High MW Polymers Research Articles

Unraveling the Molecular Weight Dependence of High Magnetic Field to Manipulate the Semiconducting Polymer Molecular Orientation.

The magnetic alignment of molecules, which exploits the anisotropy of diamagnetic susceptibility, provides a clean and versatile approach to the structural manipulation of semiconducting polymers. Here, the magnetic-alignment dynamics of two molecular-weight (MW) batches of a diketopyrrolopyrrole (DPP)-based copolymer (PDVT-8) were investigated. Microstructural characterizations revealed that the magnetically aligned, high-MW (Mn = 53.7 kDa) PDVT-8 film exhibited a higher degree of backbone chain alignment and film crystallinity compared with the low-MW (Mn = 17.6 kDa) PDVT-8 film grown via the same magnetic alignment method. We found that as the MW increases, the degree of preaggregation of the polymer molecules in solution significantly increases and the aggregation mode changes from H-aggregation to J-aggregation through a cooperative assembly mechanism. These events improved the responsiveness of high-MW polymer molecules to magnetic fields. Field-effect transistors based on the magnetic aligned high-MW PDVT-8 films exhibited a 6.8-fold increase in hole mobility compared to the spin-coated films, along with a mobility anisotropy ratio of 12.6. This work establishes a significant correlation among chain aggregation behavior in solution, polymer film microstructures, magnetic responsiveness, and carrier transport performance in donor-acceptor polymer systems.

Transport limitations in polyolefin cracking at the single catalyst particle level.

Catalytic cracking is a promising approach to chemically recycle polyolefins by converting them into smaller hydrocarbons like naphtha, and important precursors of various platform chemicals, such as aromatics. Cracking catalysts, commonly used in the modern refinery and petrochemical industry, are tailored to process gaseous or liquid feedstock. Polyolefins, however, are very large macromolecules that form highly viscous melts at the temperatures required to break their backbone C-C bonds. Therefore, mass transport is expected to limit the performance of traditional cracking catalysts when applied to the conversion of polymers. In this work, we study these effects during the cracking of polypropylene (PP) over catalysts utilized in the fluid catalytic cracking (FCC) process. Thermogravimetric experiments using PP of varying molecular weight (Mw) and catalysts of varying accessibility showed that low Mw model polymers can be cracked below 275 °C, while PP of higher Mw required a 150 °C higher temperature. We propose that this difference is linked to different degrees of mass transport limitations and investigated this at length scales ranging from milli- to nanometers, utilizing in situ optical microscopy and electron microscopy to inspect cut open catalyst-polymer composites. We identified the main cause of transport limitations as the significantly higher melt viscosity of high Mw polymers, which prohibits efficient catalyst-polymer contact. Additionally, the high Mw polymer does not enter the inner pore system of the catalyst particles, severely limiting utilization of the active sites located there. Our results demonstrate that utilizing low Mw polymers can lead to a significant overestimation of catalyst activity, and suggest that polyolefins might need to undergo a viscosity reducing pre-treatment in order to be cracked efficiently.

High Arctic biocrusts: characterization of the exopolysaccharidic matrix

Biocrusts can be found in a wide array of habitats, where they provide important ecosystem services. These microbial associations are particularly important in High Arctic environments, where biocrust colonize the newly exposed barren soil after glacier retreat and significantly contribute to soil stabilization and nutrient cycling. Starting from incipient, structurally simple biolayers, they develop in complexity, increasing from the glacier terminus. Starting from a simple community structure, mainly constituted by cyanobacteria, heterotrophic bacteria and fungi immersed in a self-secreted extracellular polymeric matrix (cyanobacterial crusts), they later may recruit mosses and lichens (moss crusts and lichen crusts, respectively). The extracellular polymeric matrix protects the biocrust community from abiotic constraints, notably drought and freezing stress, from external physical harming factors, and from predation. The physicochemical characteristics of the extracellular matrix are related to several of its properties, such as its soil-stabilizing effect and water retention. We analysed the chemical (monosaccharidic composition) and macromolecular (molecular weight distribution) properties of the extracellular polymeric matrix of biocrusts with different morphologies collected in northwestern Spitsbergen, Norway. The uronic acid content and molecular weight (MW) distribution of the extracellular polysaccharidic matrices (EPMs) appeared in accordance with the developmental stages of the biocrusts. The MW distribution also showed significant differences between the samples, possibly reflecting differences in microbial enzymatic activities leading to the degradation of high-MW polymers into smaller compounds. The MW distribution profiles presented some important differences, reflecting differences in environmental conditions and, probably, the seasonal variance in microbial community composition that is known to characterize the environment examined in the present study.

The Incorporation of Carvacrol into Poly (vinyl alcohol) Films Encapsulated in Lecithin Liposomes.

Lecithin-encapsulated carvacrol has been incorporated into poly (vinyl alcohol) (PVA) for the purpose of obtaining active films for food packaging application. The influence of molecular weight (Mw) and degree of hydrolysis (DH) of the polymer on its ability to retain carvacrol has been analysed, as well as the changes in the film microstructure, thermal behaviour, and functional properties as packaging material provoked by liposome incorporation into PVA matrices. The films were obtained by casting the PVA aqueous solutions where liposomes were incorporated until reaching 0 (non-loaded liposomes), 5 or 10 g carvacrol per 100 g polymer. The non-acetylated, high Mw polymer provided films with a better mechanical performance, but less CA retention and a more heterogeneous structure. In contrast, partially acetylated, low Mw PVA gave rise to more homogenous films with a higher carvacrol content. Lecithin enhanced the thermal stability of both kinds of PVA, but reduced the crystallinity degree of non-acetylated PVA films, although it did not affect this parameter in acetylated PVA when liposomes contained carvacrol. The mechanical and barrier properties of the films were modified by liposome incorporation in line with the induced changes in crystallinity and microstructure of the films.

Does Polymer's Viscoelasticity Influence Heavy-Oil Sweep Efficiency and Injectivity at 1 ft/D?

Summary For heavy-oil-recovery applications, mobility control is more important than interfacial-tension reduction, and therefore importance should be given to the recovery of remaining mobile oil by enhanced sweep efficiency. Although the relative roles of polymer viscosity and elasticity in capillary-trapped residual light-oil recovery have been studied extensively, their roles in sweeping mobile viscous oil have not been explored. Injectivity is vital for heavy-oil-recovery applications, and polymer selection is performed solely using criteria that is based on shear rheology. In this paper, the influence of viscous (shear) resistance and elastic (extensional) resistance of viscoelastic polymer on mobile-heavy-oil recovery and injectivity is investigated through the combination of bulk shear/extensional rheology and single-phase and multiphase coreflood experiments at a typical reservoir-flooding rate of 1 ft/D. Two polymer solutions with different concentrations and salinities are selected such that a polymer with low molecular weight (MW) [hydrolyzed polyacrylamide (HPAM) 3130] provides higher shear resistance than a high-MW polymer (HPAM 3630). Extensional characterization of these two polymer solutions performed using a capillary breakup extensional rheometer revealed that HPAM 3630 provided higher extensional viscosity than HPAM 3130. The results show that the behaviors of polymers in extension and shear are completely different. Two multiphase and two single-phase experiments are conducted at low flux rate to investigate the roles of extensional viscosity on mobile-heavy-oil recovery and high flux rates on injectivity. After 1 pore volume (PV) of polymer injections, higher-concentration and lower-MW HPAM 3130 contributes to approximately 17% higher incremental recovery factor vs. lower-concentration and higher-MW HPAM 3630. The core-scale pressure drop generated by HPAM 3130 is more than twice the pressure drop generated by HPAM 3630. Under low-flux-rate conditions at the core scale, shear forces dominate, and displacing fluid with higher shear viscosity contributes to better sweep. HPAM 3630 exhibits a shear-thickening phenomenon and possesses the apparent viscosity of approximately 90 cp at the flux rate of approximately 90 ft/D. In contrast, HPAM 3130 continued showing shear thinning and has the apparent viscosity of approximately 70 cp at approximately 90 ft/D. This signifies the role of extension rheology on the injectivity at higher flux rates. Results revealed that while the extensional rheological role toward sweeping the mobile heavy-oil recovery at low flux is lesser compared with the shear role, its negative role on the polymer injectivity is very significant. Polymer-selection criteria for heavy-oil-recovery applications should incorporate extensional rheological parameters.

Laboratory treatment of HPAM polymers for injection in low permeability carbonate reservoirs

Polymeric solutions are injected into petroleum reservoirs to improve sweep efficiency of enhanced oil recovery processes. Viscous polymeric solutions cannot be injected into non-fractured low permeability carbonates (k < 50 mD) if a significant fraction of pore throats is smaller than the polymer molecules. Mechanical shear degradation and aggressive microfiltration can be applied as tools to modify the molecular weight distribution (or hydrodynamic radius) of polymers. High speed mechanical shearing in a laboratory blender showed significant reduction in viscosity and polydispersity for the polymer stock solutions with improvement in filterability and transport in low permeability porous media. Aggressive filtration through small sized filter papers proved to be a good technique for refinement of molecular weight distribution and removing larger molecules for successful injection in low permeability carbonates. Dynamic light scattering (DLS) method was used to measure the size distribution of shear degraded polymer solutions at low concentrations. The optimum shear degradation required for a high MW polymer to be successfully injected into a low permeability carbonate reservoir was decided by comparing the polymer size distribution with the pore throat diameter distribution obtained from mercury injection capillary pressure (MICP) for the rock. This novel technique was successfully applied for injection of viscous polymer solutions in carbonates with permeability less than 20 mD. The pore throat distribution of a porous medium is more important than the permeability (or average hydraulic radius) for the transport of polymers in porous media.

Polyastaxanthin-based coatings reduce bacterial colonization in vivo

Polyastaxanthin p(ATX) is a family of polymers synthesized from the carotenoid astaxanthin and various dicarboxylic acids, resulting in moldable, high MW polymers, that can be made biodegradable. p(ATX) has previously shown to have antimicrobial properties in vitro, including inhibition of biofilm formation of S. epidermidis 1457, S. aureus MRSA252 and S. aureus MSSA476. In this work, we characterized the in vivo performance of p(ATX). Several in vivo evaluations were performed by implanting polyurethane catheter sections coated with pATXs in immunodeficient mice, followed by infection with S. aureus ATCC 6538. The polymer's capacity to inhibit bacterial biofilm formation on catheters was assessed. Two insights were generated. First, pATX has the capacity to significantly reduce the bacterial burden on coated catheters compared to uncoated catheters. Second, control over the biodegradation rate of the pATX, achieved via the use of hydrophilic diacid-comonomers, is required to maintain antimicrobial properties for at least 96 h. We found that slower degrading polymer is more beneficial in reducing bacterial load compared to rapidly degrading polymers, which begin to degrade immediately once hydrated. Thus, pATX, when appropriately designed, has the potential to perform as an antimicrobial coating for medical devices.

Attenuation of intestinal inflammation of polysaccharides from the seeds ofPlantago asiaticaL. as affected by ultrasonication

Ultrasound treatment was applied to modify the physicochemical properties of polysaccharides from the seeds of Plantago asiatica L. The initial polysaccharides concentration of 10 mg/mL, ultrasonic power of 800 W, and different treatment time (15 s, 30 s, 1 min, 2 min) were used. After irradiation, the average molecular weight (Mw) and polydispersity index of relative molecular mass (PID) of polysaccharides decreased. The apparent viscosity of degraded polysaccharides dropped compared with native polysaccharides. By using dextran sodium sulphate (DSS) colitis mouse model, enhanced intestinal anti‐inflammatory activity of degraded polysaccharides was proved by a significant reduction in the degree of neutrophil infiltration, indicated by decreased macrophage inflammatory protein‐2 secretion, and levels of inflammatory cytokines (TNF‐α and IL‐4) in inflamed colon. These results suggested that ultrasound treatment is a viable modification technology for high Mw polymer materials with high anti‐inflammatory activity. PRACTICAL APPLICATIONS: Ulcerative colitis (UC) is a chronic and nonspecific inflammatory disorder of the colonic mucosa, and assumed to be an autoimmune disease. PLCP was found to be one of the active ingredients responsible for many of the observed bioactivities including anti‐inflammation, anticomplement and facilitating defecation. However, it's extremely complex structure with high molecular weights and high viscosity hampered its applications. In this study, ultrasound irradiation was used to depolymerize PLCP, and its attenuation of intestinal inflammation was also studied.

Disclosing diversity of exopolysaccharide-producing lactobacilli from Spanish natural ciders

Lactic acid bacteria (LAB) are naturally occurring bacterial populations in traditional cider from the Basque Country (Spain), which is spontaneously fermented without starters. Some LAB are able to produce exopolysaccharides (EPS) thus causing viscosity, a cider spoilage called “ropiness” or “oilness”. A total of 41 isolates recovered between 1992 and 2009 from ropy ciders of different cider factories were included in the present study. Identification by 16S rRNA gene sequencing, biochemical traits (API), RAPD-PCR using four universal primers (M13, M13V, P1 and P2) and 16S-23S ISRs amplification profiles revealed that the spoiler species were L. collinoides, L. diolivorans, L. sicerae and L. suebicus. EPS production in L. collinoides and L. sicerae strains approached by PCR amplification of eps genes encoding for homopolysaccharide and heteropolysaccharide revealed that these strains synthesize heteropolysacccharides and in addition, L. collinoides CUPV231 synthesizes a 2-branched (1,3)-β-D-glucan. The molecular weight of their EPS determined by HP-SEC revealed the presence of three polymers with average molecular weights (MW) of around 106 g/mol, 104 g/mol and 103 g/mol. The middle-weight fraction was the most abundant except in L. sicerae CUPV261 which mainly produced the high Mw polymer.

Concepts in Cleanup of Fracturing Fluids Used in Conventional Reservoirs: A Literature Review

Summary Fracturing fluids are used for transport and placement of proppants in hydraulic-fracturing operations. In the case of conventional reservoirs, sufficient fluid viscosity is needed to transport proppant. An ideal fracturing fluid should possess enough viscosity to suspend and carry proppant. After the proppant placement, the fluid viscosity should drop to facilitate an efficient and quick fracture cleanup. This ensures adequate fracture conductivity. Most of the fracturing fluids used in these operations are dependent on crosslinking reactions between polymers and crosslinkers. Breaker technologies such as oxidizers, enzymes, fluoride compounds, oxides, vitamins, and decrosslinking agents are used to break the crosslinked polymer-based gels. These materials are added as components of the initial fracturing-fluids recipe. This paper will focus on the available breaker technologies used for degrading and cleaning up fracturing fluids used for conventional reservoirs. Each breaker has its own operating mechanism and window of application in terms of temperature and pH. The design and selection of a breaker package will first require an understanding of how the fracturing fluid forms. The current review reveals the crosslinking mechanisms of various fracturing fluids. These include the crosslinking of biopolymers with borates, the crosslinking of synthetic and biopolymers with metals, and the crosslinking of phosphate esters with metals. In the acidizing of carbonate reservoirs, the use of viscous fluids is needed to allow diversion of acid to lower-permeability paths. Moreover, the high viscosity retards the reaction between the acid and the rock, and this ensures deep penetration of the stimulation fluid. In this application, the viscosity develops as a response to the change in pH. Hydrocarbon fluids are used for hydraulically fracturing water-sensitive formations. Each of the aforementioned fracturing fluids has its own suitable breaker technology. For borate-crosslinked biopolymer gels, breakers such as oxidative and enzyme breakers can be used to reduce fluid viscosity by degrading polymer chains. An alternative approach to reduce viscosity of this type of fluid is the use of acids that lower the pH and decrosslink the fluid. A third route to reduce this fluid viscosity is by use of chelating agents and complexing agents. Lowering fluid viscosity alone may not sufficiently guarantee adequate proppant-pack and formation cleanup. It has been proved that low-viscosity fluids may still contain high-molecular-weight (MW) polymers that could severely damage formation and proppant pack. These high-MW polymers should be further broken into low-MW fragments with oxidizers or enzymes to achieve better production numbers. When metals are used to crosslink biopolymers and synthetic polymers, breakers such as oxidative breakers can still be effective. Acid fracturing fluids use fluoride-based breakers that can complex with the zirconium (Zr) and hence decrosslink the gel. When fracturing high-temperature wells, breakers can prematurely degrade the gel viscosity. This leads to less proppant placement and possibly screens out the proppant. As a result, the propped fracture becomes shorter and the well productivity will be less. To avoid this, breakers are encapsulated with materials that act as barriers between the breaker and fluid. The dissolution of the encapsulating material gives additional time for the gel to place the proppant. This paper reviews more than 100 papers and patents to summarize the experience and available knowledge in the area of using breakers for cleaning up fracturing fluids.

Synergistically enhanced stability of laccase immobilized on synthesized silver nanoparticles with water-soluble polymers

Silver nanoparticles (AgNPs) were synthesized by citrate reduction method in the presence of polymers, poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA) and chitosan, used as stabilizing agents, and an oxidoreductase enzyme, laccase (Lac), with the goal of expanding the NPs antimicrobial action.AgNPs were characterized by UV–vis spectrometry, dynamic light scattering and transmission electron microscopy. As protecting agents, PEG and PVA promoted the formation of spherical uniformly-shaped, small-sized, monodispersed AgNPs (≈20nm). High Mw polymers were established as most effective in producing small-sized NPs. Chitosan's viscosity led to the formation of aggregates. Despite the decrease in Lac activity registered for the hybrid formulation, AgNPs-polymer-Lac, a significant augment in stability over time (up to 13days, at 50°C) was observed. This novel formulation displays improved synergistic performance over AgNPs-Lac or polymer-Lac conjugates, since in the former the Lac activity becomes residual at the end of 3days. By enabling many ionic interactions, chitosan restricted the mass transfer between Lac and substrate and, thus, inhibited the enzymatic activity.These hybrid nanocomposites made up of inorganic NPs, organic polymers and immobilized antimicrobial oxidoreductive enzymes represent a new class of materials with improved synergistic performance. Moreover, the Lac and the AgNPs different antimicrobial action, both in time and mechanism, may also constitute a new alternative to reduce the probability of developing resistance-associated mutations.

Poly(ethylene glycol) modified poly(2-hydroxypropylene imine) as efficient reagent for siRNA transfection

MPEG’ylated poly(2-hydroxypropylene imines) were synthesised using 1,3-diamino-2-propanol, 1,3-dibromo-2-propanol and methoxy poly(ethylene glycol) (MPEG, Mn 1000, 2000, 5000). Trying to find conditions favourable for attachment of MPEG chains, MPEG iodide was either added to the initial mixture of the monomers (method A), or was introduced later, at the end of the reaction (method B). MPEG’ylated derivatives of PHPI were characterized by FTIR and NMR spectroscopy, SEC, DLS, DSC and potentiometric titration and were tested for DNA and siRNA delivery in vitro. Efficiency of high MW / low MPEG content PHPI derivatives in DNA transfection was similar to that of PHPI. MPEG grafting had a positive effect on siRNA delivery: high MW polymers with low content of MPEG performed significantly better than non-MPEG’ylated PHPI and low-molecular-weight polymers with high content of MPEG. The length of MPEG chains attached to the polymers had no effect over the transfection efficiency.

Effect of internal electron donor on the active center distribution in MgCl2-supported Ziegler–Natta catalyst

1-Hexene polymerizations catalyzed by three kinds of MgCl2-supported Ziegler–Natta catalysts respectively, in which Cat-1 contains no internal donor (ID), Cat-2 contains diethylphthalate as ID, and Cat-3 contains anisole as ID, were quenched by cinnamoyl chloride to label the propagation chains. The effects of ID on active centers (C⁎) distribution and reactivity of different C⁎ were studied. Diethylphthalate significantly reduced the number of all kinds of C⁎, with those producing medium to high Mw polymer which were reduced more. Anisole significantly reduced the number of C⁎ producing medium to high Mw polymer, but slightly affected those producing low Mw polymer. Both IDs greatly enhanced the reactivity of C⁎ in the medium to high Mw fractions, while they slightly changed the properties of C⁎ producing low Mw polymer. Possible mechanisms of these ID effects are discussed.

Solid/Hollow Depots for Drug Delivery, Part 1: Effect of Drug Characteristics and Polymer Molecular Weight on the Phase-Inversion Dynamics, Depot Morphology, and Drug Release

The objective of this research was to evaluate the effect of drug characteristics and polymer molecular weight (MW) on phase-inversion dynamics, depot morphology, and drug release in injectable in situ depot-forming drug delivery systems. Two poly(lactide-co-glycolide) (50:50) polymers with different MW (RG502 and RG504) and two drugs with different hydrophilicity (metoclopramide salt and metoclopramide base) were studied here. The drug release from injectable depots, the polymer MW changes, and the cross-sectional depot morphologies were investigated, respectively. The results show that the initial drug release from high-MW polymer RG504 was always faster than that from low-MW polymer RG502, regardless of the drug type. Interestingly, depot morphology shows the development of a hollow core for RG502, whereas RG504 forms a solid core. The relationship of the depot morphology to release kinetics is proposed based on these observations. The use of basic drug catalyzes polymer degradation, during processing and over time. These affect starting MW and subsequent MW, and the effect on release kinetics is consistent with the general effects of MW. This research suggests that the polymer MW is an important effect on the polymer phase inversion kinetics, and thus the resultant depot morphology.

HIGH TEMPERATURE ELUTION PEAKS IN TEMPERATURE RISING ELUTION FRACTIONATION (TREF): THE BEHAVIOR OF HIGH MOLECULAR WEIGHT SPECIES

The effects of low molecular weight species in the analytical TREF (A-TREF) have been reported. Remarkably, no literature report, describes or even mentions, possible effects of high MW polymers on the TREF mechanism. The appearance of high temperature peaks in TREF elution has been experimentally linked to the presence of high molecular weight species in the case of high density (i.e., unbranched) polyethylene. Baseline resolved peaks or shoulders on the main peak (which main peak is presumably due to lower molecular weight fraction species) were observed with peak maxima as much as ∼10–25°C higher than baseline return of the high temperature side of the main peak. These high temperature peaks are apparently due to high molecular weight species, which undergo delayed dissolution, after melting in the presence of the diluent. These transiently “undissolved” species apparently cause irreproducible A-TREF elution curves, resulting in peaks moving along the temperature axis. These high temperature peaks were observed for a polymer having a highest molecular weight fraction of species with about 10 million molecular weight, but were not observed for another polymer having a highest molecular weight fraction of species with about 1 million molecular weight.

Effect of molecular weight on the efficiency of poly(N-vinylcarbazole)-based polymer light-emitting diodes

Polymer light-emitting diodes based on poly(N-vinylcarbazole) (PVK) with molecular weights MW of 1.1 × 106 and ∼7.5 × 104 are compared. For devices without an electron transport layer (ETL), the high MW PVK yields higher external quantum efficiency (0.67% vs 0.18%), but for devices with an ETL, the low MW PVK yields higher efficiency (1.13% vs 0.83%). This intriguing difference is believed to result from higher energetic disorder in the high MW polymer and different recombination zone-quenching metal electrode distances, in agreement with Konezny et al. [Appl. Phys. Lett. 97, 143305 (2010)].

Chemical characterization of polymerized products formed in the reactions of matairesinol and pinoresinol with the stable radical 2,2-diphenyl-1-picrylhydrazyl

AbstractPolymerization reactions of the lignans matairesinol and pinoresinol with the stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) were studied. The reactions were rapid and almost quantitative. The molecular weight distribution (MWD) of the formed lignan dimers and polymers was determined by high-performance size-exclusion chromatography (HPSEC) combined with evaporative light-scattering detection (ELSD), and the compounds were characterized by HPLC-MS, pyrolysis-GC/MS, NMR, MALDI-ToF-MS, and GC-MS of the monomeric and dimeric units formed by KMnO4oxidation. The yield of high-MW polymers is higher for pinoresinol (69%) than for matairesinol (43%). According to the HPSEC-ELSD analyses, the MWD is also broader for the pinoresinol polymers. The latter seem to consist mainly of hepta-hexacontalignans (MW 2.5–21.4 kDa), whereas the matairesinol polymers are mainly penta-pentadecalignans (MW 1.8–5.3 kDa). The polymers seem to contain mainly unmodified lignan units linked by 5-5′ bonds.

Fabrication of 3D interconnected porousTiO2 nanotubes templatedby poly(vinyl chloride-g-4-vinyl pyridine) for dye-sensitized solar cells

Porous TiO2 nanotube arrays with three-dimensional (3D) interconnectivity wereprepared using a sol–gel process assisted by poly(vinyl chloride-graft-4-vinylpyridine), PVC-g-P4VP graft copolymer and a ZnO nanorod template. A7 µm long ZnO nanorod array was grown from the fluorine-doped tinoxide (FTO) glass via a liquid phase deposition method. TheTiO2 sol–gel solutiontemplated by the PVC-g-P4VP graft copolymer produced a random 3D interconnection betweenthe adjacent ZnO nanorods during spin coating. Upon etching of ZnO,TiO2 nanotubes consisting of 10–15 nm nanoparticles were generated, as confirmed by wide-anglex-ray scattering (WAXS), energy-filtering transmission electron microscopy (EF-TEM) andfield-emission scanning electron microscopy (FE-SEM). The ordered and interconnectednanotube architecture showed an enhanced light scattering effect and increased penetrationof polymer electrolytes in dye-sensitized solar cells (DSSC). The energy conversionefficiency reached 1.82% for liquid electrolyte, and 1.46% for low molecular weight(Mw) and 0.74%for high Mw polymer electrolytes.

Furan-based Polysemiacylcarbazides by Polyaddition of Bis(furanic hydrazide)s with Diisocyanates

A solution polyaddition procedure was applied to prepare furanic polyacylsemicarbazides based on 2,2′-isopropylidene-bis(5-(2-furoyl) hydrazide) and aliphatic or aromatic diisocyanates. Model compounds were prepared to facilitate the synthesis and the characterization of the polymers. A systematic study of reaction parameters (the nature of the organic phase, the temperature, the reaction time, and the concentration of monomers) was carried out. High MW polymers were obtained after 12 h reaction at 20°C with 0.2 M monomer solutions in dimethylacetamide. In fact, the polyacylsemicarbazides obtained had inherent viscosities ranging from 0.63 to 0.85 dL/g. There showed good solubility in aprotic polar solvents. The 1H and 13C-NMR spectra were consistent with the expected structures. These furan-based polyacylsemicarbazides are thermally stable up to 290°C, but exhibit a complex thermal behavior. This was explained by the cyclohydration of acylsemicarbazide groups into NH-substituted oxadiazoles, resulting in rigid and high melting polymers, less stable, however, than conventional aromatic polyoxadiazoles.

Preparation of TiO2 spheres with hierarchical pores via grafting polymerization and sol–gel process for dye-sensitized solar cells

Titania (TiO2) nanoparticles were surface-modified via atom transfer radical polymerization (ATRP) with hydrophilic poly(oxyethylene) methacrylate (POEM), which can coordinate to the TiO2 precursor, titanium(IV) isopropoxide (TTIP). Following application of a sol–gel process and calcination at 450 °C, TiO2 nanospheres with hierarchical pores were generated, as confirmed by the shifting of conduction bands in TiO2 using UV-visible spectroscopy and X-ray photoelectron spectroscopy (XPS). The particle size and morphology of TiO2 were characterized using wide angle X-ray scattering (WAXS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Brunauer–Emmett–Teller (BET) analysis revealed bimodal distribution of TiO2 pore sizes with peaks at 6 nm and 50 nm to afford better penetration of polymer electrolyte, as confirmed by electrochemical impedance spectroscopy (EIS). Dye-sensitized solar cells (DSSC) made from TiO2 nanospheres with hierarchical pores exhibited improved photovoltaic efficiency (3.3% for low molecular weight (Mw) and 2.5% for high Mw polymer electrolytes), as compared to those from neat TiO2 nanoparticles (2.4% for low Mw and 1.3% for high Mw) at 100 mW/cm2, owing to the increased surface areas and light scattering.