Co-reporter:Henmei Ni, Junxiu Liu, Kai Shi, Min Wu, Yadong Yang and Lijuan Zhang
RSC Advances 2016 vol. 6(Issue 63) pp:58218-58225
Publication Date(Web):10 Jun 2016
DOI:10.1039/C6RA09895A
The reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of methyl methacrylate (MMA) was carried out in ethanol using polymethacrylic acid (PMAA)–4-cyanopentanoic acid dithiobenzoate (CADB) (degree of polymerization = 30, 122 and 450) as a macro chain transfer agent (CTA) and 2,2′-azobis(2,4-diemthyl valeronitrile) (V-65) as an initiator. In contrast to the random copolymerization systems, a dramatic increase of conductivity during the initial stage of RAFT polymerization was observed. It was confirmed that the conductivity resulted from the charged solvophobic blocks of soluble diblock copolymers, strongly dependent on the chain length of PMAA-CTA and PMMA. Objects of PMAA-b-PMMA were prepared by three methods, i.e. the polymerization-, temperature- and ion-induced self-assembly. The procedure of self-assembly commonly resulted in a dramatic decrease of conductivity. All results indicated that the electrostatic interaction played a role in the process of self-assembly, rather than just the solvophobic interaction of PMMA blocks in ethanol.
Co-reporter:Meiling Liang, Weijie Li, Qi Qi, Pingchuan Zeng, Yucheng Zhou, Yingping Zheng, Min Wu and Henmei Ni
RSC Advances 2016 vol. 6(Issue 7) pp:5677-5687
Publication Date(Web):02 Dec 2015
DOI:10.1039/C5RA20481J
A three-component metal catalyst was prepared and used in the process of catalytic wet peroxide oxidation (CWPO) for the degradation of unsymmetrical dimethylhydrazine (UDMH) in propellant wastewater with H2O2. It was structurally characterized using scanning electron spectroscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX), and its catalytic activity was evaluated using indexes such as the efficiency of UDMH degradation and chemical oxygen demand (COD) removal and the concentrations of ammonia (NH3–N), formaldehyde (HCHO), total nitrogen (TN), total organic carbon (TOC) and N-nitrosodimethylamine (NDMA). Besides, the reaction system was monitored using UV-Vis full wavelength scanning spectroscopy and liquid chromatography-mass spectroscopy (LC-MS). As a result, it was observed that the degradation mechanism involved ˙OH attacking the amino group and homocoupling in UDMH with the simultaneous transformation of the active component CuII/I. Based on investigation of the reaction factors (H2O2 dosage, temperature, catalyst dosage, pH and initial concentration of UDMH) focusing on the removal of NDMA, the optimal conditions for CWPO with a three-component metal catalyst were determined. The high treatable concentration of UDMH (500 mg L−1), rapid rate and good reusability with a high efficiency of UDMH degradation and COD removal (99.9% in 10 min and 94.6% in 30 min, respectively) and the low concentration of NDMA are merits of the present catalyst.
Co-reporter:Guoxia Chen;Junxiu Liu;Yadong Yang;Lijuan Zhang;Min Wu
Colloid and Polymer Science 2015 Volume 293( Issue 7) pp:2035-2044
Publication Date(Web):2015 July
DOI:10.1007/s00396-015-3554-3
Employing polymethacrylic acid (PMAA) as the template and N-vinyl pyrrolidone (N-VP) as monomer, the ATRP-template miniemulsion polymerization was carried out in the aqueous medium by using MBP/CuBr/bpy as initiator. The results were characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), and gel permeation chromatography (GPC). It was observed that the stable particles exhibited amphoteric pH sensitivity, namely that in the range of pH 3.0 to 5.0, the particles precipitated, whereas beyond the range the particles were stable and swollen as pH varied. Moreover, the pH range was variable according to the molecular weight of PVP. The results of GPC indicated that the molecular weight of template polymer PMAA was duplicated by the daughter polymer PVP. Being noncross-linked, unlike the common microgels, the hydrodynamic diameter dramatically increased in a very narrow pH range, e.g., pH 5.5 –6 and 2.0–2.5. Finally, the nanoparticles of PMAA/PVP were applied for the controlled release of rifampicin (RFP) and doxorubicin (DOX).
Co-reporter:Yulu Chen;Yimeng Cui;Yuanshan Jia;Kan Zhan;Hui Zhang;Guoxia Chen;Yadong Yang;Min Wu
Journal of Applied Polymer Science 2014 Volume 131( Issue 17) pp:
Publication Date(Web):
DOI:10.1002/app.40716
ABSTRACT
Conjugate electrospinning of two nozzles with opposite charges was used for the fabrication of charged mosaic membrane (CM membrane). Sodium polystyrene sulfonate (PNaSS) and poly(4-vinyl pyridine) (P4VP) were selected as anionic and cationic exchange elements, respectively. Polyvinyl alcohol was used as the common matrix for the enhancement of mechanical properties by formaldehyde crosslinking. Scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile testing for nanofiber were used for the characterizations of CM membrane. Using the conjugate electrospinning, a simple equation was established to predict the mean diameters of nanofibers. It was proved that the calculated diameters fit well with the experimental data using electrospinning parameters such as concentration of spun solution, collecting speed, rate of solution supply, and distance of two nozzles. TEM picture showed a PNaSS nanofiber was incorporated with a P4VP nanofiber. However, SEM photo indicated that the alignment of composite nanofibers in CM membrane was greatly affected by the concentration of polyelectrolyte. As the concentration of PNaSS increased, the alignment degree decreased. After crosslinking with formaldehyde for 20 h, the tensile strength and Young's modulus of CM membrane reached 11.3 and 24.8 MPa, respectively. The water content and water insolubility of CM membrane were also investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40716.
Co-reporter:Kan Zhan;Hui Zhang;Min Li;Yulu Chen;Guoxia Chen
Colloid and Polymer Science 2014 Volume 292( Issue 7) pp:1553-1565
Publication Date(Web):2014 July
DOI:10.1007/s00396-014-3215-y
Random and reversible addition-fragmentation chain transfer (RAFT) copolymerizations of methacrylic acid (MAA)/acrylamide (AAm), MAA/styrene (St), and MAA/4-vinyl pyridine (4VP) were carried out in ethanol. (CPDB)-terminated PMAA (PMAA-CPDB) and 2,2′-azobis(2,4-diemthylvaleronitrile) (V-65) was used as the macromolecular chain transfer agent (CTA) and initiator, respectively. Electric conductivity of copolymerization systems was traced throughout the polymerizations, and charges of soluble copolymer and particles were detected. As a result, a considerable increase of conductivity was observed in all of the RAFT polymerization systems, whereas the variation of conductivity in the random copolymerization systems was insignificant. The high conductivity of RAFT polymerization was dominantly contributed by the soluble diblock copolymers in the serum, rather than their particles, except for P(MAA-b-4VP) where only the particles was obtained due to the zwitterionic interactions of PMAA segments and 4VP. In the direct current (DC) field, the behavior of these soluble diblock copolymers, P(MAA-b-AAM) and P(MAA-b-St), indicated that they were positively charged, whereas the particles of (PMAA-b-AAm) and P(MAA-b-4VP) were surprisingly negatively charged, though the composition of MAA was dominant. Soluble random copolymers of P(MAA-co-St) and P(MAA-co-4VP) represented the charge neutrality. These results indicated that the positive charges were contributed by the solvophobic block in the soluble diblock copolymers. Therefore, the diblock copolymers were the macrodipoles boosting the conductivity of solution. Meanwhile, it indicated that the electrostatic interactions of dipoles were possibly the main driving force of their self-assembly. Generally, compared with RAFT polymerization, the particles were hard to be prepared in the random copolymerization. It implies that the electrostatic interactions of diblock copolymers also played an important role in the particle formation.
Co-reporter:Hen-mei Ni 倪恨美;Hui Zhang;Guo-xia Chen;Jun-xiu Liu
Chinese Journal of Polymer Science 2014 Volume 32( Issue 10) pp:1400-1412
Publication Date(Web):2014 October
DOI:10.1007/s10118-014-1498-6
In order to investigate the partition of initiators for quasi-static precipitation polymerization of acrylamide (AAm) and methacrylic acid (MAc) in ethanol, azo-initiators were employed with various functional groups such as —COOCH3 (V-601, dimethyl 2,2′-azobis(isobutyrate)), — CN (V-65, 2,2′-Azobis(2,4-diemthylvaleronitrile)), — COOH (V-501, 4,4′-azobis(4-cyanovaleric acid)) and —NH-(VA-061, 2,2′-azobis[2-(2-imidazolin-2-yl)propane]), respectively. Particle size, induction time and kinetics of polymerization were investigated by the scanning electron microscopy (SEM) and gravimetry. It was observed that the polymerization parameters, such as the particle size, induction time and polymerization rate, were considerably affected by the functional groups of initiators. Besides, the monomer concentration also played important roles in the particle formation. By using V-601, the polymerization rate was strongly correlated with the total surface area of particles and the concentration of initiators. However, by using V-501, the polymerization rate was strongly related to W0Ci,0, where W0 is the initial concentration of monomers and Ci,0, the initial concentration of initiators. The results indicated that the different functional groups determined the different partition types of initiators between the minimonomer droplets and the continuous phase due to the molecular interactions of initiator and monomers. V-601 was all partitioned in the continuous phase, but a part of V-65 was partitioned in the minimonomer droplets. Besides the V-501 dissolved in the continuous phase, a part of V-501 was adsorbed on the surface of minimonomer droplets. VA-061 destroyed the stability of minimonomer droplets by the formation of zwitterions with MAA.
Co-reporter:Cheng-cheng Yang;Dan Meng;Kan Zhan;Yu-lu Chen
Chinese Journal of Polymer Science 2014 Volume 32( Issue 4) pp:476-487
Publication Date(Web):2014 April
DOI:10.1007/s10118-014-1431-z
ATRP-template dispersion polymerization of methacrylic acid (MAA) on the template of polyvinyl pyrrolidone (PVP K-30) was carried out in the aqueous solution by using methyl 2-bromopropionate (MBP)/CuCl/2,2′-bipyridine (bpy) as the initiation system. The scanning electron microscopy (SEM), dynamic light scattering (DLS) and gel permeation chromatography (GPC) were employed for evaluating the results of polymerization. As a result, the minimonomer droplets formed due to the H-bond interaction of PVP-MAA. The stability of droplets was dependent on pH and the concentrations of both PVP and MAA. When pH < 2, the coagulum of PVP-MAA formed, whereas when pH > 4.5, the droplets were not observable by DLS. In order to prepare the stable latex, the concentration of PVP should be lower than 9 wt%, whilst the concentration of MAA should be lower than 5.5 wt%. The optimum condition was pH 2.4, PVP 4.76 wt% and MAA 5 wt%, by which the stable latex of ca. 50 nm nanoparticles of PMAA/PVP was prepared by ATRP polymerization and simultaneously the molar mass of PVP was duplicated by PMAA according to GPC diagrams. In contrast, by using AIBN, KPS and KPS-Na2SO3 redox initiation system, the coagulum accompanying with the larger molar mass of PMAA was obtained, irrespective of pH and concentrations of PVP and MAA.
Co-reporter:Ni Henmei, Min Wu, Min Li, Hualin Wang and Yueming Sun
Polymer Chemistry 2010 vol. 1(Issue 6) pp:899-907
Publication Date(Web):10 Mar 2010
DOI:10.1039/C0PY00017E
Quasi-static precipitation polymerization of acrylamide (AAm) and methacrylic acid (MAc) in ethanol by using 2,2′-azobis(2,4-diemthylvaleronitrile) (V-65) as initiator was carried out. The effects of initial concentration of initiator and monomers on the kinetics of polymerization were investigated by gravimetry, SEM and HPLC. It was observed that the number of particles was severely dependent on the total initial concentration of monomers, and less affected by the concentration of initiator. The total surface area of the particles was independent of the concentration of initiator, but slightly affected by the initial concentration of monomers. In the range investigated in this paper, the lowest initial concentration of monomers, gave the maximum number of particles, whilst the highest concentration gave the minimum number of particles, but there was no significant difference observed among the total surface area of particles prepared by using various monomer concentrations. The normalized diameter against the initial concentration of monomers was linearly simulated in the range of concentration of monomers, W0, investigated in present system, R′ = 75.4W0 + 149.5. After the induction period, several pairs of curves of conversion vs. polymerization time overlapped. It indicated that the variation of conversion against time mathematically related to , where Ci,0 was the initial concentration of initiator. HPLC revealed MAc was consumed faster than AAm during the polymerization and a lot of AAm remained in dry particles.
Co-reporter:Henmei Ni;Haruma Kawaguchi;Takeshi Endo
Colloid and Polymer Science 2007 Volume 285( Issue 7) pp:819-826
Publication Date(Web):2007 April
DOI:10.1007/s00396-006-1631-3
Monodisperse hydrogel microsphere of polyacrylamide (AAm)-methacrylic acid (MAc) cross-linked by N,N′-methylene-bis(acrylamide) (MB) with sharp pH–volume transition was prepared in ethanol. The dynamic light scattering (DLS) was employed to evaluate the pH sensitivity of these microspheres. The effects of main factors: composition of copolymer, cross-linked degree, and initial total concentration or solid content of comonomers were investigated. Osmotic pressure and deformation of cross-linked polymer network were considered as the two dominant factors influencing the characteristics of pH–volume transition. High content of MAc and cross-linked degree increased the osmotic pressure, thereby moving the onset of pH–volume transition to higher pH. Association/dissociation of poly-MAc segments in the domains contributed to the free energy of hydrogel–solvent mixing. As soon as pH was high enough to overcome the osmotic pressure, the dissociated poly-MAc segments simultaneously decreased the osmotic pressure and free energy of hydrogel–solvent mixing, thereby allowing the sharp and large volume transition. As a result, microspheres were prepared with pH–volume transition of almost 12 times to their original volume within a narrow range of pH variation, ca. 0.5.
Co-reporter:Henmei Ni;Haruma Kawaguchi;Takeshi Endo
Colloid and Polymer Science 2007 Volume 285( Issue 8) pp:873-879
Publication Date(Web):2007 May
DOI:10.1007/s00396-006-1633-1
The forming process and characteristics of monodispersed hydrogel microspheres of poly(acrylamide–methacrylic acid) with sharp pH–volume transition were studied. pH-/ion-sensitive and thermosensitive behaviors of microspheres sampled at various stage of polymerization were evaluated by using the dynamic light scattering. It was observed that the sharpness of pH–volume transition increased with the increase in monomer conversion. Both thermo- and ion-sensitive behaviors were affected by pH. At pH 4.3, the hydrodynamic diameter of microspheres monotonically and slightly decreased with the increase in temperature, whereas at pH 3.5 and 3.8, the curves of thermo–volume transition were similar to those of pH–volume transition with a maximum temperature at 25 and 20 °C, respectively. Increasing the [CaCl2] was to decrease the hydrodynamic diameters of microspheres, irrespective of pH. However, a region at lower [NaCl] was found, where the diameter increased with the increase in [NaCl]. Moreover, the range of diameter increasing extended to higher [NaCl] as pH increased.
Co-reporter:Henmei Ni;Haruma Kawaguchi
Journal of Polymer Science Part A: Polymer Chemistry 2004 Volume 42(Issue 11) pp:2833-2844
Publication Date(Web):28 APR 2004
DOI:10.1002/pola.20089
We previously established a new mechanism of monodispersed poly(acrylamide/methacrylic acid) (PAAm/MAA) microspheres on the basis that the minimonomer droplets of AAm/MAA complexes were formed in ethanol at a polymerization temperature of 60 °C prior to the polymerization. Here, the effects of various factors such as the types and amount of initiators and crosslinking agents on the average diameters and morphologies of PAAm/MAA microspheres were qualitatively discussed on the basis of the new mechanism. The partition of reagents between the minimonomer droplets and the continuous medium was particularly emphasized in discussion because the formation of microspheres occurred in the minimonomer droplets. The new mechanism suggested that the size (number) and morphologies of the microspheres as well as the polymerization kinetics were consequently dependent on the properties and amount of initiators, crosslinking agents, and other monomers. It successfully explained the experimental phenomenon observed thus far in precipitation or dispersion polymerizations that the average diameter of microspheres is increased with the increase of the concentration of initiators, which contradicted the prediction of conventional mechanisms. As an example, the initiator dimethyl 2,2′-azobisisobutyrate (DMAIB) was dominantly partitioned in ethanol. Thus, the diameter of the PAAm/MAA microspheres was decreased with the increase of the concentration of DMAIB because the formation of microspheres depended on the adsorption of free radicals to the minimonomer droplets. However, the initiator 4,4′-azobis-4-cyanovaleric acid was dominantly partitioned within the minimonomer droplets, thereby increasing the diameter of the microspheres as the concentration of initiator was increased because of the lower efficiency of free radicals. Relative to the initiators, the crosslinking agents showed inverse effects on the diameter and morphology of the microspheres according to the different partitions. The monomer was transferred by the incorporation of minimonomer droplets with growing microspheres. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2833–2844, 2004
