Molecular-hydrodynamic study of poly(<Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="Italic">N</Emphasis>-vinylacetamide) macromolecules

High-velocity sedimentation, translational isothermal diffusion, and viscometry in H₂O and DMF are used to investigate the samples and fractions of poly(N-methyl-N-vinylacetamide) synthesized by free-radical polymerization and fractionated in a chloroform-diethyl ether system. Molecular masses M and the Mark-Kuhn-Houwink-Sakurada relations are obtained for the fractions in the molecular mass range M × 10⁻³ = 3.5−540.0. The negative temperature coefficient of intrinsic viscosity is revealed for both solvents. The length of the Kuhn statistical segment and the hydrodynamic diameter of poly(N-methyl-N-vinylacetamide) macromolecules are estimated; the hydrodynamic volumes occupied by water-soluble poly(N-methyl-N-vinylacetamide), poly(1-vinyl-2-pyrrolidone), poly(vinylformamide), and pullulan molecules are compared.     

Synthesis of glucose-substituted poly(<Emphasis Type="Italic">p</Emphasis>-phenylene)s with twisted main-chain in one direction due to induced axial chirality

Summary The peracetylated and free glucose-substituted poly(p-phenylene)s were synthesized by the coupling polymerization of a dibromobenzene monomer using Ni complex and the subsequent deacetylation by hydrazine monohydrate. The polymerization was carried out using bis(1,5-cyclooctadiene)nickel(0) (Ni(COD)₂) as a coupling agent with 2,2’-bipyridyl (bpy) and 1,5-cyclooctadiene (COD) in a mixed solvent of DMF and toluene. The structure of the product was confirmed by ¹H and ¹³C NMR measurements to be the poly(p-phenylene) having peracetylated glucose residues. The M_n values were estimated by GPC analysis with DMF as eluent to be 7300–9800. The fluorescence analysis of the polymer was carried out in comparison with that of the dimeric model compound. The CD spectrum of the polymer indicated that the main-chain was twisted and immobilized in one direction due to the chirality and bulkily of the peracetylated glucose residues. The deacetylation using hydrazine monohydrate completely took place to give the free glucose-substituted poly(p-phenylene).     

Dispersion polymerization of <Emphasis Type="Italic">N</Emphasis>-vinyl caprolactam in supercritical carbon dioxide

Dispersion polymerization of N-vinyl caprolactam (NVCL) was carried out in supercritical carbon dioxide (scCO₂) using three surfactants. The polymerization was performed in the presence of fluorine-based poly(heptadecafluorodecyl acrylate) (PHDFDA), poly(heptadecafluorodecyl methacrylate) (PHDFDMA) or siloxane-based PDMS-g-pyrrolidonecarboxylic acid (Monasil PCA) as a surfactant. FE-SEM and image analyzer were used to characterize particle morphology, size, and size distribution. When fluorine-based surfactants were used, spherical PVCL particles were obtained. Using Monasil PCA resulted in agglomerated and irregular polymer particles. The effect of concentration of surfactants, initiators, and monomer, and reaction pressure on the particle morphology, average particle size and particle size distribution (PSD) was also investigated with fluorine-based surfactant, PHDFDA or PHDFDMA.     

Synthesis of poly(<Emphasis Type="Italic">p</Emphasis>-phenyleneethynylene)s bearing oligo-ethylene glycols and their gas permeation properties

1,4-Diiodobenzenes bearing oligo-ethylene glycols [IRC₆H₂IR, R = OCH₂CH₂OCH₃ (1a), O(CH₂CH₂O)₂CH₃ (1b), O(CH₂CH₂O)₃CH₃ (1c)] were polymerized with 1,4-diethynylbenzene in the presence of Pd/Cu catalyst to afford poly(p-phenyleneethynylene)s bearing oligo-ethylene glycols (2a–c), respectively. Polymer 2a was insoluble in any solvents, but the other polymers (2b, 2c) were soluble in CHCl₃. The weight-average molecular weights of 2b and 2c were 5.4 × 10⁴ and 9.6 × 10⁴, respectively, and they gave free-standing membranes by solution-casting method. The densities of membranes of 2b and 2c were 1.26 and 1.22 g/cm³, respectively, and their carbon dioxide permeability coefficients were 12.9 and 13.5 barrers, respectively. The CO₂/N₂ separation factor of membrane of 2b was as large as 33.7. Membrane of 3b, which contains triethylene glycols, exhibited higher CO₂ permselectivity, and the CO₂/N₂ separation factor was 50.0.     

From 1-<Emphasis Type="SmallCaps">d</Emphasis> to 3-<Emphasis Type="SmallCaps">d</Emphasis> Supramolecular Structures Derived from Diphenic Acid and Auxiliary Ligands

Four novel compounds [Co(Hdpa) ₂(4,4′-bipy)₂]_n (1), {[Ni(dpa)(2,2′-bipy)(H₂O)](H₂O)}_n, (2), [Ni(dpa)(im)₃]_n (3) and [Zn(dpa)(im)]_n (4) [H₂dpa = 2,4′-diphenyl-dicarboxylic acid, 4,4′-bipy = 4,4′-bipyridine, 2,2′-bipy = 2,2′-bipyridine and im = imidazole] were synthesized and characterized by elemental analysis, IR and single-crystal X-ray diffraction. X-ray crystallography shows that the 2,4′-diphenic acid exhibits three coordination modes to link the metal ions: μ ₁ −η¹: η¹/μ ₀ −η⁰: η⁰, μ ₁−η ¹: η ⁰/μ ₂−η ¹: η ¹ and μ ₁−η ¹: η ⁰/μ ₁−η ¹: η ⁰. Compound 1 has a 1D supramolecular structure. Compounds 2 and 3 are 3D supramolecular structures. Compound 4 is a 2D supramolecular structure. All the compounds, 1–4, are self-assembled to form supramolecular structures through hydrogen bonding interactions.     

Cmc of PMMA-<Emphasis Type="Italic">block</Emphasis>-PDMAEMA measured by NPN fluorescence

Relationships able to predict the behavior of polymers based on their chemical structure are necessary for the rational synthesis of materials with desired properties. The state-of-art of polymer chemistry allows one to synthesize, using techniques such as RAFT, polymers with tailored chemical structures to study that kind of relationships. In this study, RAFT was used to synthesize copolymers—poly(methyl methacrylate)-block-poly[(2-dimethylamino)ethyl methacrylate]—that form aggregates in water at neutral and acidic pH’s. Cmc of each copolymer was determined by fluorescence using the probe N-phenyl-1-naphthylamine (NPN), and the values are consistent with the particular chemical structure of each one. These findings can be useful in future studies of dependence of cmc on the chemical structure and solution conditions and to tailor polymers with specific properties and applications, making the cmc determination faster and more accurate. To the best of our knowledge, this it the first time that NPN is used to determine the cmc of this kind of positively charged copolymers.     

Synthesis of Allylester Resin Tethered to Layered Silicates by <Emphasis Type="Italic">in-situ</Emphasis> Polymerization and Its Nanocomposite

Summary Allylester resin tethered to layered silicate was synthesized by in-situ polymerization method and was cured by tert-butylperbenzoate (TBPB) directly. We ascertained the existing of carbonyl and benzyl groups which come from diallyl terephtalate in the gallery of layered silicates using the thermogravimetric analysis (TGA) and FT-IR. The residual weight and new IR peaks of the clay, which is treated by in-situ polymerization, imply that the hydroxy group of intercalant takes part in the polymerization of allylester resin. Also, its nanocomposite was characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns and TEM photographs indicate that the basal spacing (d ₀₀₁ ) of the nanocomposite made by in-situ polymerization is larger than those of the nanocomposite made by a simple mixing. Received: 3 October 2002/Revised version: 2 December 2002/Accepted: 3 December 2002 Correspondence to Seok-Ho Hwang     

Effects of phenyl-based pendent groups on helical conformation of poly(<Emphasis Type="Italic">N</Emphasis>-propargylamides)

Five achiral N-propargylamide monomers with various phenyl-based substitutents, [HC ≡ CCH₂NHCOR, R for M1: C₆H₄CH₃; M2: C₆H₄CH₂CH₃; M3: C₆H₄(CH₂)₂CH₃; M4: C₆H₄(CH₂)₃CH₃; M5: C₆H₄C(CH₃)₃], were synthesized and polymerized with a rhodium catalyst, (nbd)Rh⁺B^-(C₆H₅)₄ (nbd = 2,5-norbornadiene). The corresponding five homopolymers were obtained in high yields of 90–95% and with moderate molecular weights (M _n ≥ 10 000). All the polymers possessed high cis contents (≥95%). Poly(1)–poly(3) exhibited UV-vis absorption peaks at approx. 350 nm, which indicates that the three polymers formed helical conformations, while no UV-vis absorption peaks could be observed in poly(4) and poly(5) in the wavelength range of 320–500 nm, demonstrating that these two polymers could not adopt helical structures under the examined conditions. To confirm the helical structures formed in poly(1)–poly(3), a chiral monomer, M6, was utilized to copolymerize with M2, which was used as the representative for M1−M3. M6 was utilized since its polymer could form stable helices under suited conditions. The resulting copolymers exhibited remarkable CD effects, however, the maximum wavelength in the copolymers varied remarkably, mainly depending on the composition of the copolymers. It is concluded that in the formation of ordered helical conformations, the substitutents of varied bulk led to different steric repulsion and varied synergic effects among the neighboring pendent groups.     

Synthesis and gas permeability of poly(<Emphasis Type="Italic">p</Emphasis>-phenyleneethynylene)s having bulky alkoxy or alkyl groups

Dipropynylbenzene with branched alkoxy and alkyl groups [CH₃C≡CRC₆H₂RC≡CCH₃, R = 2-methylpropoxy (1a), 3-methylbutoxy (1b), 4-methylpentoxy (1c), cyclohexylmethoxy (1d), 2-ethylhexoxy (1e), 2-octoxy (1f), 2-ethylhexyl (1g), and 2-octyl (1h)] were polymerized with Mo(CO)₆ in the presence of 4-(trifluoromethyl)phenyl to afford poly(2,5-di(alkoxy or alkyl)-p-phenyleneethynylene)s (2a–h). Polymer 2a was insoluble in any solvents, but the other polymers (2b–h) were soluble in common organic solvents. The polymers with relatively long side chains (2e–h) had high molecular weight over 1.6 × 10⁴ and gave free-standing membranes by solution-casting method. The densities of membranes of 2e–h were 0.914–0.998, and their fractional-free volume values were relatively large (0.094–0.158). The oxygen permeability coefficients of membranes of 2e–h were 18.4, 12.7, 4.85, and 19.3 barrers, respectively. It was found that poly(p-phenyleneethynylene) with 2-octyl side groups, which have the branch at the nearest position from main chain, exhibited the highest gas permeability.     

Preparation of Tethered Half-Titanocene Complex on Syndiotactic Poly(styrene-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="Italic">p</Emphasis>-methylstyrene) for Using in Syndiospecific Polymerization of Styrene

Abstract  

In this work the syndiotactic polystyrene copolymer, poly (styrene-co-p-methylstyrene) was prepared by the copolymerization of styrene and p-methylstyrene with cyclopentadienyltitanium trichloride/methylaluminoxane catalyst. This copolymer was functionalized with silyl-hydride groups. The structure of copolymer and functionalized copolymer were characterized by FT-IR, ¹H-NMR and ¹³C-NMR spectroscopy. The obtained results revealed that the functionalization reaction successfully proceeds at low temperatures. Tethering of half-titanocene complex on polymeric support was done by the hydrosilylation reaction of 1-allylindenyltrichlorotitanium with silyl-hydride functionalized copolymer in the presence of Karstedt catalyst as a coupling reagent. The polymer-supported catalyst was tested for syndiospecific polymerization of styrene using methylaluminoxane as a cocatalyst. The results of styrene polymerization showed that the polymer-supported catalyst exhibited high activity for syndiospecific polymerization of styrene. The polymer prepared with supported catalyst was characterized by carbon nuclear magnetic resonance (¹³C-NMR) and differential scanning calorimetry (DSC). The results confirmed the syndiotacticity of obtained polymers. X-ray diffraction (XRD) analysis showed the δ-form crystalline structure of obtained syndiotactic polystyrene.     

Electrochemical oxidation of <Emphasis Type="Italic">p</Emphasis>-sulfonated calix[8]arene

The water-soluble p-sulfonated sodium salt of calix[8]arene (III) was synthesized. The product was characterized by FT-IR, NMR and UV–Vis spectra.Then the electrochemical behaviors of p-sulfonated sodium salt of calix[8]arene in NaAc+HAc (pH = 4) buffer solution was studied. In aqueous solution, p-sulfonated calix[8]arene can be oxidized when the potential is more than 0.7 V vs SCE. It was confirmed that the reaction was a two-electron irreversible electrochemical reaction. The transfer coefficient, α, was measured as 0.7. At 25°, the diffusion coefficient of p-sulfonated calix[8]arene was determined as 8.6 × 10⁻⁷ cm² s⁻¹. The diffusion activation energy of p-sulfonated calix[8]arene was 18.9 kJ mol⁻¹ at pH = 4.     

Electrochemical behavior of a new <Emphasis Type="Italic">s</Emphasis>-triazine-based dendrimer

The electrochemical behavior of a new G-2-s-triazine-based dendrimer, 2,4,6-tris-{4-{4,6-bis-{4-{4,6-bis-[(1S,2S)-1,3-dihydroxy-1-(4-nitrophenyl)-prop-2-ylamino]-s-triazin-2-yl}-piperazin-1-yl}-s-triazin-2-yl}-piperazin-1-yl}-s-triazine, (I), was studied in dimethylsulfoxide solution by cyclic voltammetry, on platinum and graphite electrodes. The electrochemical properties of I were compared with that of one of its precursor, N-{4,6-bis{4-{4,6-bis[(1S,2S)-1,3-dihydroxy-1-(4-nitrophenyl)-prop-2-ylamino]-s-triazin-2-yl}-piperazin-1-yl}-triazin-2-yl}-piperazine), (II), together with that of the starting material, (1S,2S)-2-amino-1-(4-nitrophenyl)-propane-1,3-diol (“p-nitrophenylserinol”), (III).     

Biparental Endowment of Endogenous Defensive Alkaloids in <Emphasis Type="Italic">Epilachna paenulata</Emphasis>

Coccinellid beetles contain a variety of defensive alkaloids that render them unpalatable to predators. Epilachna paenulata (Coleoptera: Coccinellidae) is a South American ladybird beetle that feeds on plants of the Cucurbitaceae family. The defensive chemistry of E. paenulata has been characterized as a mixture of systemic piperidine, homotropane, and pyrrolidine alkaloids. Whole body extracts of adult beetles contain four major alkaloids: 2-(2′-oxopropyl)-6-methylpiperidine (1); 1-(6-methyl-2,3,4,5-tetrahydro-pyridin-2-yl)-propan-2-one (2); 1-methyl-9-azabicyclo[3.3.1]nonan-3-one (3); and 1-(2″-hydroxyethyl)-2-(12′-aminotridecyl)-pyrrolidine (4). Comparative studies of the defensive chemistry of eggs, larvae, pupae, and adults showed differences in alkaloid composition and concentration among life stages. While adults contained mainly the homotropane 1-methyl-9-azabicyclo[3.3.1]nonan-3-one (3), eggs showed the highest concentration of the piperidine 2-(2′-oxopropyl)-6-methylpiperidine (1). We studied the origin of this alkaloid in the eggs by feeding newly emerged, virgin adult beetles with [2-¹³C]-labeled acetate, and by performing crosses between ¹³C-fed and unlabeled males and females. GC-MS analysis of alkaloids from ¹³C-fed males and females showed high incorporation of ¹³C into the alkaloids, as evidenced from a 20–30% increase of isotopic peaks in diagnostic fragment ions, confirming the expected endogenous origin of these alkaloids. In addition, analyses of eggs from different crosses showed that labeled alkaloids from both parents are incorporated into eggs, indicating that E. paenulata males transfer alkaloids to the females at mating. Biparental endowment of chemical defenses into eggs has been shown previously in insects that acquire defensive compounds from dietary sources. To our knowledge, this is the first report of biparental egg endowment of endogenous defenses. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of <Emphasis Type="Italic">Isotactic</Emphasis> Rich Poly(methylphenylsiloxane) by Living Anionic Ring-Opening Polymerization

Linear poly(methylphenylsiloxane) (PMPS) was prepared by the living anionic ring-opening polymerization of cis-2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane (cis-P₃). The resulting linear PMPS was shown by NMR to be highly stereoregular and remarkably high in meso-meso fraction and proposed isotactic content (~80%). Tetrahydrofuran (THF) was used as the solvent and it is noted that THF also acts as a promoter for the system by increasing the reactivity of the silanolate nucleophile at the end of the propagating chain. It is proposed that this increase in the reactivity occurs preferentially in the intermolecular (propagating) reaction. The evidence for this proposed hypothesis is the exclusive production of meso-meso and meso-racemic triads in the linear PMPS as evidenced by NMR. As the reaction temperature was increased, the rate of polymerization increased and yet the tacticity of the polymer was not affected. It is therefore clear that there was no significant amount of back-biting (intramolecular) reaction for the temperatures and time intervals studied here, despite the fact that ring-chain equilibration is commonly observed in ring-opening siloxane polymerizations. Had the reversion reaction been present, then scrambling of the chain stereoregular sequences would have been observed by an equilibration mechanism. It is well established that phenyl-phenyl interactions (π–π stacking) can stabilize certain local conformations in PMPS chains and hence we propose that these phenyl-phenyl interactions may prevent back-biting reactions for PMPS under the kinetic conditions employed here.     

Synthesis of <Emphasis Type="Italic">p</Emphasis><Emphasis Type="Bold">-</Emphasis> and <Emphasis Type="Italic">n</Emphasis>-type Gels Doped with Ionic Charge Carriers

In this study, we synthesized the new kinds of semiconducting polymeric gels having negative (n-type) and positive (p-type) counter ions as charge carriers. The polyacrylamide gel was doped with pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt), having \textSO₃ ^- {\text{SO}}_{3}^{ - } ions as side groups and Na⁺ as counter ions, so-called p-type semiconducting gel. The doping process was performed during the polymerization where the pyranine binds to the polymer strands over OH group chemically via radical addition. In a similar way, N-isopropylacrylamide (NIPA) gel was doped with methacrylamidopropyltrimethyl ammonium chloride (MAPTAC), having Cl⁻ as counter ions, so-called n-type semiconducting gel. Here MAPTAC was embedded by copolymerization within the polymer network (NIPA). These semiconducting gels can show different electrical properties by changing the concentration of the doping agents, swelling ratio etc. We have shown that the pn junction, formed by combining p-type and n-type gels together in close contact, rectifies the current similar to the conventional Si and Ge diodes.     

Synthesis of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) by ATRP using a fluorescein-based initiator

Summary A new fluorescent initiator fluorescein 2-bromoisobutyrate (Flu-Br) was synthesized. The use of Flu-Br as initiator, Me₆TREN as ligand and CuCl as catalyst by atom transfer radical polymerization allowed for chain-end fluoresceined poly(N-isopropylacrylamide) (Flu-PNIPAM) in one step. The polymerization reached high conversion (65%) and low polydispersity (PDI) (1.15∼1.28). The linearity plot of the M_n,GPC and M_n,NMR against conversion and the low PDI revealed the well-controlled polymerization by ATRP. In addition, N-isopropylacrylamide (NIPAM) was copolymerized with hydrophilic N,N-dimethylacrylamide (DMAM) using Flu-Br initiator by ATRP. By changing the feed ratio of NIPAM to DMAM, it was very easy to obtain thermo-sensitive fluorescent copolymers with proper lower critical solution temperature (36.0±0.2 °C, 38.0±0.2 °C). The pH dependence on fluorescence intensity of Flu-PNIPAM displayed a similar behavior to the parent fluorescein.     

On the Chemical Origin of the Gap Bowing in (GaAs)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript> Alloys: A Combined DFT–QS<Emphasis Type="Italic">GW</Emphasis> Study

Motivated by the research and analysis of new materials for photovoltaics and by the possibility of tailoring their optical properties for improved solar energy conversion, we have focused our attention on the (GaAs)_{1− x} Ge_2x series of alloys. We have investigated the structural properties of some (GaAs)_{1− x} Ge_2x compounds within the local-density approximation to density-functional theory, and their optical properties within the Quasiparticle Self-consistent GW approximation. The QSGW results confirm the experimental evidence of asymmetric bandgap bowing. It is explained in terms of violations of the octet rule, as well as in terms of the order–disorder phase transition.     

Adsorption of Bovine Serum Albumine Onto Poly (<Emphasis Type="Italic">N</Emphasis>-<Emphasis Type="Italic">t</Emphasis>-Butylacrylamide-co-Acrylamide/Maleic Acid) Hydrogels

In the present study, a series of ionic poly(N-t-butylacrylamide-co-acrylamide) [P(NTBA-co-AAm)] hydrogels were synthesized by free-radical crosslinking copolymerization of N-t-butylacrylamide (NTBA) and acrylamide (AAm) monomers in fixed amount, but changing amount of maleic acid (MA) comonomer in methanol using N,N-methylene-bis-acrylamide (BAAm) as the crosslinker, ammonium persulfate (APS) as the initiator, and N,N,N′,N′-tetramethylethylenediamine (TEMED) as the activator. The swelling behavior of these hydrogels was analyzed in buffer solutions at various pHs. The prepared hydrogels also were investigated swelling-deswelling transition in water depending on the temperature. For the bovine serum albumin (BSA) adsorption, the effect of pH, temperature, initial protein concentration and adsorption rate were investigated. Maximum BSA adsorption was observed at pH 5.0 which is close to the isoelectric pH of BSA (pH 4.8). The highest adsorption rate was achieved in about 12 h. and also, maximum BSA adsorption was found at +5°C.     

Preparation of gold nanoparticles under presence of the diblock polyampholyte PMAA-<Emphasis Type="Italic">b</Emphasis>-PDMAEMA

The preparation of gold nanoparticles in presence of different weak polyampholytes is investigated. As diblock polyampholytes several poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), PMAA-b-PDMAEMA, have been used, characterized by different molecular weight and block ratio. HAuCl₄ is used as gold precursor where LiBH₄ is acting as reductive agent to obtain the gold nanoparticles. The addition of gold precursors to aqueous solutions of PMAA-b-PDMAEMA polyampholytes leads to an acidification of the solution resulting in a change of the polyampholyte conformation through protonation of the PDMAEMA blocks. This modification of polyampholyte conformation also allows the tuning of the size and size distribution of the accordingly formed gold nanoparticles. Investigations presented, are performed mainly by AFM of the systems in thin film adsorbed on native oxide-terminated Si substrate. TEM was used to reveal the change in size of the obtained gold nanoparticles.     

Swelling characterization of poly (acrylamide-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="Italic">N</Emphasis>-vinylimidazole) hydrogels crosslinked by TMPTA and semi-IPN’s with PEG

In this study, a novel semi-interpenetrating network (semi-IPN’s) hydrogel, composed of acrylamide (AAm) with N-vinylimidazole (NVI) as comonomer, with poly (ethylene glycol)(PEG) and a multifunctional crosslinker such as trimethylolpropane triacrylate (TMPTA) was prepared. Highly swollen poly (AAm/NVI) hydrogels and semi-IPN’s were synthesized by free radical solution polymerization. Swelling experiments were performed in water at 25°C, gravimetrically. The influence of NVI and PEG content in hydrogels were examined. Poly (AAm/NVI) and poly (AAm/NVI/PEG) hydrogels showed large extents of swelling in aqueous media the swelling being highly dependent on the chemical composition of the hydrogels. Swelling ratio of poly (AAm/NVI) hydrogels and poly (AAm/NVI/PEG) hydrogels was shown 7.16–39.85. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non-Fickian in character. This study has given the quantitative information on the swelling characteristic of poly (AAm/NVI) hydrogel and semi-IPN’s as water absorbent in many potential applications.