the Θ-temperature can be deduced from the conformation change of a single polymer chain in solution, which isimportant not only in conception, but also in practice.