Structure Of Polymer Chains Research Articles

Preparation of novel polymer-metal oxide nanocomposites with nanophase separated hierarchical structure

This article deals with preparation of nanocomposite which comprised of nanophase separated structure of polymer chains and metal oxide. By grafting poly(hydroxyethyl methacrylate), poly(HEMA) on the surface of titanium which is covered by passive titanium oxide by atom transfer radical polymerization (ATRP) and executing anodic polarization, hierarchy nanophase separated structure with controlled thickness can be obtained. The titanium ions would be cationically charged and completely filled up the unoccupied binding sites of the polymer chains via electrochemical reaction, eventually covering the polymer chains with titanium oxide. However, this structure can be obtained when the anodic polarization is executed at initial applied voltage exceeding 10 VSCE. The control of thickness is possible by controlling the initial applied voltage. These results prove that the conventional polymer can form composite structure with metal oxide without using fillers or special polymers designed for composite.

Microwave Assisted Synthesis of Poly(ether sulfone) – An Efficient Synthetic Route to Control Polymer Chain Structure

A novel synthetic process for the efficient control over molecular weight of the poly(ether sulfone) has been studied. The application of microwave irradiation for the condensation polymerization to synthesize poly(ether sulfone) is demonstrated. Microwave assisted polymerization results in significant reduction of reaction time. Microwave based process is also feasible at lower temperature for the synthesis of poly(ether sulfone). Polymers synthesized have been characterized using NMR and FTIR spectroscopy. Polymer film morphology and surface composition have been studied using SEM and EDX. An increase in the molecular weight is observed with increasing microwave irradiation time.

Electrical conductivity and optical properties of a new quaternized polysulfone

Quaternized polysulfone with triphenylphosphonium pendant groups was investigated, as to its optical and electronic properties. Optical properties were analyzed by refractivity and transmission spectra. To obtain the optical parameters, the approach proposed by Tauc for amorphous semiconductors has been used, because of the similarity of the absorption edges. Values of pseudogap energy and Urbach energy of 3.89 eV and 168 meV, respectively, were obtained. The dielectric properties and AC-conductivity were also studied as a function of temperature and frequency. Decrease in the dielectric constant was observed with the increase in frequency and decrease in temperature. Also, quaternized polysulfone films were characterized by two relaxation processes, γ and β relaxation, which appear at different temperatures, depending on the pendant group. The frequency–temperature-dependent conductivity showed that conductivity increases with frequency and also that the quaternized polysulfones possess typical semiconducting properties. All parameters have been found as slightly influenced by the polymer chain structure.

Synthesis of porphyrin‐end‐functionalized polycyclohexane with well‐controlled and defined polymer chain structure

AbstractTetraphenylporphyrin‐end‐functionalized polycyclohexane (H2TPP‐PCHE) and its metal complexes (MTPP‐PCHE) were synthesized as the first successful example of porphyrin‐end‐functionalized transparent and stable polymers with a well‐controlled and defined polymer chain structure. Chloromethyl‐end‐functionalized poly(1,3‐cyclohexadiene) (CM‐PCHD) was synthesized as prerequisite prepolymer by the postpolymerization reaction of poly(1,3‐cyclohexadienyl)lithium and chloro(chloromethyl)dimethylsilane. CM‐end‐functionalized PCHE (CM‐PCHE) was prepared by the complete hydrogenation of CM‐PCHD with p‐toluenesulfonyl hydrazide. H2TPP was incorporated onto the polymer chain end by the addition of 5‐(4‐hydroxyphenyl)‐10,15,20‐triphenylporphyrin to CM‐PCHE. The complexation of H2TPP‐PCHE and Zn(OAc)2 (or PtCl2) yielded a zinc (or platinum) complex of H2TPP‐PCHE. H2TPP‐PCHE and MTPP‐PCHE were readily soluble in common organic solvents, and PCHE did not inhibit the optical properties of the H2TPP, ZnTPP, and PtTPP end groups. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Polyethylenimine Containing Benzimidazole Branching: A Model System Providing a Balance of Hydrogen Bond Network or Chain Mobility Enhances Proton Conductivity

A series of multibenzimidazole functionalized branched polyethylenimine (MPEI) molecules with varied benzimidazole substitution are designed and synthesized to study how hydrogen bonds of benzimidazole can be enhanced through the branching structure of polymer chains. The reduction of H-bonding and the increment of interatomic distance distribution initiate an increase in proton conductivity with temperature as detailed analyses by temperature dependence Fourier transform infrared spectroscopy and radial distribution function calculated from temperature dependence X-ray diffraction technique. MPEIs with a higher benzimidazole substitution form a greater number of hydrogen bonds together with the lowering of chain mobility. In combination with the proton conductivity evaluation, bPEI with 19.7% benzimidazole substitution is a preferable condition since at this condition both hydrogen bond and chain mobility are in good balance and favor the proton transfer resulting in a significant proton conductivity ∼10(-5) S cm(-1) in the case of the pure sample in pellet form and ∼10(-4) S cm(-1) in the case of the blend with PVA in the membrane form measuring at 190 °C under anhydrous condition.

Elastic modulus of nanostructured polymer surfaces

Living cell cultures exhibit improved adhesion on polymer surfaces engineered with nano-scale structures as compared to their flat counterparts. During fabrication their polymer-chain structure can be altered, thus affecting their mechanical properties. Here, we demonstrate using atomic-force-microscope nanoindentation that the modulus of nanostructured PDMS is doubled, while that of nanostructured ORMOCER increases by an order of magnitude, when compared to their flat counterparts.

Effects of Base Polymer Hydrophobicity and End-Group Modification on Polymeric Gene Delivery

A new 320-member polymer library of end-modified poly(β-amino ester)s was synthesized. This library was chosen such that small differences to the structures of component backbone, side-chain, and end-group monomers could be systematically and simultaneously evaluated. The in vitro transfection efficacy and cytotoxicity of DNA nanoparticles formed from this library were assessed. This library approach not only enabled us to synthesize and test a large variety of structures rapidly but also provided us with a robust data set to analyze for the effect of small structural permutations to polymer chain structure. Small changes to the side chains, backbones, and end groups within this polymer library produced dramatic results, with transfection efficacy of CMV-Luc varying over 4 orders in a 96-well plate format. Increasing hydrophobicity of the base polymer backbone and side chain tended to increase transfection efficacy, but the most hydrophobic side chains and backbones showed the least requirement for a hydrophobic pair. Optimal PBAE formulations were superior to commercially available nonviral alternatives FuGENE HD and Lipofectamine 2000, enabling ~3-fold increased luminescence (2.2 × 10(6) RLU/well vs 8.1 × 10(5) RLU/well) and 2-fold increased transfection percentage (76.7% vs 42.9%) as measured by flow cytometry with comparable or reduced toxicity.

3D Single Cyclized Polymer Chain Structure from Controlled Polymerization of Multi-Vinyl Monomers: Beyond Flory–Stockmayer Theory

Controlled/living radical polymerization (CRP) is a widely used technique that allows the synthesis of defined polymer architectures through precise control of molecular weights and distributions. However, the architectures of polymers prepared by the CRP techniques are limited to linear, cross-linked, and branched/dendritic structures. Here, we report the preparation of a new 3D single cyclized polymer chain structure from an in situ deactivation enhanced atom transfer radical polymerization of multivinyl monomers (MVMs), which are conventionally used for the production of branched/cross-linked polymeric materials as defined by P. Flory and W. Stockmayer nearly 70 years ago. We provide new evidence to demonstrate that it is possible to kinetically control both the macromolecular architecture and the critical gelling point in the polymerization of MVMs, suggesting the classical Flory-Stockmayer mean field theory should be supplemented with a new kinetic theory based on the space and instantaneous growth boundary concept.

Preparation of optically active poly(N-propargylamide) gels and their application in chiral recognition

Optically active gels based on helical N-propargylamide polymers were prepared using a one-pot two-step methodology: the pre-formation of helical N-propargylamide copolymer (defined as N=N-HP) and the preparation of gels bearing the helical copolymers. To prepare N=N-HP, N-propargylamide M1, which contained -N=Nfunctional group, and M2, which provided helical polymer chains for the resulting copolymers, underwent copolymerizations in the presence of (nbd)Rh+B-(C6H5)4 as a catalyst. -N=N- groups in N=N-HP acted as an initiator to induce the free radical polymerization of styrene, yielding the designed gels. Trimethylol propane triacrylate (TMPTA) was used to improve the cross-linking degree of the gels. The obtained gels were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and circular dichroism (CD) spectroscopy measurements. The gels showed high optically activity, resulting from the helical structures of the N-propargylamide polymer chains. Preferential adsorption towards (R)-(+)-1-phenylethylamine in the two enantiomers was observed in the obtained gels, demonstrating the potentials of such gels in chiral recognition and chiral resolution. Open image in new window

Optical, Dielectric, and Conduction Properties of New Phosphorus-Modified Polysulfones

New phosphorus-modified polysulfones with different substitution degrees, obtained from chloromethylated polysulfones, were analyzed in terms of their optical, dielectric, and conduction properties. In order to obtain the optical parameters, the approach proposed by Tauc for amorphous semiconductors was used.[ 23 , 24 ] The determined parameters were found to be related to the influence of the polymer chain structure and the history of films’ preparations. The temperature and frequency dependence of dielectric constant and dielectric relaxation were investigated by AC-dielectric measurements. The nature of the relaxation mechanisms was established on the basis of the dielectric measurement results. The samples displayed two sub-glass relaxations, i.e. γ relaxation – where the activation energy changes insignificantly with the substitution degree, and β relaxation – with higher apparent activation energy for lower substitution degrees. The results obtained from Tauc's law and AC-conduction studies indicated that the conduction mechanism in the phosphorus-modified polysulfone was due to electronic hopping, and that a model based on the energy bandgap representation could be suitable for explaining the temperature dependence of electrical conductivity.

Annealing Effect on Photovoltaic Performance of Hybrid P3HT/In-Situ Grown CdS Nanocrystal Solar Cells

The CdS nanocrystals with different aspect ratios (ARs) can be synthesized directly in the presence of conjugated polymer poly(3-hexylthiophene-2,5-diyl) (P3HT). The UV-vis spectra of the composite films show a blue shift of the π-π* transition band with an increasing aspect ratio (AR) of the CdS nanocrystals, which was attributed to the destruction of the ordered structure of polymer chains as supported by PL measurements. Atomic force microscope measurements on P3HT/CdS film also demonstrate the aggregation of CdS nanocrystal in the P3HT matrix is more apparent for the CdS nanocrystals of AR = 4 than that of AR = 16, indicating a stronger interaction between P3HT and CdS for a larger AR (16), which is favorable for the network structure and formation of percolation paths to increase the transport properties of the P3HT/CdS solar cells. Therefore, a higher power conversion efficiencies (PCE) up to 2.95% can be obtained for the in-situ-grown P3HT/CdS with AR = 16 upon annealing treatment at 160°C for 60 min.

CdS-containing nano-assemblies of double hydrophilic block copolymers in water

Two samples of poly(sodium(sulfamate-carboxylate)isoprene)-block-poly(ethylene oxide) copolymer (SCIEO-1 and SCIEO-2) differing in molecular weight and relative length of polyelectrolyte blocks have been used as templates for the synthesis of cadmium sulfide (CdS) nanoparticles in aqueous media. The double-hydrophilic copolymer SCIEO has very high 1D charge density, and its polymer chain structure mimics that of polysaccharide heparin. It is soluble in aqueous media, but the addition of cadmium acetate (Cd(Ac)2) to its aqueous solution causes the formation of micellar aggregates with Cd2+containing insoluble cores above the threshold Cd2+ concentration. The trapped Cd2+ ions can be chemically transformed to CdS nanoparticles. The stability of hybrid SCIEO/CdS micelles depends on the ratio of PEO-to-SCI lengths: it was found that the SCIEO-2 copolymer with sufficiently long PEO block behaves as an effective stabilizer for the synthesis of CdS nanoparticles embedded in micelles, while SCIEO-1 does not. The morphology of aggregates varies with the Cd-to-SCI ratios and ranges from spherical to mixture of spherical and necklace-like micellar aggregates. A number of experimental techniques including static and dynamic light scattering, fluorescence correlation spectroscopy, atomic force and transmission electron microscopy, UV-vis, and fluorescence spectroscopy were employed for the characterization of both CdS containing hybrid micelles and embedded CdS nanoparticles.

Novel hyperbranched polyphenylsilsesquioxane‐modified cyanate ester resins with improved toughness and stiffness

AbstractHigh‐performance thermosetting resins should have good toughness and stiffness, so simultaneously toughening and stiffening is the main target in developing high‐performance resins. A novel modified cyanate ester resin with improved toughness and stiffness was developed by copolymerizing 2,2′‐bis(4‐cyanatophenyl)isopropylidene (CE) with hyperbranched polyphenylsilsesquioxane (HBPPSi). The mechanical properties and their nature were systematically investigated from the viewpoint of structure‐property relations using positron annihilation lifetime spectroscopy and spectral analyses. It is found that a suitable content of HBPPSi in CE resin can effectively improve toughness and stiffness. In the case of the CE resin modified with 10 wt% HBPPSi, its impact and flexural strengths are 21 kJ m−2 and 148 MPa, respectively, about 2.6 and 1.4 times of those of neat CE resin. The flexural modulus increases from 3.0 (for neat CE resin) to 3.4 GPa. The results of dynamic mechanical analyses also corroborate the static mechanical properties. The improved toughness and stiffness of CE resin can be attributed to the synergistic effect resulting from changes of both polymer chain structure and aggregation state structure. These attractive features of HBPPSi/CE resins suggest that the method proposed herein may be a new approach for the development of high‐performance resins for cutting‐edge industries. Copyright © 2011 Society of Chemical Industry

Spectroscopy of Nano-Sized Polysilanes Confined by Different Structures of Silica

Four novel nanocomposite films based on poly(di-n-hexylsilane) (PDHS) incorporated into an inorganic matrix having different structure are fabricated. Polymer chains are localized into the nanopores of SiO2 and TiO2 films, between globules of photonic crystals, as well as in the matrix of nano-sized SiO2 particles. Photoelectronic properties of the composites have been studied using fluorescence (FL) and FL decay measurements in a wide temperature range (5–330) K. The temperature dependence of FL intensities enabled us to establish the nature of a conformational structure of polymer chains, as well as to obtain information about the thermochromic transition of confined PDHS and the excitation energy transfer pathways.

Synthesis of poly(p -phenylene)-poly(4-diphenylaminostyrene) bipolar block copolymers with a well-controlled and defined polymer chain structure

A poly(p-phenylene) (PPP)-poly(4-diphenylaminostyrene) (PDAS) bipolar block copolymer was synthesized for the first time. A prerequisite prepolymer, poly(1,3-cyclohexadiene) (PCHD)-PDAS binary block copolymer, in which the PCHD block consisted solely of 1,4-cyclohexadiene (1,4-CHD) units, was synthesized by living anionic block copolymerization of 1,3-cyclohexadiene and 4-diphenylaminostyrene. To obtain the PPP-PDAS bipolar block copolymer, the dehydrogenation of this prepolymer with quinones was examined, and tetrachloro-1,2-(o)-benzoquinone was found to be an appropriate dehydrogenation reagent. This dehydrogenation reaction was remarkably accelerated by ultrasonic irradiation, effectively yielding the target PPP-PDAS bipolar block copolymer. The hole and electron drift mobilities for PPP-PDAS bipolar block copolymer were both on the order of 10−3 to 10−4 cm2/V·s, with a negative slope when plotted against the square root of the applied field. Therefore, this bipolar block copolymer was found to act as a bipolar semi-conducting copolymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Opto-electrical properties of some quaternized polysulfones

A novel quaternized polysulfone with N-dimethylethylammonium chloride (DMEA) and N-dimethyloctylammonium chloride (DMOA) pendent groups was investigated, as to its optical and electronic properties. Optical properties were investigated by refractivity and transmission spectra. To obtain the optical parameters, the approach proposed by Tauc for amorphous semiconductors has been used, because of the similarity of the absorption edges. The values of pseudogap energy ranged between 3.60 and 3.69 eV, while those of Urbach energy were modified over the 157—172 meV range. The dielectric properties and ac-conductivity were also studied as a function of temperature, frequency and structure of pendant groups. It was observed that the dielectric constant decreased as the frequency increased and the temperature decreased. In addition, quaternized polysulfone films were characterized by two relaxation processes, i.e., γ and β relaxation, which appeared at different temperatures, depending on the pendant groups. The frequency—temperature-dependent conductivity showed that conductivity increased with frequency and also that the quaternized polysulfones possessed typical semiconducting properties. All parameters were found to be slightly influenced by the polymer chain structure.

Effect of thermal annealing on the efficiency of poly (3-hexylthiphone):[6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester bulk heterojunction solar cells

The effect of thermal annealing on the performance of bulk heterojunction poly (3-hexylthiphone) (P3HT): (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) solar cells has been examined. We found that the efficiency of the solar cell increases from 0.08% to 3.81% as the annealing temperature is varied from room temperature to 120 ◦ C. This improvement in the efficiency is due to the rearrangement of polymer molecules and nanoparticles. Annealing reorders the P3HT polymer chain structure (which was ruined by the PCBM nanoparticles) by segregating out PCBM molecules from polymer. Due to annealing, movement in the P3HT and PCBM particles is induced, which reorganize and form a phase segregated 3D structure of donor and acceptor molecules enhancing the charge transfer efficiency. It also improves the surface morphology and polymer chain interconnections resulting in enhancement of hole mobility through the polymer network. C 2011 Society of Photo-Optical Instrumentation Engineers

Study of PEDOT conductive polymer films by admittance measurements

In this paper we propose the use of a microwave technique to measure the conductivity of poly(3,4-ethylenedioxythiophene) (PEDOT) films. The PEDOT layers were prepared by electropolymerization from aqueous solutions using both poly(sodium 4-styrene sulphonate) (NaPSS) and sodium dodecyl sulphate (NaDS) acting as monomer solubilizer and dopant for the polymer. The conductive properties of a series of samples produced under different synthesis conditions and characterized by different structures have been investigated by microwave measurements in the frequency range from 40 MHz to 40 GHz by using a Corbino disc geometry. Such technique allows to estimate the mean conductivity of the polymer samples overcoming the limitations of the measuring configurations typically imposed by the conventional d.c. measurements. The morphology of PEDOT films and the structure of polymer chains were studied by scanning electron microscopy (SEM) and Raman spectroscopy, respectively. The correlated morphological, structural and microwave analysis enabled us to evidence several factors that affect the macroscopic scale conductivity of the polymer sample films and to identify the conditions for preparation of PEDOT films with functional properties relevant to technological applications.

Ultrasound‐accelerated dehydrogenation of poly(1,3‐cyclohexadiene): efficient synthesis of poly(para‐phenylene)

AbstractThe effect of ultrasonication on the dehydrogenation of poly(1,3‐cyclohexadiene) (PCHD) with benzoquinones was examined with the aim of improving the rate of reaction at moderate temperature. The type of solvent and the ultrasound treatment strongly affected the dehydrogenation of PCHD. The rate of reaction of the dehydrogenation of PCHD with 2,3‐dichloro‐5, 6‐dicyano‐1,4‐benzoquinone (DDQ) or 3,4,5,6‐tetrachloro‐1,2‐(o)‐benzoquinone (TOQ) was markedly improved by the use of ultrasound, and poly(para‐phenylene) (PPP) and PPP–TOQ complex, respectively, were successfully obtained. The electron drift mobility for PPP was of the order of 10−4 cm2 V−1 s−1 with a negative slope, while that for PPP–TOQ complex was of the order of 10−3 to 10−4 cm2 V−1 s−1 with a negative slope. The dehydrogenation of PCHD with benzoquinones under ultrasonication is thus an effective method to obtain soluble PPP with a well‐defined polymer chain structure. Copyright © 2010 Society of Chemical Industry

Effect of polymer chain structure on electroluminescence of poly(4-diphenylaminostyrene)/Alq3 blend films

Three types of poly(4-diphenylaminostyrene) (PDAS) having different polymer chain structures were prepared by living anionic polymerization, and the electroluminescence of PDAS/tris(8-hydroxyquinoline) aluminum (Alq3) blend films was examined to obtain basic information of PDAS for application to organic light-emitting diodes (OLEDs). The hole drift mobility of PDAS was on the order of 10−4 to 10−5 (cm2 V−1 s−1) with a negative slope, and it increased with an increase in the syndiotactic configuration in the polymer chain. The current density, turn-on voltage and brightness were also improved with an increase in the syndiotactic configuration of PDAS. Three types of poly(4-diphenylaminostyrene) (PDAS) having different polymer chain structures were prepared by living anionic polymerization, and the electroluminescence of PDAS/tris(8-hydroxyquinoline) aluminum (Alq3) blend films was examined. The hole drift mobility of PDAS increased with an increase in the syndiotactic configuration. The current density, turn-on voltage and brightness were also improved with an increase in the syndiotactic configuration of PDAS.