Preparation of poly(vinyl alcohol)/poly(acrylic acid) microcapsules and microspheres and their pH-responsive release behavior

The pH-responsive poly(vinyl alcohol)/poly(acrylic acid) hydrogel microparticles containing vitamin B₁₂ were prepared with emulsion polymerization. Both microcapsule and microsphere were easily produced by simply changing the sequence of ingredient addition during the emulsion polymerization. The microparticles showed the faster and larger release of vitamin B₁₂ due to the higher swelling of hydrogel by electrostatic repulsion of carboxylate groups in poly(acrylic acid) as the pH was changed into more basic condition. The microcapsules showed a faster release than the microspheres did due to the less hindered passage through the thinner shell of microcapsules. The poly(vinyl alcohol)/poly(acrylic acid) hydrogel microparticles either protected or released the vitamin B₁₂ effectively depending on pH.     

Synthesis and characterization of polycation block copolymer Poly(l-lysine)-b-poly[N-(N′,N′-diisopropyl-aminoethyl)aspartamide] as potential pH responsive gene delivery system

A series of Poly(l-lysine)_m-b-poly[N-(N′,N′-diisopropylaminoethyl) aspartamide]_n copolymers, abbreviated as PLL_m-b-P[Asp(DIP)]_n were designed and synthesized via ring-opening polymerization(ROP), click chemistry, aminolysis and hydrolysis. Using ¹H NMR, FT-IR and GPC, the structures and compositions of these copolymers have been verified. Through feed ratio control, block copolymer PLL_m-b-P[Asp(DIP)]_n with different PLL and PAsp(DIP) block lengths were obtained, which can be modified to adjust the pH responsiveness and the self-assembling behaviors of the PLL_m-b-P[Asp(DIP)]_n. From the results of DLS, TEM and ¹H NMR, these block copolymers can form stable micelles with a partially hydrated PAsp(DIP) core and a PLL corona at pH 7.4. While as demonstrated by ¹H NMR and TEM, these PLL_m-b-P[Asp(DIP)]_n micelle was disassembled due to further protonation of the tertiary amine in the PAsp(DIP) block at pH 5.4. These pH responsive character of the PLL_m-b-P[Asp(DIP)]_n micelles made them as potential pH responsive gene delivery system which may co-deliver drug and DNA simultaneously.     

Synthesis,characterization, and thermotropic properties of side-chain liquid crystalline polysiloxane polymers with an oligo(ethylene oxide) unit in the side chain

A series of new alkene and octenyloxy monomers containing 4′-[oligo(ethylene oxide)] n monomethyl ether 4-biphenyl ether carboxyl benzoate [MS3BDBE_n] (n = to 3) and 1- (p-methoxydiphenyl)–(carboxyl benzoate) [oligo(ethylene oxide)]n [MS_m+2BEnDB] (m = 1, 6; n = 1 to 3) as end groups were synthesized. The molecular structure of the monomers was charaterized using nuclear magnetic resonance (NMR) spectroscopy. These monomers were grafted onto poly(methylhydrosiloxane)s (PMHS) by the platinun-catalyzed hydrosilylation process. The thermal transition temeratures and mesophase textures of the monomers and the polysiloxane polymers have been determined by diffential scanning calorimetry (DSC) and by polarized optical microscopy. The effect of changes in chemical structure on the mesophase properties, glass transition temperature, isotropic temperature, and mesophase texture of the monomers and the polysiloxane polymers is discussed. Polymers PS3BDBEn showed smectic and nematic phases which were not analogous to their precursor nematic monomers MS3BDBEn. Both monomers MS_m+2BE_nDB and their polymeric homologous PS_m+2BE_nDB did not exhibit mesophase properties. This demonstrated that the polymer effect could not stabilize the mesophase obtained from mesogenic core which contained a flexible oligo(ethylene oxide) unit interconnecting aromatic group. © 1995 John Wiley & Sons, Inc.     

Chitosan nanoparticles as particular emulsifier for preparation of novel pH-responsive Pickering emulsions and PLGA microcapsules

In this work, we describe a novel and simple method for fabricating biocompatible microcapsules. Chitosan colloidal nanoparticle-coated micrometer-sized poly(lactic-co-glycolic acid) (PLGA) microcapsules were fabricated via a combined system of “Pickering-type” emulsion route and solvent volatilization method in the absence of any molecular surfactants. Stable oil-in-water emulsions were prepared using chitosan colloidal nanoparticles as a particulate emulsifier and a dichloromethane (CH₂Cl₂) solution of PLGA as an oil phase. Moreover, this stable emulsion present a good pH-responsive characteristic. The uncross-linked chitosan nanoparticles coated PLGA microcapsules were fabricated by the evaporation of CH₂Cl₂ from the emulsion, and the cross-linked chitosan nanoparticles coated PLGA microcapsules were prepared by cross-linking with glutaraldehyde and evaporation of CH₂Cl₂. The two types of microcapsules were characterized in terms of size, morphology using scanning electronic microscope (SEM), optical microscope, and so on. These observations confirm the robust nature of these cross-linked microcapsules. Moreover, a possible mechanism for the formation of these microcapsules was proposed. The combined system of Pickering emulsion and solvent volatilization opens up a new route to fabricate a variety of microcapsules.     

Influence of Poly(L-lactic acid) Molecular Weight on the Encapsulation Efficiency of Urea in Microcapsule Using a Simple Solvent Evaporation Technique

Poly(L-lactic acid) microencapsulated urea was prepared in water-in-oil-in-water (W₁/O/W₂) system by the solvent evaporation technique. The influence of poly(L-lactic acid) molecular weight on the percent loading, encapsulation efficiency, and the microcapsule morphology was studied using poly(L-lactic acid) having different number average molecular weights (M_n). Using the higher M_n, the smoother shell with complete encapsulation microcapsules was formed. Moreover, the percent loading and encapsulation efficiency of urea also increased with the poly(L-lactic acid) molecular weight. At 80,000 g/mol of poly(L-lactic acid), the obtained microcapsule gave the highest both percent loading (32%) and encapsulation efficiency (56%). The urea control release study of the prepared microcapsules was implemented by in vitro testing. The encapsulated urea was gradually released from the microcapsules, approximately 53, 29, and 22% of poly(L-lactic acid) at 3,000, 30,000, and 80,000 g/mol, respectively, for a month. These results presented the possibility of the prepared poly(L-lactic acid) microcapsules-encapsulated urea for urea control release that could be utilized in agricultural applications.     

A novel two-dimensional network self-assembled by the narrowest ladder cations [Cu(CH3COO)(bpe)(H2O)]nn+ containing the Cu2(μ-O)2 cores and the dimeric anions [Cu2(nta)2(bpe)]2− through hydrogen-bonding interaction

A novel complex [Cu(CH₃COO)(bpe)(H₂O)]_n·n/2[Cu₂(nta)₂(bpe)] ·6nH₂O) (bpe=trans-1,2-bis(4-pyridyl)ethylene) was synthesized and characterized. The molecule structure shows that it is composed of the ladder-like double chain cations [Cu(CH₃COO)(bpe)(H₂O)]_nⁿ⁺ and the dimeric anions [Cu₂(nta)₂(bpe)]²⁻. Through bridging oxygen atom of the acetate, the Cu₂ (μ-O)₂ core is formed. The ladder-like chain cation is the narrowest ladder [3.422(3) Å]. Two-dimensional undulating network is constructed by the cations and the dimeric anions through hydrogen-bonding interactions.     

How does an oxygen atom in the side chain affect the photophysical properties of alkoxy-substituted organopolysilane homopolymers and copolymers?

Alkoxy-substituted organopolysilane homopolymer (poly[SiMe(OR)]_n) and random copolymers (poly[SiMe(OR)]_m[SiMeR′]_n were synthesized and the solvatochromism and thermochromism for their absorption and fluorescence spectra were examined. The band maxima shifted to longer wavelengths with an increase in the ratio of the alkoxy side chains; however, the influence of the solvent was very small. The thermochromic shifts are dependent on the number of alkoxy side chains. Molecular dynamics calculation showed that the conformation of the polysilanes was determined by the Coulomb interaction between the alkoxy side chains, and the conformations of the polyalkoxysilanes are similar to those of polyalkylsilanes (poly[SiRR′]_n). Molecular orbital (MO) calculations manifested that the interaction between the orbitals of the oxygen atom in the side chain and those of the silicon atom in main chain (σ conjugation system) was larger in LUMO than in HOMO, and the decrease in LUMO energy shifted the absorption maxima to longer wavelength.     

Synthesis and characterization of the biomaterial poly(lactic acid‐co‐Nε‐carbobenzoyloxy‐L‐lysine) via direct melt copolymerization

With D,L ‐lactic acid and N^ϵ‐carbobenzoyloxy‐L ‐lysine [Lys(Z)] as the starting monomer material and tin dichloride as the catalyst, the drug carrier material poly(lactic acid‐co‐N^ϵ‐carbobenzoyloxy‐L ‐lysine) was synthesized via direct melt polycondensation. The copolymer was systematically characterized with intrinsic viscosity testing, Fourier transform infrared spectroscopy, ¹H‐NMR, gel permeation chromatography, differential scanning calorimetry, and X‐ray diffraction. The influences of different feed molar ratios were examined. With increasing molar feed content of Lys(Z), the intrinsic viscosity, weight‐average molecular weight, and polydispersity index (weight‐average molecular weight/number‐average molecular weight) gradually decreased. Because of the introduction of Lys(Z) with a big aromatic ring into the copolymer, the glass‐transition temperature gradually increased with increasing feed charge of Lys(Z), and all of the copolymers were amorphous. The copolymers, with weight‐average molecular weights from 10,500 to 6900 Da, were obtained and could reach the molecular weight level of poly(lactic acid) modified by Lys(Z) via the ring‐opening polymerization of the cyclic intermediates, such as lactide and morpholine‐2,5‐dione. However, a few terminal carboxyl groups might have been deprotected during the polymerization reaction under high temperatures. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The thermal transition behavior of polyorganophosphazenes

The thermal transition behavior of poly[bis(trifluoroethoxyphosphazene)] (I) and two samples of poly[bis(p-chlorophenoxyphosphazene)] (II) have been studied as representative alkoxy- and aryloxy-substituted polyorganophosphazenes. Several of the polymers of this class are reported to exhibit two first-order transitions, denoted herein as T (1) for the transition from a crystalline to mesomorphic state and T_m for the true melt. Studies of these two polymers were undertaken to gain a further understanding of this behavior. Optical microscopy on a solution-cast film of I showed that the details of spherulitic morphology persist through T(1) = 90°C and remain undisturbed through the temperature interval up to T_m = 240°C. The study of II by x-ray diffraction reveals that two sharp lines are observed above T(1) = 165°C and that orientation is not randomized upon heating to temperatures as high as 238°C. Considerable improvement in the crystalline diffraction pattern results from the thermal treatment. A detailed examination was also made by differential scanning calorimetry (DSC) of the effects of cycling through T(1), annealing in the temperature interval between T(1) and T_m and for I, the influence of controlled crystallization from the melt. The results indicate that the organization in the mesomorphic state, as influenced by thermal history, has a profound affect on the peak position, area, and sharpness of the endotherm at T(1). For I, the apparent heat of fusion at T(1) is about ten times greater than at T_m, whereas for II, no DSC peak is observed at T_m = 365°C, suggesting that the ratio of the heats of fusion at T(1) and T_m is greater than 50. However, estimated volume changes at the two transitions are nearly equal. These results are compared with those of other polymers which exhibit an intermediate state of order and with molecular liquid crystals.     

Esterolyses of p-nitrophenyl esters catalyzed by dialkylaminopyridines attached to polyorganosiloxane

Summary The present study describes the preparation of polyorganosiloxanes containing dialkylaminopyridines in their side chains (POS-DAAPs) and the use of them as catalysts for esterolyses of p-nitrophenyl esters of CH₃(CH₂) _n COOH (n=0–5). The POS-DAAPs (4, 5) were prepared from poly[(3-chlorocarbonylpropyl)methylsiloxane] (PCCPMS, 1) and two pyridine derivatives, such as 4-[(2-hydroxyethyl)methylamino]pyridine (HEMAP, 2) and 4-[4-(2-hydroxyethyl)piperidino]pyridine (HEPP, 3). Pyridyl groups of POS-DAAPs 4 and 5 were partially quaternized with dimethylsulfate (6, 7) in order to carry out esterolysis in homogenious systems. The esterolyses were examined in methanol/tris(hydroxymethyl)-aminomethane-hydrochloric acid buffer solution (vol. ratio 2/1, pH of buffer solution: 7.5) and analyzed following Michaelis-Menten like kinetics. The second-order rate constants (k ₂/K _m) of the esterolyses catalyzed by POSs 6 and 7 were 22–38 fold values of those catalyzed by the corresponding monomolecular catalysts 2 and 3. In addition, the effects of POSs were discussed from the kinetic, thermodynamic, and activation parameters.     

Structure–property relationship of pH‐sensitive (PCL)2(PDEA‐b‐PPEGMA)2 micelles: Experiment and DPD simulation

The experiment and dissipative particle dynamics simulation were carried out on four polymers with different block ratios for the investigation of the structure–property relationship of (poly(ε‐caprolactone)₂‐[poly(2‐(diethylamino)ethyl methacrylate)‐b‐poly(poly(ethylene glycol) methyl ether methacrylate)]₂ [(PCL)₂(PDEA‐b‐PPEGMA)₂] micelles. The miktoarm star polymers assembled into spherical micelles composed of PCL core, pH‐sensitive PDEA mesosphere and poly (ethylene glycol) methyl ether methacrylate (PPEGMA) shell. When decreasing pH from 7.4 to 5.0, the hydrodynamic diameter and transmittance of (PCL)₂(PDEA‐b‐PPEGMA)₂ micelles increased along with globule‐uneven‐extended conformational transitions, owing to the protonation of tertiary amine groups of DEA at lower pH conditions. Doxorubicin (DOX) was mainly loaded in the pH‐sensitive layer, and more DOX were loaded in the core when increasing drug concentrations. The in vitro DOX release from the micelles was significantly accelerated by decreasing pH from 7.4 to 5.0. The results demonstrated that the pH‐sensitive micelles could be used as an efficient carrier for hydrophobic anticancer drugs, achieving controlled and sustained drug release. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3634–3646, 2014     

Structural diversity of chlorido methoxido- and ethoxido-oxidovanadium(V) complexes: Two-dimensional network,dimer, and unusual syn-oriented V=O functionality

The syntheses and structural characterization of methoxido- and ethoxido-vanadium complexes [VOCl₂(OMe)(HOMe)₂] (1), [VOCl(OMe)₂]₂ (2), and [{VOCl(OEt)₂}₂(THF)] (3) are described. The effects of the reactant ratio, starting materials, and reaction media on the formation of the alkoxido oxidovanadium and their molecular structures are reported. Complex 1 was prepared by reaction of VOCl₃ with three equiv of MeOH in pentane. In the solid state, each molecule of 1 is linked with four symmetry related molecules through four O–H···Cl interactions resulting in the formation of a 2D infinite network. Reaction of VOCl₃ with 2 equiv of NaOMe in pentane yields the dimeric complex 2, which features a pair of methoxido bridges in the molecular structure. In THF, reaction of VOCl₃ with 2 equiv of NaOEt results in a very thermolabile [{VOCl(OEt)₂}₂(THF)] (3), which adopts a butterfly conformation in the molecular structure and features an interesting alkoxido oxidovandium with syn-orientated V=O functionality.     

Enhancement of orientation of rigid polymer blocks by incorporating rod–coil block copolymer chains into metal–organic frameworks

Incorporation of polymer chains into metal–organic frameworks (MOFs) is a simple yet efficient method for improving the orientation of the polymer chains. However, due to their rigidity and high molecular weight, many rigid polymer chains are either not easily loaded into MOFs, or not easily aligned within the MOF channels. In this paper, we propose a strategy for enhancing the orientation of rigid blocks by incorporating rod–coil block copolymer chains into MOFs. In this strategy, on the one hand, the rigid blocks have a low molecular weight, so that the steric hindrance effect from the MOF channels could align the rigid blocks more efficiently. On the other hand, because the covalent bonds between the repeat units of the flexible blocks can rotate relatively easily, the steric hindrance effect from the flexible blocks can further help the rigid blocks to be oriented within the MOF channels. In confirmatory simulations, two all‐atom MOF models, [Zn₂(BDC)₂(TED)]_n and [Zn₂(BPDC)₂(TED)]_n (TED = triethylenediamine, BDC = 1,4‐benzenedicarboxylate, BPDC = 4,4′‐biphenyldicarboxylate), are established. With these MOF models, molecular dynamics simulations are performed for the rigid poly(phenylene vinylene) (PPV) chain and the rod–coil block copolymer PPV‐block‐polystyrene (PSt). Further, their respective degrees of orientation (DoOs) are calculated. Within [Zn₂(BDC)₂(TED)]_n and [Zn₂(BPDC)₂(TED)]_n, the DoOs of the rigid PPV blocks of PPV‐block‐PSt are 0.968 and 0.902, respectively, while the DoOs of the rigid PPV chains are 0.865 and 0.711, respectively. These calculation results prove the feasibility of our proposed strategy. © 2019 Society of Chemical Industry     

The role of reaction medium on the coordination environment of terbium in complexes with 4-acylpyrazol-5-ones

[Tb(Q)₃(H₂O)] and [Tb(Q)₃(H₂O)(EtOH)] derivatives of novel 1-phenyl-3-methyl-4-R-pyrazol-5-one (HQ=HQ^CP: R=cyclopentylcarbonyl, HQ^ETCP: R=cyclopentylpropionyl) have been prepared and shown to be seven- and eight-coordinate, respectively, by IR, X-ray and elemental analyses. The role of the reaction medium on the coordination number of Tb is discussed.     

pH-responsive PEGylated nanogel containing platinum nanoparticles: Application to on–off regulation of catalytic activity for reactive oxygen species

Synthesis of pH-responsive PEGylated nanogels platinum nanoparticles (PtNPs: <2 nm) was successfully carried out through the reduction of K₂PtCl₆ within the PEGylated nanogels constructed from cross-linked poly[2-(N,N-diethylamino)ethyl methacrylate] (PDEAMA) core and tethered PEG chains. The resulting PEGylated nanogels containing PtNPs showed significant catalytic activity for reactive oxygen species (ROS) in response to skin-environmental pH (acid), whereas the almost no catalytic activity for ROS was observed at physiological pH due to the volume phase transition of the PDEAMA gel core. Thus, pH-responsive and PEGylated nanogel containing PtNPs can be utilized to the skin-specific ROS-scavengers for the skin aging.     

Construction of three new mixed-ligand Zn(II) coordination polymers based on nitrogen-containing heterotopic ligands and carboxylate co-ligands

Reactions of Zn(II) salts, presynthesized 5-(4-(1H-imidazol-1-yl)phenyl)-1H-tetrazolate (HIPT) and various carboxylate ligands result to three new coordination polymers (CPs), namely, [Zn₂[(IPT)₂(ox)]}_n (H₂ox = oxalic acid, 1), [Zn₂(IPT)₂(mNBDC)]_n (H₂mNBDC = 5-nitroisophthalic acid, 2), and [Zn₂(IPT)(CA)(H₂O)]_n (H₃CA = citric acid, 3). Compound 1 can be seen as constructed from 2D [Zn(IPT)]_n layers with (6,3) topology and pillared by ox^2 −. It is a 3D (3,4)-connected framework with InS topology. Compound 2 has 2D bilayer structure based on 2D [Zn(IPT)]_n single layer and mNBDC^2 − linkers. Compound 3 is a 3D pillar-layer framework built by Zn–CA bilayers and IPT⁻ pillars. The results showed that the coordination modes, configurations of IPT⁻, and the structure of carboxylate co-ligands have great influence on the structures of the final network. The choice of carboxylate can decide the result of CPs in Zn–IPT chains/net subunits plus carboxyl linkers or Zn–carboxylate chains/net subunits plus IPT⁻ linkers. The thermal stabilities and luminescent properties of selected compounds have also been studied.     

A New 4-Connected Co(II) Coordination Framework With an Uncommon Two-Fold Interpenetrating Net: Synthesis, Structure and Luminescence Property

The coordination polymer [Co(pbc)₂(H₂O)]_n(Hpbc = 3-Pyrid-4-ylbenzoic acid) was prepared by hydrothermal synthesis and characterized by single-crystal X-ray diffraction, FTIR spectra and element analysis. X-ray diffraction analysis reveals that the pbc⁻ ligands act as diconnectors to link two Co(II) centers and adopt a two coordination mode: μ ₂-N, O and μ ₂-N, O, O to form infinite wavy cobalt-carboxylate chains along the bc plane. Furthermore, compound, [Co(pbc)₂(H₂O)]_n, shows intense photoluminescence at room temperature.     

Synthesis of Some 4-Aryl Substituted Poly(alkyl/arylphosphazenes)

A series of 4-aryl substituted poly(alkyl/arylphosphazenes), [N=P(Me)(p-C₆H₄–X]_n (X = Br, Cl, OMe, CF₃), were prepared via the thermal condensation polymerization of the corresponding N-silylphosphoranimines, Me₃SiN=P(Me)(p-C₆H₄–X)–OR (R = CH₂CF₃, Ph). The new polymers were obtained in high yields and characterized by NMR spectroscopy and molecular weight measurements. Treatment of some of the same Si–N=P precursors with trifluoroethanol afforded the non-geminally substituted cyclic trimers, [N=P(Me)(p-C₆H₄–X]₃ (X = OMe, CF₃) as mixtures of cis and trans isomers. The pure cis isomer of the methoxy derivative was isolated and structurally characterized by X-ray diffraction. This paper is dedicated to Professor Chris Allen in honor of his outstanding contributions to the fields of inorganic polymer and main group element chemistry.     

Ultralow Tribological Properties of Polymer Composites Containing [BMIm]PF6‐Loaded Multilayer Wall Microcapsule

Multilayer wall microcapsules efficiently loaded with a lubricant (ionic liquid [BMIm]PF₆) are successfully synthesized via a combination of interfacial and in situ polymerization reactions based on lignin nanoparticle–stabilized Pickering emulsion templates. The resulting microcapsules are spherical in shape, with an ideal structure of a rough outer surface and a smooth inner surface. The mean diameter and wall thickness of the resultant microcapsules are 52 ± 18 µm and 3–6 µm. The core fraction is ≈71.29 wt%. Compared with the pure epoxy resin, the friction coefficient of self‐lubricating composites decreases by 83.6% (from 0.55 to 0.09) and the wear rate decreases by 218 times (from 76.8 × 10^?14 to 0.352 × 10^?14 m³ N^?1 m^?1) by incorporating 20 wt% of the resultant microcapsules into the epoxy resin. It is demonstrated that [BMIm]PF₆, a more efficient lubricant, release from the microcapsules during the friction process produced a boundary lubricating film. The bipolar property of [BMIm]PF₆ makes the lubricating film firmer, which can efficiently prevent direct contact between the resin matrix and counterface. Furthermore, the rough poly(urea‐formaldehyde) outer surface of multilayer microcapsules brings in an improved interface property between the microcapsules and resin matrix.     

A facile strategy to fabricate carboxyl-rich carbon spheres with copper-based MOFs through coordination bond

A new composite (CCSs/MOFs) of carboxyl-rich carbon spheres (CCSs) and copper-based metal–organic frameworks (MOFs) was for the first time prepared. The CCSs/MOFs composite was synthesized by the coordinated growth of high surface area and porous MOFs, [Cu₃(BTC)₂(H₂O)]_n (HKUST-1), on the surface of the functionalized CCSs obtained through a one-step hydrothermal carbonization of glucose with acrylic acid at 180 °C for 24 h. The resulting composites showed a core/shell structure with a tunable diameter arranging from 0.6 to 3.0 μm, and possessed high specific surface area of 495 m²/g and nanoporous structures derived from MOFs. Further, the catalytic oxidation of benzylic alcohol to benzaldehyde as its application was studied.