Structural determination of Torlon 4000T polyamide-imide by NMR spectroscopy

High field ¹H and ¹³C NMR spectroscopy and published information in the scientific literature were combined in the determination of the chemical structure of the commercially available Torlon^® 4000T, a polyamide-imide which is widely used in applications where good mechanical, thermal and oxidative properties are required. It was found from qualitative and quantitative NMR analysis that the three monomers used to synthesize Torlon are as follows: 1.0 trimellitic anhydride chloride, 0.7 4,4′-oxydianiline, 0.3 m-phenylenediamine. It was also shown that the sequence of appearance of the polymer's amide and imide functional groups follows a certain distribution of Amide-Imide, Amide-Amide and Imide-Imide repeat units due to the dual reactive sites, acid chloride and anhydride, of the monomer trimellitic anhydride chloride.     

Sequestration of electroactive materials in a high Tg, insulating polymer matrix for optoelectronic applications. Part 2. Photovoltaic devices

The incorporation of high levels of electroactive compounds into a high T_g matrix polymer was investigated in photovoltaic (PV) devices. The combination of electron donor-electron acceptor pairs with optionally light harvesting organics (e.g. laser dyes) in the high T_g polymer matrix yielded PV performance in the range of literature data typically reported for organic based PV devices. The advantages for using a high T_g matrix include increasing the T_g of the electroactive compounds, preventing crystallization, improving the mechanical properties of the active layer(s) and the ability to employ lower cost fabrication processes. While the basic concept has been demonstrated, further optimization would be required to achieve a useful combination of photovoltaic properties. As in the companion paper on utilization of a high T_g polymer to sequester low molecular weight electroactive species for LED devices, this paper demonstrates the same concept for PV devices. The approach to solve the issues with low molecular weight electroactive species noted in the literature to date often involves covalent bonding of these compounds to polymeric backbones. This and the companion paper well-illustrates the blend approach is equally viable and offers a much simpler methodology.     

Sequestration of electroactive materials in a high Tg, insulating polymer matrix for optoelectronic applications. Part 1. Light emitting diode devices

The use of a high T_g, insulating polymer to sequester low molecular weight electroactive materials at high addition levels for utility in LED devices has been demonstrated. The threshold for effective light emission appears to be in the range of 15 wt% electroactive compounds in agreement with the percolation theory of deGennes. The high T_g polymer allows for suppression or elimination of the undesired crystallization of the electroactive species and yields a significant increase in the T_g of the light emitting layer (also required). Additionally this approach offers the potential for easier (and lower cost) fabrication routes not generally employed for low molecular weight electroactive materials (e.g. spin coating, ink jet printing, roll-to-roll printing). The improved mechanical properties of the light emitting layer with high molecular weight polymer addition should allow for improved performance/durability in flexible displays. The simple blend approach should be an attractive alternative to other more common methods reported in the literature employing covalent bonding of electroactive species to polymeric backbones to achieve the same results. This approach also allows for multiple addition of dopants (e.g. laser dyes), hole transport materials and electron transport materials in a single light emitting layer. While these results demonstrate the concept, optimization was not conducted and significant improvements would be expected with proper adjustment of the many variables possible with this approach.     

Miscibility in blends of linear and branched poly(ethylene oxide) with methacrylate derivative random copolymers and estimation of segmental χ parameters

Miscibility in the blends of poly(ethylene oxide) (PEO) with n-hexyl methacrylate-methyl methacrylate random copolymers (HMA-MMA) and 2-ethylhexyl methacrylate-MMA random copolymers (EHMA-MMA) was evaluated using glass transition and light scattering methods. EHMA-MMA was more miscible with PEO than HMA-MMA. Both blends of PEO with HMA-MMA and EHMA-MMA showed UCST-type miscibility although homopolymer blends PEO/PMMA were predicted to be of LCST-type. This was attributed to an increase in the exchange enthalpy with increasing HMA or EHMA composition in the random copolymer. From the copolymer composition dependence of miscibility the segmental χ parameters of HMA/MMA, EHMA/MMA, EO/HMA and EO/EHMA were estimated using the Flory-Huggins theory extended to random copolymer systems. Miscibility in the blends of branched PEO with HMA-MMA whose HMA copolymer composition was 0.16 was compared with that in the linear PEO blends. The former blends were more miscible with HMA-MMA than the latter one by about 35 °C at the maximum cloud point temperature.     

Radical copolymerization of methyl 2-norbornene-2-carboxylate and 2-phenyl-2-norbornene with styrene, alkyl acrylate, and methyl methacrylate: Facile incorporation of norbornane framework into polymer main chain and its effect on glass transition temperature

Radical copolymerization behavior of methyl 2-norbornene-2-carboxylate 1 and 2-phenyl-2-norbornene 2 was investigated. Radical copolymerization of 1 and 2 with styrene, alkyl acrylate, and methyl methacrylate in a variety of monomer combinations afforded copolymers, whose main chains consisted of norbornane framework. Relative monomer reactivity ratios for the copolymerization of 1 and 2 with n-butyl acrylate (n-BA) were determined by the Fineman-Ross method. Temperature-modulated DSC analysis for poly(1 or 2-co-n-BA)s revealed remarkable T_g-raising effect of incorporation of norbornane framework into the polymer main chain, compared to that effect of styrene repeating unit.     

Novel miscible poly(ethylene sebacate)/poly(4-vinyl phenol) blends: Miscibility, melting behavior and crystallization study

High molecular weight samples of the novel biodegradable polyester poly(ethylene sebacate) (PESeb) were synthesized. Miscible poly(ethylene sebacate)/poly(4-vinyl phenol) semicrystalline/amorphous blends were prepared by applying the solvent casting method. Miscibility was proved by the single composition dependent glass transition temperature over the entire composition range observed in DSC traces of the quenched blend samples and also by the melting point depression. The Flory-Huggins interaction parameter was found to be x₁₂ = −1.3. Also, FTIR spectra supported the hypothesis of intermolecular interactions due to hydrogen bonding. The crystallization of PESeb in blends was studied. As expected, isothermal crystallization rates decreased in the blends with increasing the PVPh content. The Lauritzen-Hoffman analysis was tested. The values of nucleation constant K_g did not show any substantial variation. The non-isothermal crystallization of the blends was also tested. It was found that the crystallization is retarded in the case of blends, compared to the neat PESeb.     

Novel poly(arylene ether)s containing multi-substituted pentaphenylene moiety

Three novel 2-trifluoromethyl-activated bisfluoro monomers have been synthesized successfully using a Suzuki-coupling reaction of 4-fluoro-3-trifluoromethyl phenyl boronic acid with 4,4′-dibromo-p-terphenyls with varied phenyl substitution on the middle phenylene ring. Three monomers were converted to a series of phenyl substituted poly(arylene ether)s by nucleophilic displacement of the fluorine atoms on the terminal benzene ring with several bisphenols. The polymers obtained by displacement of the fluorine atoms exhibit weight-average molecular weight up to 2.25 × 10⁵ g/mol in GPC. Thermal analysis studies indicated that these polymers did not show melting endotherms but did show ultrahigh T_g values up to 334 °C in DSC and outstanding thermal stability up to 671 °C for 5% weight loss in TGA under nitrogen atmosphere. The polymers are soluble in a wide range of organic solvents: THF, CHCl₃, NMP, DMAc, DMF, toluene, etc., and are insoluble in DMSO and acetone at room temperature. Transparent and flexible films were easily prepared by solution casting from chloroform solution of each of the polymers. The UV absorption spectra of thin films showed no absorption in the visible light region of the spectrum, suggesting a good application to optical transparent materials in the visible light region of the spectrum.     

Evaluation of physico-chemical changes in sub-layers of multi-layer anticorrosive marine paint systems: Plasticizer and solvent release

Increased awareness of the environmental impact of solvent-based anticorrosive marine coatings has urged to predict long-term performance of a coating in order to make dry-docking less frequent. Each coating system was composed by three layers: topcoat, \ and primer. All samples were exposed to four different standard artificial weathering tests: a neutral salt spray test (NSS ISO 9227) and three cycles (QUV ASTM G53, ASTM D5894 and ISO 20340). Besides, the same samples were exposed to a natural weathering during 4 years in three different locations: Pipady (south of France), Kure Beach (North Caroline, USA) and Bandol (south of France). This research project focused exclusively on the degradation of the basecoat and primer by FTIR spectroscopy, PyGC/MS and dynamical mechanical analysis. Basecoat and primer binders formulated with dibutylphtalate as a plasticizer were found to strongly evolve during artificial cycle tests. An extensive diffusion of plasticizer was observed with a rise in T_g of the epoxy binder as high as 40 °C. The impact of these physico-chemical changes on the corrosion protection properties of the whole system were discussed based on electrochemical impedance spectroscopy (EIS) in 3 wt% NaCl solution, SEM observations, pull-off test and measurements of delaminated areas.     

Electrical and optical properties of a polyblend electrolyte

A potassium ion conducting polyblend electrolyte based on polyvinyl pyrrolidone (PVP)+polyvinyl alcohol (PVA) complexed with KBrO₃ was prepared using solution cast technique. The electrical conductivity increased with increasing dopant concentration. Optical absorption studies were made in the wavelength range (200-600 nm) on pure (PVP+PVA) and KBrO₃ doped (PVP+PVA) films. The absorption edge was observed at 5.13 eV for undoped (PVP+PVA) while it ranged from 4.88 to 5.0 eV for differently KBrO₃-doped samples. The direct band gaps for undoped and KBrO₃ doped (PVP+PVA) films were found to be, respectively, 5.05 and 4.95, 4.86 and 4.90 eV while the indirect band gaps were 5.03 and 4.88, 4.79 and 4.83 eV, respectively. The absorption edge and the band gaps moved towards lower energies as the dopant concentration was increased up to 20 wt% of the dopant. For further increase in dopant concentration these values started increasing again. This is explained in terms of formation of charge transfer complexes between the dopant and the host matrix. The thermal properties of these films were investigated with differential scanning calorimetry (DSC). The variation in film morphology is examined by scanning electron microscopic examination.     

Interactions of binary liquid mixtures with polysaccharides studied using multi-dimensional NMR relaxation time measurements

Nuclear magnetic resonance transverse T₂ relaxation time has proven to be a valuable parameter for characterizing liquid/polymer interactions. This measurement is applicable to many food, personal care, and cosmetic products that contain multi-component liquid mixtures. Here, we investigate the interactions of corn starch with water/glycerol mixtures of different weight compositions and explore liquid exchange dynamics; such a system is relevant to the personal care industry. We use a combination of chemical shift resolved ¹H T₂ relaxation measurements and corresponding two-dimensional T₂ relaxation exchange experiments using both a conventional experimental protocol and a modified method with the addition of NMR chemical shift selectivity. Two relaxation regimes were evident for the hydroxyl ¹H (found in both water and glycerol) whilst three relaxation regimes are evident for the aliphatic glycerol ¹H associated here with strongly bound, weakly bound, and free (bulk) liquid, respectively. At higher water contents preferential absorption of glycerol was evident. T₂-T₂ exchange maps with a range of storage times reveal molecular exchange rates between all three regimes due to self-diffusion. Rapid exchange of water between the bulk and bound locations was evident in the case of pure water. Exchange rates for hydroxyl ¹H was considerably reduced by the inclusion of glycerol.     

Improving coating resistance to acetic acid sterilisation: An EIS approach

In situ EIS spectroscopy was used to evaluate the performance of the inside coating of a deep-drawn polymer-coated steel can during sterilisation and pasteurisation with a 1% acetic acid solution. Acetic acid is a very common ingredient in filling goods and is a particularly aggressive substance for packaging materials. The in situ coating performance was correlated with polymer properties, like glass transition and thermal expansion.     

Synthesis,characterisation and enhanced properties of polyimide/mica hybrid films

Polyimide/mica (PI/mica) hybrid films were prepared from pyromellitic dianhydride/4,4-bis(3-aminophenoxy)biphenyl (PMDA/4,3-BAPOBP) and mica in a solution of N,N-dimethylacetamide. The structure–property relationships of the composites were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy and differential scanning calorimetry. FTIR indicated successful preparation of PI/mica hybrid films. XRD and SEM results indicated that the mica was well dispersed in the PI matrix. The dependence of morphology, glass transition temperatures (T_g), dielectric properties and mechanical properties at room temperature of the hybrid films on the content of mica was discussed. It was observed that T_g, the breakdown strength and tensile strength of the hybrid films, could be simultaneously increased when the mica content was lower than 8?wt-%. Meanwhile, the dielectric constant and dielectric loss of PI/mica hybrid films increased with the increase in the mica content.     

Segmented copolymers with monodisperse crystallizable hard segments: Novel semi-crystalline materials

Segmented block copolymers with short monodisperse crystallizable hard segments have interesting structures and properties. In the melt, such short monodisperse segments are miscible with the matrix segments. Moreover, upon cooling, they crystallize fast, demonstrating a very high crystallinity, and only a small crystallization window is needed. The melting temperature of the short segments is high, provided that they can H-bond and/or contain aromatic groups. The melting temperature was found to decrease with increasing matrix segment concentration, due to the solvent effect of the matrix segments. At concentrations of crystallizable segment of 4-35 wt%, good dimensional and solvent stabilities were obtained.The monodisperse segments crystallized into nano-ribbons with uniform thickness and high aspect ratio, and these dispersed nano-ribbon crystallites constituted physical crosslinks, while acting also as reinforcing fillers. At concentrations of the monodisperse segments below 20 wt% no spherulitic ordering took place, and the semi-crystalline polymers were transparent. The monodisperse crystallizable segments can be used in combination with matrix segments of either low or high glass transition temperature, and may even contain (bio)functional units.     

Two-dimensional correlation relaxometry studies of cement pastes performed using a new one-sided NMR magnet

We present preliminary results of the first NMR T₁-T₂ two-dimensional relaxation correlation experiments performed using a one-sided NMR system in cement based materials. Two-dimensional correlation relaxometry has itself only recently been demonstrated in cement paste where it proved to be a particularly sensitive probe of pore-water dynamics providing direct information on exchange of water between the gel and capillary pore networks. Further to this we have observed differences in the structural development of a selection of cement pastes throughout the early stages of hydration and verified the theoretical frequency dependence of the ratio T₁ / T₂. When coupled with instrumentation developments in one-sided NMR magnets the way is opened to detailed, spatially resolved studies of the development of hydration and porosity in the surface layers (top 50 mm) of cementitious materials. A new magnet, suitable for such applications, is discussed.     

Study on thermal transitions of toluene diisocyanate-based polyurethane elastomers with poly (tetramethylene oxide) as the soft segment by TSC/RMA, DSC and DMA thermal analyzers

Thermal transitions of TDI-based polyurethane elastomers with PTMO as the soft segment were characterized by the depolarization technique in TSC and by using with the thermal windowing technique on selected specimens in the RMA measurements. Results indicate that the broadened thermal transition in the glass transition region as observed in the DSC thermogram is related to the combined T_g transition and the T_global transition in the TSC spectrum. This T_global transition is associated with the macromolecular property as detected by tan δ in DMA measurement. The increase in the T_g with a high NCO content may be explained by the structural modification found on the urethanic chain with the additional linkage of the hard segment that affects the cooperative motion of the molecular chain. Data measured from DSC, TSC/RMA and DMA with simulated DEA and wide angle X-ray data are presented for the characterization of the polyurethanes. The RMA measurement leads to a compensation search on T_g transition and provides pertinent thermokinetic data that correlates the NCO content with changes in enthalpy and entropy on the relaxation behaviors in the T_g transition of polyurethane elastomers.     

Development of cantaloupe (Cucumis melo) pulp powder using foam-mat drying method: Effects of drying conditions on microstructural of mat and physicochemical properties of powder

In this study, the effects of drying conditions on moisture content, water activity (a_w), dissolution time, solubility, hygroscopicity, β-carotene, color, glass transition temperature (T_g), and sticky point temperature (T_s) of foam-mat-dried cantaloupe pulp powders and microstructure of dried cantaloupe pulp foams were investigated. Drying was performed in three temperatures (40, 55, and 70°C) on 3- and 5-mm thicknesses. The analysis of scanning electron microscopy micrographs with grey-level co-occurrence matrix showed that there is wide porous structure of dried foams at higher speeds drying. The temperature increase reduced moisture content and a_w, and increased hygroscopicity, and thickness rise increased moisture content and a_w and consequently decreased powders’ hygroscopicity under the same thickness and drying temperature, respectively. Increase in drying temperature would increase the reconstitution speed of powders into water and therefore the dissolution time decreased. In addition, results showed that the powder produced at 40°C have higher β-carotene content than those of produced at 55 and 70°C. With increasing drying temperature from 40 to 70°C, Lightness parameter (L) was increased while redness parameter (a) was decreased. The T_g and T_s were compared by plotting them in a graph against moisture content. For all drying processes the T_s was higher than the T_g. The drying conditions at 70°C (higher drying temperature) and 3?mm (lower thickness) led to a shorter drying time and consequent lower energy demand to produce a powdered cantaloupe pulp with high stability (low moisture content, a_w, and high T_g and T_s) and reconstitution speed of powder into water.     

NMR quantification of the partition of coronal chain segments of block copolymer vesicles

In vesicles of an ABC triblock copolymer, the soluble A and C blocks can be grafted onto the outer or the inner surfaces of the wall made of the insoluble B block. Traditionally, the determination of the fractions of A and B chain segments partitioned onto these two surfaces has been difficult. We show that they can be readily determined from NMR paramagnetic relaxation experiments. In such an experiment, a paramagnetic reagent that does not readily permeate the vesicular wall is added into a solution. This greatly shortens the spin-lattice relaxation times T₁ of these chain segments on the outer surface relative to those on the inner surface. Treating such T₁ relaxation data with a double exponential function yields the coefficients for these terms with different T₁ values and thus the relative populations for chain segments on the inner and outer vesicular wall surfaces. This method is simple and straightforward.     

g-B3N3C: a novel two-dimensional graphite-like material

A novel crystalline structure of hybrid monolayer hexagonal boron nitride (BN) and graphene is predicted by means of the first-principles calculations. This material can be derived via boron or nitrogen atoms which are substituted by carbon atoms evenly in the graphitic BN with vacancies. The corresponding structure is constructed from a BN hexagonal ring linking an additional carbon atom. The unit cell is composed of seven atoms, three of which are boron atoms, three are nitrogen atoms, and one is a carbon atom. It shows a similar space structure as graphene, which is thus coined as g-B₃N₃C. Two stable topological types associated with the carbon bond formation, i.e., C-N or C-B bonds, are identified. Interestingly, distinct ground states of each type, depending on C-N or C-B bonds, and electronic bandgap as well as magnetic properties within this material have been studied systematically. Our work demonstrates a practical and efficient access to electronic properties of two-dimensional nanostructures, providing an approach to tackling open fundamental questions in bandgap-engineered devices and spintronics.     

High strength polyimide fibers with functionalized graphene

Graphene possesses unprecedented physical and chemical properties and has been thought to be ideal filler for reinforcing fibers' mechanical properties. However, graphene is difficultly dispersed in polymer which severely restrict to prepare high-strength and high-modulus composites. In this work, we report an effective method to fabricate a kind of organ-soluble polyimide (PI)/graphene composite fiber using in situ polymerization. Graphene oxide (GO) is modified by 4,4′-diaminodiphenyl ether (ODA) to obtain the GO-ODA nanosheets which exhibit excellent dispersibility and compatibility with the organ-soluble PI matrix. WAXD results show that these 2D nanosheets have a significant influence on the crystallization, aggregation or assembly behaviors of the polymer chains. The PI/graphene composite fiber containing 0.8 wt% of GO-ODA presents a tensile strength of 2.5 GPa (1.6 times higher than the pure PI fiber), and tensile modulus of 126 GPa (223% raises compared with pure PI fiber). Furthermore, the incorporation of graphene significantly improves the glass transition temperature and thermal stability of the composite fibers. Thanks to the excellent hydrophobic properties of graphene, the hydrophobic behavior of the composite fibers is greatly improved. This effective approach shows a potential application in fabricating multifunctional polymer-based composite fibers.     

Effects of organoclay platelets on morphology and mechanical properties in PTT/EPDM-g-MA/organoclay ternary nanocomposites

The addition of up to 6 part per hundred (phr) of an organoclay to a 80/20 (w/w) PTT/EPDM-g-MA blend led to ternary compounds that came together as a means of balancing stiffness/strength versus toughness/ductility. The effect of organoclay platelets on morphologies and mechanical properties of PTT/EPDM-g-MA/organoclay ternary nanocomposites had been studied by SEM, TEM, WAXD, and mechanical testing. For the 80/20 (w/w) blend, the clay platelets are located inside the dispersed domains of EPDM-g-MA phase. The clay platelets do not act effectively as a barrier for the coalescence of the dispersed domains. The complex viscosities (η^∗) of the 80/20 (w/w) PTT/EPDM-g-MA blend increased with the amount of the organoclay increasing, which are proposed as the reason for the dispersed domain size (D) that becomes smaller at higher clay content. Mechanical tests show that the Young's modulus increases, whereas the tensile strength and the impact strength decrease when the content of the clay increases.