Oxidation of Hydroquinone By (N-Vinylpyrrolidone)-(4-Vinylpyridine) Block and Graft Copolymers

ABSTRACT

A-B Type block copolymer of N-vinylpyrrolidone (NVP) and 4-vinylpyridine (VPy) [poly(NVP-b-VPy) and graft copolymers of VPy onto copolymers of NVP with 4-vinylbenzyl N,N-diethyldithiocarbamate (VBDC) [poly(NVP-g-VPy) were synthesized by the iniferter method. the compatibility between NVP and VPy units in the copolymers was evaluated from the glass transition temperature of these copolymers. Hydroquinone was then oxidized by the synthesized NVP-VPy copolymers-Cu(II) complex catalysts. the influence of the distribution of each monomer unit in copolymers on the catalytic activity was studied by comparing the activity of these copolymers. the catalytic activity of these copolymers increased in the order: NVP-VPy blend polymer, poly(NVP-b-VPy), poly(NVP-g-VPy), random copolymer [poly(NVP-ran-VPy)]. This order parallels the compatibility between NVP units and VPy units in these copolymers.     

Amphiphilic Graft Copolymers as Phase-Transfer Catalysts in a Solid-Liquid System

Abstract

Amphiphilic graft copolymers consisting of a hydrophobic backbone and poly(oxyethylene) (PEO) side chains were employed as solidliquid phase-transfer catalysts (PTC) in the substitution of octylbromide by solid potassium phenoxide in toluene. A wide variety of structures were synthesized via ester substitution of poly(phthalimidoacrylate) (PPIA) or poly(phthalimidoacrylate-co-styrene) [poly(PIA-co-St)] with amino-functionalized methoxy-PEO (MPEO-NH₂). The phase-transfer catalytic activity (PTA) of these soluble graft copolymers was studied as a function of the structure of the backbone, the length of the side chains, and the graft density. The graft copolymers of a high degree of grafting showed PTA higher than that of parent PEOs. GPC was used to study the behavior of the graft copolymers in toluene at 90°C. It is believed that the phase-transfer reaction is accelerated in the PEO microphase.     

Free-Radical Synthesis of Block Copolymers via Dixanthogen-Linked Polymer Sequences

Abstract

Due to high chain transfer and the subsequent terminator properties of the dixanthogen moiety, (AB)_n multiblock copolymers of poly(oxyethylene-block-methyl methacrylate) and ABA triblock copolymers of poly(methyl methacrylate-block-2-ethylhexyl acrylate) could be synthesized from dixanthogen-linked poly(oxyethylene) and poly(methyl methacrylate) pre-polymer sequences, respectively, using free-radical chemistry. A simple and efficient method was developed for the synthesis of dixanthogen-linked polymers: Hydroxyl-functionalized pre-polymers were reduced using NaH to form alkoxide; CS₂ was then added to the alkoxide to form xanthate; and finally the xanthate was oxidized either in an aqueous or organic medium to form the dixanthogen. The synthesis techniques provided in this paper are general and thus, in principle, can be applied to many other block copolymer systems.     

利用超分子接枝聚合物体系制备具有pH响应能力的高分子囊泡及其在药物控制释放方面的应用

利用自由基聚合的链转移反应,制备了以羧基为端基的聚(N-异丙基丙烯酰胺)(PNIPAM-COOH),然后以该聚合物作为亲水的侧链,利用其羧端基和聚(4-乙烯基吡啶)(PVPy)疏水主链上的吡啶基团间的相互作用,在共溶剂DMF中形成超分子两亲接枝聚合物体系,在上述体系中逐滴加入水可以使其通过自组装形成高分子囊泡.通过控制PVPy与PNIPAM-COOH的质量比在1～3之间,可以控制囊泡尺寸在130～330nm之间.由于囊泡中含有吡啶基团,因而该囊泡具有pH敏感性.以日落黄为药物模型,以这些pH敏感性囊泡作为药物载体,通过调节环境的pH值可以实现对药物的控制释放.     

Novel Polyurethane Multiblock Copolymers and Their Zwitterionomers Using a Polyurethane Macroiniferter

Abstract

Polyurethane-poly(4-vinylpyridine) multiblock copolymers have been prepared by the decomposition of a tetraphenylethane-based polyurethane macroiniferter in the presence of 4-vinylpyridine. The increase in the molecular weight and conversion with an increase in polymerization time proves the “living” radical mechanism. The polyurethane-poly(4-vinylpyridine) multiblock copolymers so obtained were converted into their zwitterionomers by treating with γ-propane sultone. Both block copolymers and their zwitterionomers have been characterized using spectral and thermal techniques.     

Acid/base properties of poly(4-vinylpyridine) anchored within microporous membranes

Membranes consisting of poly(4-vinylpyridine) anchored within the pores of microporous polypropylene and polyethylene membranes exhibit a very large, fully reversible change in permeability over a very narrow pH range (pH valve). A detailed examination of the acid/base properties of the incorporated poly(4-vinylpyridine) has been undertaken in order to understand the factors affecting the position (pH) at which this valve operates. It was shown that the position and magnitude of the valve is the same when either HCl, H₃PO₄, or CH₃COOH are used to adjust the acidity of the feed solution, indicating that pH of the aqueous phase is the major determining factor controlling the valve operation with these acids. However, the valve behavior of the membrane with H₂SO₄ was found to be completely different than with the other acids in that the valve both closed at a substantially higher pH than with the other acids and then fully re-opened when the pH was decreased below 3. Potentiometric titrations of membranes containing poly(4-vinylpyridine) and control experiments involving solutions/suspensions of the homopolymer in water were undertaken. It was found that there are substantial differences in the protonation of poly(4-vinylpyridine) both in terms of its environment (membrane bound or in solution) as well as with the acid used. The differences in the pK observed between H₂SO₄ and the other acids are discussed in terms of conformational changes of poly(4-vinylpyridine) which are induced by both protonation and the counter-ion (anion) present. The results of potentiometric titrations parallel the valve behavior of the membranes. The conformational changes underlying the pH valve effects in different acids were visualized by atomic force microscopy and followed by thickness changes in the membranes.     

Design of water-soluble block copolymers containing poly(4-vinylpyridine) by atom transfer radical polymerization

The preparation of block copolymers consisting of poly(4-vinylpyridine) (P4VP) by atom transfer radical polymerization (ATRP) was investigated. The goal was to synthesize water-soluble block copolymers with poly(ethylene oxide) (PEO) as first block, a water-soluble polymer at any pH. First, a PEO macroinitiator was prepared for the ATRP block copolymerization of 4-vinylpyridine. In the second stage, the kinetic behaviour of this block copolymerization was investigated for two different types of PEO-macroinitiators and catalyst systems, based on CuCl or CuCl₂/Cu(0), with tris[2-(dimethylamino)ethyl]amine (Me₆-TREN) as the ligand. Various combinations of initiator and catalyst led to a controlled block copolymerization with optimized results obtained for chlorinated poly(ethylene glycol) monomethyl ether as macroinitiator, together with CuCl₂/Cu(0)/Me₆-TREN as catalyst system. With the latter system, narrow polydispersities (1.25) could be reached for PEO-P4VP block copolymers.     

Synthesis and Characterizations of Copolymers Containing Both Phosphatidylcholine Analogues and Poly(Ethylene Glycol) in the Side Chains

Abstract

New phospholipid analogous polymers were prepared by radical copolymerizations of 2-(methacryloyloxy)ethyl-2-(trimethylammonio)-ethyl phosphate and poly(ethylene glycol)monomethylether methacrylates (PEGMM) at room temperature, using (NH₄)₂S₂O₈ as the initiator and pure water as the solvent. The copolymers obtained were characterized based on their IR, ¹H-, and ¹³C-NMR spectral data and melting point measurements. The molecular weights of these copolymers decrease as the length of the PEGMM side chain increases. These new polymers, which contain phosphatidylcholine analogous groups in their side chains, show viscosity properties similar to typical polyelectrolytes.     

Synthesis and Characterization of Triphenylphosphine Oxide-Containing Poly(Aryl Imide)-Poly(Dimethyl Siloxane) Randomly Segmented Copolymers

Abstract

Poly(aryl imide)-poly(dimethyl siloxane) randomly segmented copolymers were synthesized by essentially a one-step solution imidization process in a solvent system consisting of predominately o-dichlorobenzene with a small amount of n-methylpyrolidone. This solvent combination was selected because of its ability to afford homogeneous solutions throughout the polymerization process. This enabled copolymers of any desired poly(dimethyl siloxane) composition to be prepared. A hydrolytically stable triphenylphosphine oxide containing diamine, bis(3-amino-phenoxy-4′-phenyl)phenylphosphine oxide, was utilized as a chain extender and together with oxydiphthalic anhydride formed the hard segment in these copolymers. The soft segment was formed from α,ω-aminopropyl poly(dimethyl siloxane) oligomers of controlled molecular weight. The presence of phosphorus and silicon contributes several unique properties to the system, including enhanced solubility, thermal stability, and flame resistance. High molecular weight copolymers containing up to 60% (w/w) of the poly(dimethyl siloxane) segments were successfully prepared using this method. Gel permeation chromatography analysis, based on a universal calibration curve in CHCl₃, was performed to determine the molecular weights and distribution. These copolymers with 40-60% (w/w) poly(dimethyl siloxane) exhibited upper T_g values ranging from 130 to 180°C and showed substantial char yields at 750°C in air, which increased with siloxane content. Dynamic mechanical analysis confirmed the anticipated microphase behavior by the presence of two separate glass-transition regions. Both small angle x-ray scattering and transmission electron microscopy measurements determined on well-characterized transparent cast films were used to better demonstrate the multiphase nature of these copolymers.     

Synthesis of poly(4-vinyl pyridine-b-methyl methacrylate) by MAMA-SG1 initiated sequential polymerization and formation of metal loaded block copolymer inverse micelles

Well-defined poly(4-vinylpyridine) (P4VP) was synthesised by nitroxide-mediated radical polymerization using the BlocBuilder MAMA-SG1. The controlled character of the polymerization was confirmed by kinetic measurements and linear increase of the molar mass with monomer conversion. Poly(4-vinylpyridine) terminated with SG1 was then used as macroinitiator and chain extended to form poly(4-vinylpyridine-b-methyl methacrylate) and poly(4-vinylpyridine-b-(methyl methacrylate-co-styrene)) block copolymers. These block copolymers spontaneously organized into spherical inverse micelles in THF with critical micelle concentrations of 0.1 mg/mL for poly(4VP₁₉₀-b-MMA₉₁) and 0.01 mg/mL for poly(4VP₁₉₀-b-(MMA₅₇-co-S₁₈)) and sizes of 70 and 130 nm (DLS), respectively. The inverse micelles were loaded with copper(II)acetate leading to a slight increase in micelle size. The uniform structure of the inverse micelles was confirmed by FeSEM images, while the presence of copper in the micelle core was established by energy-dispersive X-ray spectroscopy (EDX) and FTIR spectroscopy.     

Porous,polyelectrolyte-filled membranes: Effect of cross-linking on flux and separation

A new type of membrane composed of a microfiltration substrate and a pore-filling polyelectrolyte has been produced by UV-induced grafting of 4-vinylpyridine (4VP) with varying amounts of divinylbenzene (DVB) onto polypropylene microfiltration membranes. Using the same irradiation conditions, it has been found that graft yield increases substantially in the presence of DVB. The increase in graft yield was shown to be accompanied by a substantial increase in the thickness of the grafted membranes and a small but significant decrease in water content. The composite membranes have very high charge densities and good mechanical properties.The membranes with various amounts of DVB were quaternized (methylated) and examined for reverse osmosis of various salts. In addition to an expected drop in flux due to the increased thickness and decreased water content, there was significantly different salt rejection for membranes with cross-linking. While, for example, there is practically no difference in rejection of NaCl by a membrane with 0.55% DVB and one having no cross-linker, the Na₂SO₄ rejection by the cross-linked membrane is, on average, twice as high as that by the non-cross-linked one. Large differences between the cross-linked and non-cross-linked membranes were found in the ratios of pure water to NaCl permeate fluxes of the membranes at various pressures. The results are discussed in terms of the physicochemical nature of the membranes and conformational changes of the pore-grafted poly(4-vinylpyridine).     

Influence of Solvent Polarity on Elution Volume in the Case of Polar Polymers

Abstract

The influence of solvent polarity on elution volume has been studied in the case of polar polymers such as homopoly-2-vinylpyridine and polystyrene-poly-2-vinylpyridine block or graft copolymers eluted on crosslinked polystyrene gels in tetrahydrofuran or dimethylformamide medium.     

pH-Responsive Films of Electrostatically Adsorbed Arborescent Copolymers

The adsorption of charged dendrigraft (arborescent) copolymers of different generations (G1, G2) and side chain molecular weights (M_n ≈ 5000 or 30,000) on silica surfaces in water, was monitored by the quartz crystal microbalance dissipation (QCM-D) technique. The topology of the adsorbed copolymers on mica was also investigated by AFM measurements. The PS-P2VP [polystyrene-graft-poly(2-vinylpyridine)] copolymers readily interact with a silica or mica surface and form a thin layer in acidic water (pH 2) due to the positively charged P2VP shell branches. The adsorbed arborescent PS-P2VP films expanded and collapsed reversibly in water upon cycling between low and high pH values, respectively. As the generation number increased, the density of copolymer molecules adsorbed onto the surface decreased due to stronger intermolecular electrostatic repulsions. The adsorption density also decreased significantly for copolymers with longer P2VP chains due to their more expanded conformation on the surface.     

Self-Assembly of Rod-Coil Block Copolymers for Photovoltaic Applications

Summary: Two different approaches to obtain electron donor-acceptor interfaces via self-assembly of block copolymer systems are discussed, where the donor domains are formed by a π-conjugated rod-like polymer and the acceptor domains result from a coiled polymer modified by C₆₀ fullerenes. In the first strategy, C₆₀ is chemically grafted onto the coil polymer, typically a statistical copolymer of styrene and chloromethyl styrene. This has as major effect the increase in molecular weight and volume fraction of the coil block, which can markedly perturb the self-assembled block copolymer final morphologies and eventually suppress any microseparated nanostructure in favour of fully isotropic homogeneous phases. We discuss how the presence of free homopolymer rods in the system can help recovering a microphase separated morphology suitable for photovoltaic applications. In the second approach we discuss the poly(diethylhexyl-p-phenylenevinylene-b-4-vinylpyridine) (PPV-P4VP) rod-coil block copolymer system and we argue how supramolecular interactions among P4VP and free C₆₀ can be exploited to blend rod-coil block copolymers and C₆₀ preserving the original lamellar phase.     

Linking reactions of living polymers with bromomethylbenzene derivatives: Synthesis and characterization of star homopolymers and graft copolymers with polyelectrolyte branches

Anionic polymerization techniques utilizing 1,2,4,5-tetra(bromomethyl)- benzene as the linking agent were employed for the synthesis of four-arm star polymers with poly(tert-butyl methacrylate) (PtBuMA), poly(methyl methacrylate), poly(tert-butylacrylate) (PtBuA), or poly(2-vinylpyridine) (P2VP) branches. This work was extended through the “grafting onto” method, in combination with anionic polymerization techniques, to synthesize graft copolymers consisting of polystyrene backbones and PtBuA, PtBuMA, or P2VP branches. Postpolymerization reactions were performed to produce graft copolymers with polyelectrolyte branches. Crosslinking reactions were observed in some of the graft materials several months after their preparation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4337–4350, 1999     

Improving the Structural Control of Graft Copolymers. Copolymerization of Poly(dimethylsiloxane) Macromonomer with Methyl Methacrylate Using RAFT Polymerization

Reversible addition‐fragmentation chain transfer was applied to the copolymerization of methyl methacrylate and a methacrylate‐terminated poly‐(dimethylsiloxane) macromonomer (PDMS‐MA). The relative reactivity of PDMS‐MA (1/r_MMA) was higher than in the conventional radical copolymerization and similar to that in the atom transfer radical copolymerization. The obtained graft copolymers had much lower polydispersities than those obtained in the conventional radical systems.     

Precision synthesis of graft copolymers via living cationic polymerization of p‐acetoxystyrene followed by friedel–crafts‐type termination reaction

This study describes a novel precision synthesis strategy for graft copolymers using Friedel–Crafts‐type termination reaction between a cationically prepared poly(styrene derivative) and the naphthyl side groups from a poly(vinyl ether) main chain. The pendant alkoxynaphthyl groups on the poly(vinyl ether) efficiently terminated the living cationic polymerization of p‐acetoxystyrene (AcOSt) with SnCl₄ in the presence of ethyl acetate as an added base. This research provides the first example of a well‐defined graft copolymer prepared using this method. The resulting polymer contained 40 poly‐(AcOSt) branches, as calculated from the M_w determined via gel permeation chromatography–MALS analysis, which was in good agreement with the estimated number of branches obtained from ¹H NMR analysis. The acetoxy groups in the grafted poly(AcOSt) chains were easily converted into phenolic hydroxy groups under basic conditions. The as‐obtained graft copolymer with poly(p‐hydroxystyrene) side chains exhibited a pH‐sensitive phase separation in water. The synthetic method for preparing the graft copolymers was also effective in the living cationic polymerizations of other styrene derivatives. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4675–4683     

Precise synthesis of thermo-responsive and water-soluble star-branched polymers and star block copolymers by living anionic polymerization

A series of thermo-responsive and water-soluble 4- and 8-arm star-branched poly(2-(2′-methoxyethoxy)ethyl methacrylate) (poly(1)) with well-defined structures were synthesized by living anionic polymerization of 1, followed by a linking reaction with a core compound substituted with either four or eight benzyl bromide moieties. Furthermore, two kinds of sequentially different 4-arm star block copolymers composed of poly(1)-block-poly ((2,2-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate) (poly(4)) were also synthesized by the same linking reaction of the corresponding AB or BA diblock copolymer anion with a core compound substituted with four benzyl bromide moieties. Thus, both well-defined 4-arm (AB)₄ and (BA)₄ star-block copolymers, whose A and B are poly(1) and poly(4) segments, were successfully synthesized. These star-block copolymers were quantitatively converted to the corresponding 4-arm (AC)₄ and (CA)₄ star-block copolymers with the same compositions by hydrolytic acetal cleavage of the poly(4) segment to poly(2,3-dihydroxypropyl methacrylate) (C segment). Poly(1) segments have LCST values and, on the other hand, both water-insoluble poly(4)s and water-soluble poly(2,3-dihydroxypropyl methacrylate)s are non-thermo-responsive segments. The thermo-responsive behavior of the resulting 4- and 8-arm star-branched poly(1) as well as the 4-arm (AB)₄, (BA)₄, (AC)₄, and (CA)₄ star-branched block copolymers has been extensively studied in terms of molecular weight, arm number, composition, and block sequence. As expected, such variables were observed to affect their LCST values. Interestingly, the thermo-responsive behavior of the 4-arm (AC)₄ and (CA)₄ stars was different from that of the block copolymers used as arm segments.     

Novel Amphiphilic Block Copolymers for the Formation of Stimuli-Responsive Non-Lamellar Lipid Nanoparticles

Non-lamellar lyotropic liquid crystalline (LLC) lipid nanoparticles contain internal multidimensional nanostructures such as the inverse bicontinuous cubic and the inverse hexagonal mesophases, which can respond to external stimuli and have the potential of controlling drug release. To date, the internal LLC mesophase responsiveness of these lipid nanoparticles is largely achieved by adding ionizable small molecules to the parent lipid such as monoolein (MO), the mixture of which is then dispersed into nanoparticle suspensions by commercially available poly(ethylene oxide)–poly(propylene oxide) block copolymers. In this study, the Reversible Addition-Fragmentation chain Transfer (RAFT) technique was used to synthesize a series of novel amphiphilic block copolymers (ABCs) containing a hydrophilic poly(ethylene glycol) (PEG) block, a hydrophobic block and one or two responsive blocks, i.e., poly(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl acrylate) (PTBA) and/or poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA). High throughput small angle X-ray scattering studies demonstrated that the synthesized ABCs could simultaneously stabilize a range of LLC MO nanoparticles (vesicles, cubosomes, hexosomes, inverse micelles) and provide internal particle nanostructure responsiveness to changes of hydrogen peroxide (H₂O₂) concentrations, pH and temperature. It was found that the novel functional ABCs can substitute for the commercial polymer stabilizer and the ionizable additive in the formation of next generation non-lamellar lipid nanoparticles. These novel formulations have the potential to control drug release in the tumor microenvironment with endogenous H₂O₂ and acidic pH conditions.     

Preparation and properties of alkylated poly(styrene-graft-ethylene oxide)

Poly(styrene-graft-ethylene oxide), having alkyl chains (C₁₂ or C₁₈) on the polystyrene main chain or on the poly(ethylene oxide) (PEO) side chains, were synthesized. The main chain was alkylated by first ionizing amide groups in a styrene/acrylamide copolymer with tert-butoxide, and then using the amide anions as sites for reactions with 1-bromoalkanes. An excess of amide anions was used in the reaction, and the remaining anions were subsequently utilized as initiator sites for the anionic polymerization of ethylene oxide (EO). Synthesis of poly(styrene-graft-ethylene oxide) with alkylated side chains was accomplished by polymerization of EO onto the ionized styrene/acrylamide copolymer, followed by an alkylation of the terminal alkoxide anions with 1-bromoalkanes. The alkylated graft copolymers were structurally characterized by using elemental analysis, ¹H NMR, GPC, and IR spectroscopy. DSC analysis showed that only graft copolymers with PEO contents exceeding about 50 wt % and side chain crystallinities comparable to those of homo-PEO. Main chain alkylated graft copolymers generally had higher crystalinities, as compared to nonalkylated and side chain alkylated samples. The graft copolymers absorbed water corresponding to one water molecule per EO unit at low PEO contents. The water absorption increased progressively at PEO contents above 30 wt % for main chain alkylated samples and above 50 wt % for non-alkylated samples. © 1995 John Wiley & Sons, Inc.