Surface and adhesion properties of poly(imide-siloxane) block copolymers

Poly(imide-siloxane) (PIS) block copolymers were studied with respect to their structure surface and adhesive properties relationship. The study of the morphology of PIS copolymers characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Atomic Force Microscopy (AFM) shows a growth of the surface roughness by increase of the content of siloxane. With an increase of siloxane content Attenuated Total Reflection-Fourier Transform Infra Red (ATR-FTIR) spectroscopy detected a growth of the absorption bands near 1100 cm⁻¹ characteristic for siloxane group, and a decrease at 1700-1800 cm⁻¹ corresponding to carbonyl groups of polyimide moieties. The X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight-Secondary Ion Mass Spectroscopy (TOF-SIMS) analysis showed an excessive increase of Si on surface of the copolymer. The relatively small amount of siloxane in PIS block copolymer, 10-20 wt.%, increased significantly the contact angle of water due to the surface hydrophobization of the copolymer and the significant decrease of the surface energy of the PIS copolymer has been observed. The polar component of surface energy shows an intense decrease, whereas its dispersive component increases. The increase of the surface hydrophobicity reduced the peel as well as shear strengths of epoxy adhesive joints. The relationship between peel strength of adhesive joint to epoxy and polar fraction of PIS copolymer can be described by exponential decay dependence.     

Bacterial polyesters grafted with poly(ethylene glycol): Behaviour in aqueous media

An easy method for grafting of poly(3-hydroxyoctanoate-co-3-hydroxyundecenoate) (PHOU) was developed. Oxidation of the pendant double bonds of PHOU into carboxyl groups to yield poly(3-hydroxyoctanoate-co-3-hydroxy-9-carboxydecanoate) (PHOD) and the esterification of the carboxyl side groups with poly(ethylene glycol) (PEG) were carried out in a single reaction solution. The grafting yield is dependent on the molar mass of the PEG graft. The maximum carboxyl group conversion (52%) was obtained with PEG M_n = 350 and decreased with increasing molar mass of PEG (19% for PEG M_n = 2000). Yields were determined by ¹H and ¹³C NMR. Short PEG grafts lowered the glass transition temperature (PHOD-g-PEG 350 −57 °C) compared to PHOD (−19 °C) and PHOU (−39 °C). This effect depends on the COOH conversion and PEG chain length. Grafting enhanced the hydrophilic character of the modified polymers making them soluble in polar solvents, such as alcohols and water/acetone mixtures. PHOD-g-PEG films were more stable towards hydrolytic degradation as PHOD films. No obvious modification of films was observed after more than 200 days at pH 7.2 and 37 °C. The molar mass of the grafted polymers decreased only slightly during this period, while PHOD films were hydrolyzed into soluble fragments.     

Glass transition of thin films of poly(2-vinyl pyridine) and poly(methyl methacrylate): nanocalorimetry measurements

Glass transitions were observed in thin films of poly(2-vinyl pyridine) (P2VP) and poly(methyl methacrylate) (PMMA) using a scanning nanocalorimetry technique which has both high sensitivity (10⁻⁹ J/K) and high scan rates (10⁴-10⁵ K/s). Samples were deposited by the spin-cast method. The thickness of samples was 100-400 nm. Glass transition temperature, obtained by nanocalorimetry, is shifted toward higher temperatures by 10-20 K and activation enthalpy of glass transition is shifted to lower values by factor of 2-4. The glass transition characteristics of both polymers are discussed in terms of the standard Tool-Narayanaswamy-Moynihan (TNM) multi-parameter model.     

Thermal oxidation of metallocene ethylene-1-olefin copolymer films during one year oven aging

Metallocene ethylene homopolymer, ethylene-1-hexene and ethylene-1-octadecene copolymer films were characterized and analysed during their aging in a forced draft oven at 60 °C and compared to commercial polymers (HDPE and LDPE). Each polymer is essentially different in its structure, and the variables used in the present study are comonomer size and content in the main linear backbone polymer. The polymers were characterized initially using GPC, DSC, FTIR, and tensile tests. Later, at different time intervals, samples were removed from the oven and characterized using FTIR and GPC in order to detect changes in chemical structure, size, and molecular weight distribution due to thermo-oxidative aging. At the end of aging, films were subjected to tensile tests to quantify the effect of time on their useful life. As a qualitative reference parameter, the carbonyl index, the ratio of the infrared absorbance of the CO stretching band at 1715 cm⁻¹ and the absorbance of a reference band at 718 cm⁻¹, was determined. Kinetic thermo-oxidation is related to comonomer size and content in the main backbone polymer. As comonomer size decreases or comonomer content increases, degradation rate increases. The scission factor (S) and carbonyl index (CI) graphs of each material show a slope increase which is related to the autocatalytic rate of oxidation.     

High glass transitions of novel organosoluble polyamide-imides based on noncoplanar and rigid diimide-dicarboxylic acid

A series of novel polyamide-imides (PAIs) with high glass transition temperature were prepared from diimide-dicarboxylic acid, 2,2′-bis(trifluoromethyl)-4,4′-bis(trimellitimidophenyl)biphenyl (BTFTB), by direct polycondensation with various diamines in N-methyl-2-pyrrolidinone using triphenyl phosphite and pyridine as condensing agents in the presence of dehydrating agent (CaCl₂). The yield of the polymers was obtained was high with moderate to high inherent viscosities (0.80-1.03 dL g⁻¹). Gel permeation chromatography (GPC) of the polymers showed number-average and weight-average molecular weights up to 8.6 × 10⁴ and 22 × 10⁴, respectively. The PAIs were amorphous in nature. Most of the polymers exhibited good solubility in various solvents such as N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), pyridine, cyclohexanone and tetrahydrofuran. The polymer films had tensile strength in the range of 79-103 MPa, an elongation at break in the range of 6-16%, and a tensile modulus in the range between 2.1 and 2.8 GPa. The glass transition temperatures of the polymers were determined by DMA method and they were in the range of 264-291 °C. The coefficients of thermal expansion (CTE) of PAIs were determined by TMA instrument and they were between 29 and 67 ppm °C⁻¹. These polymers were fairly thermally stable up to or above 438 °C, and lose 10% weight in the range of 446-505 °C and 438-496 °C, respectively, in nitrogen and air. These polymers had exhibited 80% transmission wavelengths which were in the range of 484-516 nm and their cutoff wavelengths were in between 418 and 434 nm. The PAIs with trifluoromethyl group have higher bulk density resulting in higher free volume and then lowering the dielectric constant.     

Preparation and characterization of poly(imide siloxane) (PIS)/titania(TiO2) hybrid nanocomposites by sol-gel processes

Poly(imide siloxane)(PIS)/titania(TiO₂) hybrid nanocomposites with organic-inorganic covalent bonding have been successfully synthesized by sol-gel processes. The PIS copolymer synthesized in this study was characterized by the observed coexisting two segments: the polyimide (PI) segment and polydimethyldiphenylsiloxane segment, and the latter were specially featured with the introduction of a diphenyl group for improved homogeneity.The obtained TiO₂ networks in PIS matrix were well dispersed and their average diameter was less than 50 nm. Meanwhile, the PIS/TiO₂ hybrid nanocomposite films exhibited good optical transparency at 20 wt% of TiO₂ content. The thermal stability, tensile strength and elongation of the nanocomposites decreased with increasing TiO₂ content. The glass transition temperature (T_g) and Young’s modulus increased with increasing TiO₂ content. The chemical structure and morphologies of PIS/TiO₂ hybrid nanocomposites was characterized by Fourier transform infrared spectroscope (FT-IR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM). The T_g and thermal stability were measured by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), respectively. The mechanical properties were examined by dynamic mechanical analysis (DMA) under controlled force mode.     

Selective preconcentration and determination of iodine species in milk samples using polymer inclusion sorbent

A method to determine low levels of iodine species namely I⁻ and IO₃⁻ in aqueous samples was developed and applied to milk and milk powder samples. It is based on selective preconcentration of I⁻ in polymer inclusion sorbent (PIS) and neutron activation analysis (NAA) of I⁻ sorbed in PIS. The PIS was found to be highly selective for I⁻ in presence of IO₃⁻ and other anions commonly present in the milk samples. In order to preconcentrate total I⁻ + IO₃⁻ content in the PIS, IO₃⁻ was reduced to I⁻ using a mixture of acetic acid and ascorbic acid. It was found that total iodine content in milk could be determined with epithermal neutron activation analysis (ENAA). A scheme was developed to determine I⁻, IO₃⁻ and total iodine. The developed method was applied to milk reference materials (NIST SRM-1549 and IAEA-RM-153 milk powder) and a commercially available milk powder. The scheme for estimation of iodine in different forms was validated by using reference material NIST SRM-1549.     

Electrosyntheses of high quality poly(5-methylindole) films in mixed electrolytes of boron trifluoride diethyl etherate and diethyl ether

High quality poly(5-methylindole) (P5MeI) films, especially with good fluorescence properties, were synthesized electrochemically by direct anodic oxidation of 5-methylindole in boron trifluoride diethyl etherate (BFEE) containing additional 50% diethyl ether (EE) (by volume). The oxidation potential onset of 5-methylindole in this medium was measured to be only 0.84 V vs. SCE, which was much lower than that determined in acetonitrile + 0.1 mol L⁻¹ TBATFB (1.08 V vs. SCE). P5MeI films obtained from this medium showed good electrochemical behavior and good thermal stability with conductivity of 10⁻² S cm⁻¹, indicating that BFEE was a better medium than acetonitrile for the electrosyntheses of P5MeI films. Dedoped P5MeI films were thoroughly soluble in strong polar solvent such as dimethyl sulfoxide (DMSO). ¹H NMR spectroscopy and FT infrared spectrum of dedoped P5MeI films strongly suggested that the monomers were linked via the positions 2 and 3. Fluorescent spectral studies indicated that P5MeI was a good violet-blue light emitter with the excitation and emission wavelength of 310 nm and 418 nm, respectively. To the best of our knowledge, this is the first case that 5-methyl group substituted polyindole films with good fluorescence properties can be electrodeposited.     

Novel dihydrazone based polymers for electrophotography

The novel family of hole-transporting polymers containing hydrazone moieties is reported. The polymers were prepared in polyaddition reaction of dihydrazone-containing diepoxides with bifunctional nucleophilic linking agents in the presence of catalyst triethylamine. Obtained polymers were found to constitute novel polymeric hole transporting materials characterized by differential scanning calorimetry and time of flight method. The highest hole drift mobility in the newly synthesized polymers exceed 10⁻⁵ cm² V⁻¹ s⁻¹ at an electric field of 10⁶ V cm⁻¹.     

Self-organization of dipeptide-grafted polymeric nanoparticles film: A novel method for surface modification

Novel dipeptide-grafted polymeric nanoparticles were prepared by grafting the dipeptide (Gly-Gly) to a block copolymer backbone, comprised of styrene-alt-(maleic anhydride) and styrene. In aqueous solution PSt₁₃₀-b-P(St-alt-MAn)₅₈-g-GlyGly₂₆ formed stable dispersed spherical aggregates of ca. 75 nm. The critical micelle concentration for the dipeptide-grafted block copolymer self-aggregates was 6.3 × 10⁻³ mg mL⁻¹. The zeta-potential of the aggregates was estimated experimentally. The dispersed polymer nanoparticles effectively self-organized to form stable nanoparticle thin films on hydrophobic solid surfaces, such as octadecyltrichlorosilane modified glass (OTS-G). As the ionic strength and temperature of the polymer suspension increased the surface coverage of the nanoparticle film increased and its hydrophobicity (water contact angle) decreased. Significantly less bovine serum albumin (BSA) adsorbed to nanoparticles modified surfaces with compared OTS-G surfaces. Diglycine grafted polymer nanoparticles have the potential to be used as a novel platform to study protein-protein interactions and to control fouling.     

Sulfide and sulfoxide based poly(ether-amide)s: Synthesis and characterization

Two new diacid monomers, 2,2′-sulfide bis(4-methyl phenoxy acetic acid) and 2,2′-sulfoxide bis(4-methyl phenoxy acetic acid) were successfully synthesized by refluxing the 2,2′-sulfide bis(4-methyl phenol) and 2,2′-sulfoxide bis(4-methyl phenol) with chloroacetonitrile in the presence of potassium carbonate, and subsequent basic reduction. Two novel series of poly(sulfide-ether-amide)s and poly(sulfoxide-ether-amide)s with aliphatic units in the main chain were prepared from diacids with various diamines.The polyamides were obtained in quantitative yields and their inherent viscosities were in the range of 0.43-0.89 dl g⁻¹ at a concentration of 0.5 g dl⁻¹ in N,N-dimethylacetamide (DMAc) solvent at 25 °C. They showed good thermal stability. The temperature for 10% weight loss in argon atmosphere was in the range of 350-415 °C. The polymers showed glass transition temperatures between 228 and 261 °C. Almost all of the polyamides were readily soluble in a variety of polar solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO).     

Synthesis, characterization and biocompatibility studies of oligosiloxane modified polythiophenes

This paper describes the preparation and characterization of homopolymers of 3-oligo(dimethylsiloxane)thiophene macromonomers, V-VIII, and copolymers with 3-methylthiophene. The thiophene macromonomers were prepared by hydrosilylation reaction between ω-(Si-H)-oligo(dimethylsiloxane), I-IV, and 3-propenylthiophene using a platinum-divinyltetramethyldisiloxane complex as the catalyst. The products were characterized by ¹H, ¹³C, ²⁹Si NMR and IR spectroscopy; DSC (differential scanning calorimetry) and GPC studies. Two distinct glass transition temperatures are observed for poly[VIII], a T_g at −79 °C corresponds to the soft oligo(dimethylsiloxane) phase and the T_g at 190 °C corresponds to the hard thiophene backbone. Homopolymers of V and VI, and copolymers may be doped with I₂ to generate electronic conductive material, a copolymer of poly[V]-co-poly[3-methylthiophene] (50/50, w/w) has an electronic conductivity value of 5 × 10⁻⁵ S/cm at 25 °C. The polymers are tractable and may be molded into thin films; a number of the polymers are soluble in organic solvents. Polythiophene modified with oligosilioxanes are biocompatibile; the polymers minimally interfere with the growth of HeLa cells.     

Investigation of homopolymerization rate of perfluoro-4,5-substituted-2-methylene-1,3-dioxolane derivatives and properties of the polymers

Five perfluoro-4,5-substituted-2-methylene-1,3-dioxolane monomers were synthesized. These monomers were found to readily polymerized by a free radical initiator in bulk and/or in solutions. Homopolymerization rates were determined using in situ ¹⁹F NMR measurements and found to be 0.25 to 1.66 × 10⁻⁴ mol L⁻¹ s⁻¹ in 1,1,2-trichlorotrifluoroethane at 41 °C using the perfluorodibenzoyl peroxide as an initiator. The rates depend on the substituents on the 4 and 5 positions of the dioxolane. The purified polymers were thermally stable (up to 350 °C). They show low refractive indexes (1.33-1.36 at 532 nm). They are transparent from UV to near IR region and have high glass transition temperatures (100-170 °C).     

Facile synthesis of PbTe nanoparticles and thin films in alkaline aqueous solution at room temperature

A novel, simple, and cost-effective route to PbTe nanoparticles and films is reported in this paper. The PbTe nanoparticles and films are fabricated by a chemical bath method, at room temperature and ambient pressure, using conventional chemicals as starting materials. The average grain size of the nanoparticles collected at the bottom of the bath is ∼25 nm. The film deposited on glass substrate is dense, smooth, and uniform with silver gray metallic luster. The film exhibits p-type conduction and has a moderate Seebeck coefficient value (∼147 μV K⁻¹) and low electrical conductivity (∼0.017 S cm⁻¹). The formation mechanism of the PbTe nanoparticles and films is proposed.     

Development of hydrogen peroxide biosensor based on in situ covalent immobilization of horseradish peroxidase by one-pot polysaccharide-incorporated sol-gel process

A simple and reliable one-pot approach was established for the development of a novel hydrogen peroxide (H₂O₂) biosensor based on in situ covalent immobilization of horseradish peroxidase (HRP) into biocompatible material through polysaccharide-incorporated sol-gel process. Siloxane with epoxide ring and trimethoxy anchor groups was applied as the bifunctional cross-linker and the inorganic resource for organic-inorganic hybridization. The reactivity between amine groups and epoxy groups allowed the covalent incorporation of HRP and the functional biopolymer, chitosan (CS) into the inorganic polysiloxane network. Some experimental variables, such as mass ratio of siloxane to CS, pH of measuring solution and applied potential for detection were optimized. HRP covalently immobilized in the hybrid matrix possessed high electrocatalytic activity to H₂O₂ and provided a fast amperometric response. The linear response of the as-prepared biosensor for the determination of H₂O₂ ranged from 2.0 × 10⁻⁷ to 4.6 × 10⁻⁵ mol l⁻¹ with a detection limit of 8.1 × 10⁻⁸ mol l⁻¹. The apparent Michaelis-Menten constant was determined to be 45.18 μmol l⁻¹. Performance of the biosensor was also evaluated with respect to possible interferences. The fabricated biosensor exhibited high reproducibility and storage stability. The ease of the one-pot covalent immobilization and the biocompatible hybrid matrix serve as a versatile platform for enzyme immobilization and biosensor fabricating.     

Fluorescence single-molecule counting assays for protein quantification using epi-fluorescence microscopy with quantum dots labeling

A single-molecule counting approach for quantifying the antibody affixed to a surface using quantum dots and epi-fluorescence microscopy is presented. Modifying the glass substrates with carboxyl groups provides a hydrophilic surface that reacts with amine groups of an antibody to allow covalent immobilization of the antibody. Nonspecific adsorption of single molecules on the modified surfaces was first investigated. Then, quantum dots were employed to form complexes with surface-immobilized antibody molecules and used as fluorescent probes for single-molecule imaging. Epi-fluorescence microscopy was chosen as the tool for single-molecule fluorescence detection here. The generated fluorescence signals were taken by an electron multiplying charge-coupled device and were found to be proportional to the sample concentrations. Under optimal conditions, a linear response range of 5.0 × 10⁻¹⁴-3.0 × 10⁻¹² mol L⁻¹ was obtained between the number of single molecules and sample concentration via a single-molecule counting approach.     

Synthesis of novel crosslinked sulfonated poly(ether sulfone)s using bisazide and their properties for fuel cell application

Novel crosslinked sulfonated poly(ether sulfone)s (PESs) were prepared by thermal irradiation of the allyl-terminated telechelic sulfone polymers using a bisazide. The sulfonated polymers in different comonomer compositions were fully characterized by ¹H NMR, and the crosslinked structure was also verified by FT-IR spectroscopic analyses. Having both the uniform distribution of the hydrophilic conductive sites and controlled hydrophobic nature by minimized crosslinking over the rigid rod poly(ether sulfone) backbone, the crosslinked polymer membrane (PES-60) offered excellent proton conductivity of 0.79 S cm⁻¹ at 100 °C together with hydrolytic and oxidative stability. In addition, only 17% of methanol permeability of the Nafion^® was observed for the crosslinked PES-60.     

Hole-transporting [3,3′]bicarbazolyl-based polymers and well-defined model compounds

Polymers containing bicarbazolyl moieties in the main chain have been synthesized by the modified Ullmann coupling reaction from 9H,9′H-[3,3′]bicarbazolyl and different dihalo derivatives. The number-average molecular weights of the polymers synthesized were in the range of 2500-6200 with a molecular weight distribution of 1.6-3.1. Well-defined model compounds for the polymers have been synthesized by stepwise reactions. All these compounds have been found to form glasses with glass transition temperatures in the range of 57-119 °C as characterised by differential scanning calorimetry. The electron photoemission spectra of the compounds have been recorded and the ionisation potentials of 5.35-5.4 eV have been established. Room temperature hole drift mobility of the synthesized compounds molecularly dispersed in a polymer host range from 10⁻⁶ to 3 × 10⁻⁵ cm²/V s at an electric field of 10⁶ V/cm at the room temperature.     

Synthesis and properties of polyoxyarylenesiloxanes

High molecular weight polymers containing oligosiloxanes in the backbone were made by the reaction of aromatic diols with α,ω-diaminosiloxane homologs. The glass transition temperatures dropped by 30–40°C in a homologous series with each siloxane added. The thermal stability also suffered when increasing the number of siloxane groups. The polymers all displayed high % char measurements and one polymer (disiloxane) tested had a V₀ rating by UL-94 testing. The trisiloxane-containing polymer had a high percent elongation at break (>300%). All the polymers tested were fairly susceptible to hydrolysis. © 1994 John Wiley & Sons, Inc.     

Layer by layer assembly of catalase and amine-terminated ionic liquid onto titanium nitride nanoparticles modified glassy carbon electrode: Study of direct voltammetry and bioelectrocatalytic activity

A novel, simple and facile layer by layer (LBL) approach is used for modification of glassy carbon (GC) electrode with multilayer of catalase and nanocomposite containing 1-(3-Aminopropyl)-3-methylimidazolium bromide (amine terminated ionic liquid (NH₂-IL)) and titanium nitride nanoparticles (TiNnp). First a thin layer of NH₂-IL is covalently attached to GC/TiNnp electrode using electro-oxidation method. Then, with alternative self assemble positively charged NH₂-IL and negatively charged catalase a sensitive H₂O₂ biosensor is constructed, whose response is directly correlated to the number of bilayers. The surface coverage of active catalase per bilayer, heterogeneous electron transfer rate constant (k_s) and Michaelis–Menten constant (K_M) of immobilized catalase were 3.32 × 10⁻¹² mol cm⁻², 5.28 s⁻¹ and 1.1 mM, respectively. The biosensor shows good stability, high reproducibility, long life-time, and fast amperometric response with the high sensitivity of 380 μA mM⁻¹ cm⁻² and low detection limit of 100 nM at concentration range up to 2.1 mM.