STABILITY OF POLY(N,N''''-METHYLENEBISACRYLAMIDE-co-4-VINYLPYRIDINE)MICROGEL DISPERSION AND ADJUSTMENT OF THE HYDROPHOBICITY IN THE MICROGELS

In the UV-Vis spectra of pure light-scattering systems,there is an exponential relationship between absorbance and wavelength(A=Kλ~(-n)).Here,the exponent n is named as flocculation-coagulation parameter.In the present paper,the effects of different additives on the stability of poly(N,N'-methylenebisacrylamide-co-4-vinylpyridine)(poly(Bis-co-4-VP)) microgel dispersion were studied in detail via this parameter.The results showed that the stability of the dispersion mainly comes from the ionization of pyridine groups,making the microgel positively charged on its surface.This was confirmed by the measurement of Zeta potential and the result of conductometric titration.The result of fluorescence analysis indicated that the hydrophobicity in the microgels is enhanced with the increase in total 4-VP unit content.     

EFFECTS OF L-PHENYLALANINE ON THE RADIATION SYNTHESIS OF POLY （N,N＇-METHYLENEBIS A CR YLAMIDE-co-4-VINYLPYRID INE） （MICRO）GELS

The effects of L-phenylalanine （L-Phe） on the synthesis ofpoly（N,N＇-methylenebisacrylamide-co-4-vinylpyridine） （poly（Bis-co-4-VP）） （micro）gels by γ-ray irradiation were studied. The addition of L-Phe could not only decrease the gelation dose （Dg） of the synthesis obviously, but also transform the morphology of copolymer from microgel to gel. In addition, the swelling ability of the （micro）gels was also affected in the presence of L-Phe. The decrease of Dg was ascribed to the effect of pH, while the transformation of the morphology was ascribed to the effect of L-Phe on the stability of the poly（Bis-co-4-VP） microgel. Such an effect was confirmed further as compared with the effects of L-alanine, L-glutamic acid, L-arginine, sulfuric acid and aqueous ammonia.     

EFFECTS OF L-PHENYLALANINE ON THE RADIATION SYNTHESIS OF POLY(N,N''''-METHYLENEBISACRYLAMIDE-co-4-VINYLPYRIDINE)(MICRO)GELS

The effects of L-phenylalanine(L-Phe)on the synthesis of poly(N,N'-methylenebisacrylamide-co-4-vinylpyridine) (poly(Bis-co-4-VP))(micro)gels by γ-ray irradiation were studied.The addition of L-Phe could not only decrease the gelation dose(D_g)of the synthesis obviously,but also transform the morphology of copolymer from microgel to gel.In addition,the swelling ability of the(micro)gels was also affected in the presence of L-Phe.The decrease of D_g was ascribed to the effect of pH,while the transformation of the morphology was ascribed to the effect of L-Phe on the stability of the poly(Bis-co-4-VP)microgel.Such an effect was confirmed further as compared with the effects of L-alanine,L-glutamic acid,L-arginine,sulfuric acid and aqueous ammonia.     

SUPPRESSION OF CELL ADHESION ON POLYACRYLONITRILE-BASED MEMBRANES BY THE ANCHORING OF PHOSPHOLIPID MOIETIES

In this work, the membrane surface of poly（acrylonitrile-co-2-hydroxyethyl methacrylate） （PANCHEMA） was chemically modified by anchoring of phospholipid moieties. The process involved the reaction of hydroxyl groups on the membrane surface with 2-chloro-2-oxo-1,3,2-dioxaphospholane （COP） followed by the ring-opening reaction of COP with trimethylamine. Chemical differences between the original and the modified membranes were characterized by FT-IR and XPS, It was found that the amount of macrophage adhered on the modified membrane surface is substantially lower than that on polyacrylonitrile （PAN） and PANCHEMA membranes under the same condition, The morphological change of the adherent cell is also suppressed by the generation ofphospholipid moieties on the membrane surface.     

DISPERSION STATE OF ZINC OXIDE ON SURFACE OF SILICA GEL AND SURFACE ACIDITY OF ZnO/SiO_2

The dispersion threshold level of zinc oxide on silica gel was determined by X-ray quantitative phase analysis. And the results of XPS experiments show that the surface of the sample is enriched with ZnO and there is a limit for the ZnO amount dispersed on the surface. The value of this limit is corresponding with the threshold level obtained by XRD. The measurements of surfaee acidity show that there are some stronger acid sites on the surface of ZnO/SiO_2, they have not been found on the ZnO or SiO_2 individually, and the total amount of acid increases remarkably. The acidity depends on the ZnO concentration in the surface phase and reaches the maximum at the threshold value.In this paper, we propose a new point of view for the origin of the acidity on surface of the ZnO/SiO_2 samples. ZnO is well dispersed on the surface of SiO_2 gel in a monolayer state. In this situation, some new surface structure units emerge as a result of interaction between dispersed ZnO and the carrier, which are responsible     

CRYSTALLIZATION AND MECHANICAL PROPERTIES OF POLYPROPYLENE FILLED WITH SiO2 NANOPARTICLES

Oleic acid （OA）-modified SiO2 （OA-m-SiO2） nanoparticles were prepared using surface modification method. Infrared spectroscopy （IR） was used to investigate the structure of the OA-m-SiO2 nanoparticles, and the result showed that OA attached onto the surface of SiO2 nanoparticles through esterification. Effect of OA concentration on the dispersion stability of OA-m-SiO2 in heptane was also studied, and the result indicated that OA-m-SiO2 nanoparticles were dispersed in heptane more stably than the unmodified ones. OA-m-SiO2 nanoparticles can also be dispersed in polypropylene （PP） matrix in nano-scale. The effect of OA-m-SiO2 on crystallization of PP was studied by means of DSC. It was found that the introduction of OA-m-SiO2 resulted in significant increase in the crystallization temperature, crystallization degree and crystallization rate of PP, and OA-m-SiO2 could effectively induce the formation of β-crystal PP. Effect of OA-m-SiO2 content on mechanical properties of PP/OA-m-SiO2 nanocomposites was also studied. The results show that OA-m-SiO2 can significantly improve the mechanical properties of PP.     

A STUDY ON THE STRUCTURE AND PROPERTIES OF POLYBUTYLALDEHYDE FORMED IN LOW TEMPERATURE PLASMA

The polybutylaldehyde obtained by plasma polymerization was investigated by means of IR, X-ray diffraction, GC-MS, elementary analysis, TEM, electron diffraction and contact angle measurements etc. The results showed that the polymer formed in plasma is amorphous crosslinked polymer, and its backbone is made of carbon atoms. The surface energy of the polymer film is independent of the polymerization conditions. No addition reaction has taken place in the carbonyl group of butylaldehyde in the plasma condition. The result of the wettability measurements showed that the polymer film is generally hydrophobic and the surface energy of the film is about 41 dyn/cm, in which the dispersion force contribution is the majority. The electron diffraction proved that some crystal substance, even the single crystals were present in the polymer. X-ray diffraction also proved the presence of crystal and showed about 15% crystaUinity fraction.     

Fabrication of Poly（4-vinylpyridine） Nanofiber and Fluorescent Poly（4-vinylpyridine）/Porphyrin Nanofiber by Electrospinning

Poly（4-vinylpyridine）（P4-VP） nanofiber and fluoresent poly（4-vinylpyridine）/porphyrin（P4-VP/TPPA） nanofiber were respectively prepared by electrospinning. The effect of the concentration of P4-VP/dimethylformamide （DMF） electrospinning solutions on the morphology of P4-VP nanofiber was investigated and it was found that the average diameter of the nanofiber of P4-VP/DMF increased with the increase of the concentration of the spinning solution. After the addition of TPPA to the P4-VP/DMF spinning solution, the diameter of P4-VP/TPPA nanofiber became even due to the increase of the conductivity of the P4-VP/DMF-TPPA solution. The photoluminescent（PL） spectral analysis indicates that the emission peak position of P4-VP/TPPA nanofiber is almost the same as that of pure TPPA at about 650 nm without peak shift, and when it was stored for 20 days, the emission peak of P4-VP/TPPA nanofiber is also at 650 nm, indicating that the fluorescent property of P4-VP/TPPA nanofiber is stable. Fourier-transform iufrared（FTIR） spectrum confirms the chemical composition of the resulting P4-VP/TPPA composite nanofiber.     

STUDY ON STABILITY OF STRUCTURE AND PROPERTIES OF TIOPC/SAN PHOTOCONDUCTIVE COMPOSITES

The influence of the condensed structure of poly(styrene-co-acrylonitrile) (SAN) and traces of tetrahydrofuran(THF) that remained in titanyl phthalocyanine (TiOPc)/SAN films after fabrication on the photoconductive stability ofTiOPc/SAN composites is studied. The results reveal that the existence of traces of THF results in the increase of thephotoconductivity and the charging voltage. The main facors responsible for the unstable photoconductivity of thephotoconductors are believed to be the relaxation of SAN and the slow volatilization of THF.     

THE EFFECT OF MODIFICATION OF COORDINATING GROUPS ON THE CATALYTIC BEHAVIORS OF POLYMER CATALYSTS

Several polymer-supported palladium complex catalysts containing two different coordinatinggroups were prepared and the cooperative effect of the coordinating groups on the catalytic behaviorsof polymer catalysts was studied. It was found that poly(acrylic acid-co-acrylonitrile)-Pd complex(PAA-AN-Pd) is a more active and stable catalyst for hydrogenation than both poly(acrylic acid)-Pd and poly(acrylonitrile)-Pd complexes. A marked change of catalytic behaviors of poly(N-substituted maleamic acid-co-styrene)-Pd complexes was observed in comparison with poly(maleicacid-co-styrene)-Pd complex. Acetophenone was reduced to 1-phenyl ethanol by poly(N-phenylmaleamic acid-Co-styrene)-Pd complex (N-1-Pd), but ethylbenzene was obtained using poly(maleicacid-co-styrene)-Pd complex as a catalyst. The influence of solvents, additives and N/Pd gramatomic ratio on the catalytic behaviors of the polymer complexes was investigated.     

Isothermal titration calorimetric studies of the acid-base properties of poly(N-isopropylacrylamide-co-4-vinylpyridine) cationic polyelectrolyte colloidal microgels

Isothermal titration calorimetry (ITC) and potentiometric titration were used to study the protonation properties of the 4-vinylpyridine (4-VP) moiety in cationic poly(N-isopropylacrylamide-co-4-vinylpyridine) colloidal microgels [poly(NIPAM-co-4-VP)]. Calorimetric pH titrations were performed using microgels of different 4-VP content and the influence of ionic strength and counter ions have been examined. The calorimetric titration output consists of several thermal contributions reflecting the complex nature of the interactions in the aqueous microgel dispersions. In contrast to the potentiometric results, the calorimetric titration data could not be completely described by a theoretical model solely taking into account protonation equilibria. Deviations from the proposed model correlate with swelling or shrinking of the gel particles. The calorimetric results also reveal a pronounced counter-ion effect of perchlorate compared to chloride ions. In the presence of perchlorate ions, small secondary thermal effects accompany protonation of the 4-VP moiety due, in part, to kinetically limited conformational changes in the co-polymer microgel.     

Preparation of raspberry-like nanocapsules by the combination of Pickering emulsification and solvent displacement technique

Well-defined raspberry-like nanocapsules were prepared by the combination of Pickering emulsification and solvent displacement technique by using silica particles as stabilizer and hexadecane (HD) as soft template. The formation of the capsule morphology is caused by the phase separation of poly(styrene-co-4-vinyl pyridine) (poly(St-co-4-VP)) in the droplets due to the diffusion of good solvent for the (co)polymer to the aqueous continuous phase. The size of capsules was successfully reduced from tens of micrometers in the dispersion by simply stirring to the nanorange by the employment of sonication and Ostwald ripening. The formation of silica-particles-armored nanocapsules was confirmed by transmission electron microscopy (TEM), high-resolution scanning electron microscopy (HRSEM), dynamic light scattering (DLS), and zeta potential measurement. The colloidal stability and particle properties, including size and morphology, depend on the amount of HD, and copolymers, the sonication time, the dispersion pH value, the type of solvent, and the copolymer composition.     

Colored thin films prepared from hydrogel microspheres

Ordered 2-D structures composed of poly(N-isopropylacrylamide) (PNIPAM) microgel particles that had regularity on a sub-micrometer length scale were prepared. By using sterically stabilized PNIPAM microgel particles as components, the ordered array was formed by a self-assembly process. The particle array was prepared by depositing a droplet of the microgel dispersion on a substrate. Atomic force microscopy observation of the resulting thin films revealed that they comprised a monolayer particle array. The periodic structure of the array produced iridescent colors due to optical diffraction. Since a homogeneous particle array can be prepared simply by drying the dispersion, this particle dispersion may be considered as a new ink whose color is generated from the microstructure in the films produced.     

Absorption of cetylpyridinium chloride into poly(N-isopropylacrylamide)-based microgel particles, in dispersion and as surface-deposited monolayers

The addition of cetylpyridinium chloride (CPC) to aqueous dispersions of poly(N-isopropylacrylamide) [poly(NIPAM)] and poly(N-isopropylacrylamide-co-acrylic acid) [poly(NIPAM-co-AAc)] microgel particles leads to absorption of the CPC into the particles and to corresponding changes in their hydrodynamic diameter. With the latter set of particles there is a strong pH dependence. The dependence of both hydrodynamic diameter and electrophoretic mobility of the microgel particles on the added CPC concentration show a strong correlation with CPC uptake, as obtained from direct CPC absorption measurements. Various mechanisms for CPC absorption into the microgel particles are postulated, including electrostatic, polar, and hydrophobic interactions. A comparison has also been made between the effect of added CPC on the hydrodynamic diameter of free microgel particles in dispersion, determined by dynamic light scattering, and the thickness of adsorbed monolayers of the same microgel particles deposited on cationically modified, oxidized silicon surfaces, as determined from ellipsometry measurements. The trends observed in both cases are broadly similar. This work opens the way for development of microgel layers for controlled uptake and release applications.     

On the structure of poly(N-isopropylacrylamide) microgel particles

This investigation presents a study of the internal structure of poly(NIPAM/xBA) microgel particles (NIPAM and BA are N-isopropylacrylamide and N,N'-methylene bisacrylamide, respectively). In this study, x is the wt % of BA used during microgel synthesis. Two values of x were used to prepare the microgels, 1 and 10. The microgel dispersions were investigated using photon correlation spectroscopy (PCS) and small-angle neutron scattering (SANS). These measurements were made as a function of temperature in the range 30-50 degrees C. Scattering maxima were observed for the microgels when the dispersion temperatures were less than their volume phase transition temperatures. The SANS data were fitted using a model which consisted of Porod and Ornstein-Zernike form factors. The analysis showed that the macroscopic hydrodynamic diameter of the microgel particles and the submicroscopic mesh size of the network are linearly related. This is the first study to demonstrate affine swelling for poly(NIPAM/xBA) microgels. Furthermore, the mesh size does not appear to be strongly affected by x. The data suggest that the swollen particles have a mostly homogeneous structure, although evidence for a thin, low segment density shell is presented. The study confirms that poly(NIPAM/xBA) microgel particles have a core-shell structure. The shell has an average thickness of approximately 20 nm for poly(NIPAM/1BA) particles which appears to be independent of temperature over the range studied. The analysis suggests that the particles contained approximately 50 vol % water at 50 degrees C. The molar mass of the poly(NIPAM/1BA) microgel particles was estimated as 6 x 10(9) g mol(-1).     

Preparation of organic-inorganic composite anion-exchange membranes via aqueous dispersion polymerization and their characterization

Organic-inorganic composite membranes based on poly(vinyl alcohol)/SiO(2) were prepared via an aqueous dispersion polymerization route and anion-exchange groups were introduced in the membrane matrix by the chemical grafting of 4-vinylpyridine with the desired content. These membranes were extensively characterized for their surface morphology, thermal stability, water content, and surface-charge properties using SEM, TEM, FTIR, TGA, water uptake, and ion-exchange capacity measurements. Counterion transport numbers across these membranes were estimated from membrane potential data. Membrane conductance measurements were also performed and these data were used for the estimation of values of counterion diffusion coefficients in the membrane phase. Physicochemical and electrochemical properties of these membranes and equivalent pore radius (estimated from electroosmotic flux measurements) were found to be highly dependent on the 4-vinylpyridine (4-VP) content in the membrane phase. It was also observed that for better selectivity and membrane conductivity of anion-exchange membranes complete optimization of the loading of 4-VP in the membrane phase is necessary. Furthermore, among these, membrane with 25% loading with 4-VP exhibited very good selectivity, water content, and ion-exchange capacity along with moderate membrane conductivity, which may be used for their application in electro-driven separation at elevated temperatures or for other electrochemical processes.     

Electrical switching of microgel swelling and collapse for display applications

We investigate whether a high‐contrast electronic paper can be formed using a microgel dispersion in which the particles reversibly swell and collapse on cycling the pH. An aqueous dispersion of particles of poly(2‐vinylpyridine) crosslinked with divinylbenzene is studied. It is demonstrated that the pH of the dispersion, and hence the state of the microgel particles, can be potentiostatically controlled using a polyaniline electrode. Electrochemical switching of the dispersion from highly scattering to transparent for all visible wavelengths is achieved. Modification of cell and electrode design is required to reduce the switching time, presently greater than 10 min. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012