Henmei Ni

Preparation of pH-sensitive nanoparticles of poly (methacrylic acid) (PMAA)/poly (vinyl pyrrolidone) (PVP) by ATRP-template miniemulsion polymerization in the aqueous solution

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).

ATRP-template dispersion polymerization of methacrylic Acid/PVP

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.

Partition of initiators in quasi-static precipitation polymerization of AAm/MAc

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.

Charges of soluble amphiphiles and particles: random and diblock copolymerizations of MAA/AAm, MAA/St, and MAA/4VP in ethanol

AbstractRandom 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. FigureIn ethanol, the soluble diblock copolymers of P(MAA-co-X) (X = AAm, St) and particles of P(MAA-co-4VP) were positively charged, though the component of MAA was dominant. The particles of P(MAA/AAm) were negatively charged and particles of P(MAA-co-St) were charge neutrality. The soluble random copolymers generally were charge neutrality. It was relatively difficult to prepare particles by random copolymerization. These results indicated that the electrostatic interactions played an important role on the self-assembly and particle formation

Preparation of a poly(DMAEMA-co-HEMA) self-supporting microfiltration membrane with high anionic permselectivity by electrospinning

Abstract A cross-linked microfibrous anion exchange membrane with high ion permselectivity and robust mechanical properties was fabricated by electrospinning. Copolymer, poly N,N-dimethylaminoethyl methacrylate (DMAEMA)-co-2-hydroxyethyl methacrylate (HEMA), was selected as the electrospun material. Fourier transform infrared (FTIR) spectroscopy, 1HNMR and scanning electron microscopy (SEM) were employed to characterize the copolymer and microfibrous mat. The electrospinning optimal parameters were determined by orthogonal experiments. Formaldehyde vapor was applied to crosslink the mat. It was observed that the water sorption decreased from 75.7% to 30.4% as the crosslinking time increased from 20 h to 32 h. The robust mat with the high tensile strength of 4.62 MPa and 50% elongation at break was obtained at 24 h. The ion permeability of NO3−, Cl−, SO42− were 94, 91 and 87%.

Three dimension Liesegang rings of calcium hydrophosphate in gelatin

Three dimensional Liesegang spherical layers of CaHPO4 in gelatin ball were performed by employing CaCl2 and Na2HPO4 as the inner and outer electrolyte, respectively. Effects of concentrations of inner and outer electrolyte as well as pH on the morphologies of Liesegang rings (LRs) were investigated. As a result, it was observed that the time law, spacing law and width law found in 1D/2D gel systems were obeyed in this 3D gelatin system. The interaction of Ca2+ and HPO42− with gelatin matrix played a key role to the formation of LRs due to the existence of carboxylic groups on the gelatin chains. Using Ca2+ as the inner electrolyte, LRs were prepared. However, employing HPO42− as inner electrolyte, LRs were not obtained. Moreover, pH of gelatin solution greatly impacted on the formation of LRs. The number of LRs increased with the decrease of pH, whereas the width inversely decreased. pH 4.40 was a turn point, from which the spacing coefficient abruptly increased as pH increased. All these results indicated that the network was created by the interaction of Ca2+ and –COO− of gelatin chains, which dominated the formation of CaHPO4 LRs in gelatin.

PMAA-based RAFT dispersion polymerization of MMA in ethanol: conductivity, block length and self-assembly

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.