Allylic monomers as reactive plasticizers of polyphenylene oxide. Part III – Rheological and mechanical properties

The chemorheology of blends of diallyl ortho-phthalate (DAOP) as reactive plasticizer of polyphenylene oxide (PPO) were monitored during their cure with either dicumyl peroxide (DCP) or tert-butyl hydroperoxide (TBHP), and their mechanical properties and morphology were studied. The steady shear and dynamic rheology behaviour was consistent with chemical gelation of DAOP in blends with low concentrations of PPO but the gelation behaviour at higher PPO concentrations was more complex. Dynamic mechanical thermal analysis of the blends of PPO:DAOP cured with either DCP or TBHP indicated a two phase structure. For PPO:DAOP/DCP, the lowest transition (between 150 °C and 200 °C) was attributed to a DAOP-rich phase and its T_g was higher than that for pure DAOP/DCP due to the presence of PPO in the DAOP-rich phase. The smaller damping shoulder near 250 °C was caused by a PPO-rich phase with a T_g that was lower than pristine PPO due to the presence of unpolymerized or polymerized DAOP. In contrast, the glass transition region of the PPO:DAOP/TBHP system was very broad due to an overlap of the transitions for DAOP-rich and PPO-rich phases caused by higher levels of unpolymerized DAOP. SEM observations of the blends revealed a two phase morphology with PPO-rich particles in a poly-DAOP matrix for blends with ?30 wt% PPO, a co-continuous morphology for blends with 40 wt% PPO, and a phase inverted morphology with more than 50 wt% PPO. These SEM observations agree with studies of the swelling, disintegration or dissolution of matrix of the blends in solvent.     

An optimized preparation of bismaleimide–diamine co‐polymer matrices

The main aim of this study was to develop an improved method for the preparation of a bismaleimide–diamine (BMI/DDM) polymer matrix, achieving shorter curing time, longer processing time (pot life), and good thermal mechanical properties. A matrix of BMI/DDM thermoset was prepared at optimal conditions and formulation, containing BMI and DDM in a 2:1 mol ratio with 0.1 wt% of dicumyl peroxide (DCP) as the curing accelerator. An optimal temperature of 150°C was selected for both melt‐mixing and curing processes. The mechanism of matrix preparation was also investigated using differential scanning calorimetry and quantitative Fourier transformed infrared analysis. DCP at the optimal concentration was found to accelerate cross‐linking reactions between BMI and DDM without inhibiting the chain‐extension reaction of BMI. The specified formulation exhibited longer gel time (208 s/g) and shorter post‐curing time (2 h) compared to other formulations. In addition, thermomechanical behavior and thermal stability were analyzed by dynamic mechanical analysis and thermomechanical analysis, and thermogravimetric analysis, respectively. The storage modulus (E′), glass transition temperature (T_g), and decomposition temperature (T_d) of the BMI/DDM thermosets increased with the BMI content of the formulations, while the coefficient of thermal expansion and damping behavior (tan δ) decreased in a similar manner, primarily because of an increase in the degree of cross‐linking. Copyright © 2014 John Wiley & Sons, Ltd.     

Dynamic mechanical behavior of acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) blends

The dynamic mechanical behavior of uncrosslinked (thermoplastic) and crosslinked (thermosetting) acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) (NBR/EVA) blends was studied with reference to the effect of blend ratio, crosslinking systems, frequency, and temperature. Different crosslinked systems were prepared using peroxide (DCP), sulfur, and mixed crosslink systems. The glass‐transition behavior of the blends was affected by the blend ratio, the nature of crosslinking, and frequency. sThe damping properties of the blends increased with NBR content. The variations in tan δ_max were in accordance with morphology changes in the blends. From tan δ values of peroxide‐cured NBR, EVA, and blends the crosslinking effect of DCP was more predominant in NBR. The morphology of the uncrosslinked blends was examined using scanning electron and optical microscopes. Cocontinuous morphology was observed between 40 and 60 wt % of NBR. The particle size distribution curve of the blends was also drawn. The Arrhenius relationship was used to calculate the activation energy for the glass transition of the blends, and it decreased with an increase in the NBR content. Various theoretical models were used to predict the modulus of the blends. From wide‐angle X‐ray scattering studies, the degree of crystallinity of the blends decreased with an increasing NBR content. The thermal behavior of the uncrosslinked and crosslinked systems of NBR/EVA blends was analyzed using a differential scanning calorimeter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1556–1570, 2002     

Organic/Inorganic Hybrid Materials Based on Silsesquioxanes Derived from (3-Methacryloxypropyl) Trimethoxysilane and Their Blends with Vinylester Resins

The crosslinking of blends of a silsesquioxane (SSO) derived from (3-methacryloxypropyl) trimethoxysilane, variable amounts of a vinylester resin (VE, dimethacrylate of bisphenol A), and benzoyl peroxide (BPO) or dicumyl peroxide (DCP) as initiators, was followed by differential scanning calorimetry (DSC). For the neat SSO a thermally-initiated polymerization was observed in the 150–250°C range, leading to a conversion close to 22% of the initial C=C groups. The final conversion could be increased to a maximum value close to 83%, by adding an initiator and using a thermal cycle attaining temperatures in the range of 200°C. The use of variable amounts of VE as a co-monomer produced a slight increase of the final conversion in SSO/VE/BPO blends. Neither the conversion of double-bonds nor the addition of the VE had any effect on the onset temperature of thermal degradation, which was associated to the presence of the methacryloxypropyl groups supplied by the SSO and the VE resin. However, a distinct two-step degradation process was observed in the presence of VE. Coatings based on SSO/VE/BPO blends exhibited more uniform thicknesses and lower values of the microhardness than those devoid of VE. However, the conversion of C=C groups did not show any significant effect on the values of microhardness.     

Condensation of carboranes-12 with tri- and tetrachloroethylenes

The interaction ofortho-, meta-carboranes with tri- and tetrachloroethylene was investigated at 380°C in the absence of radical sources and at 150–200°C in the presence oftert-butyl peroxide.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, Moscow 117813. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 1020–1023, April, 1992.     

Thermal stability and structure of electroactive polyaniline-fluoroboric acid-dodecylhydrogensulfate salt

Oxidation of aniline by emulsion polymerization pathway using benzoyl peroxide oxidant in the presence of fluoroboric acid and sodium lauryl sulfate surfactant leads to incorporation of both acid group as well as surfactant group onto the polyaniline chain as dopants i.e. formation of polyaniline-fluoroboric acid-dodecylhydrogensulfate salt (PANI-HBF₄-DHS). Amount of dopants such as fluoroboric acid (HBF₄), dodecylhydrogensulfate (DHS) and water present in the PANI-HBF₄-DHS was found out for the first time. Electrochemical activity and rheological stability of the polymer were determined. Thermal stability of PANI-HBF₄-DHS was determined by subjecting the polyaniline salt in macroscale at four different temperatures (100, 150, 200 and 250 °C). Structure, composition and thermal stability of polyaniline salt were determined by chemical analysis, conductivity, IR, UV/vis, XRD spectral measurements from the heat treated samples. Polyaniline salt contains 8.3 wt% water, 22.4 wt% HBF₄ and 15.4 wt% DHS at ambient temperature. Upon vacuum, polyaniline salt loses 4.7 wt% water and on heating the sample at 100 °C it loses the remaining 3.6 wt% water. On further heating polyaniline salt loses its dopants and at 250 °C it loses both the dopants almost completely. Polyaniline salt on heating undergoes cross-linking even at 100 °C and however, conductivity (3 × 10⁻² S/cm) of polyaniline salt was found to remain almost the same up to 150 °C.     

Comparative study of isothermal and non-isothermal thermokevetic processes

In this paper a graphical and analytical method is presented for generating reaction isotherms from a set of non-isotherms andvice versa. The method was tested by using computer generated curves. The method was also checked by studying the kinetics of dehydration of calcium oxalate in a static atmosphere. The reaction was monitored in both non-isothermal (with nine heating rates between 0.5 and 60°C min^–1) and isothermal modes (at 150, 160 and 170°C). The 160°C isotherm obtained experimentally was compared with that obtained by graphical method from non-isotherms determined experimentally and the differences of were less than 3%.     

Effect of Initiator on the Over-Voltage Positive Temperature Coefficient of Linear Low Density Polyethylene/Carbon Black Nano Composites

The composite of linear low density polyethylene (LLDPE) with carbon black (CB) and inorganic flame retardant (aluminum hydroxide, Al(OH)₃) was prepared by melt-blending method. The effect of cross-linking on the stability of positive temperature coefficient (PTC) of composite and the elimination of negative temperature coefficient (NTC) of composite were investigated. LLDPE was chemically cross-linking with different contents of initiator (dicumyl peroxide, DCP). The cross-linking effects of composite were analyzed by gel content analysis, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). By the effect of DCP, not only the composite appeared a high PTC intensity, but also the NTC effect of composite was eliminated. In this investigation, the optimum PTC intensity of composite reached 5.87 orders of magnitude for the composition of LLD0.l0C33.7A28, and the PTC transitional temperature of composite decreased with increasing of DCP content. In addition, the good reproducibility of composites was proved by thermal cycling, and successfully passed the test of over-voltage resistance.     

Effect of gamma-irradiation on surface and catalytic properties of CuO−ZnO/Al2O3 system

A copper, zinc and aluminium mixed oxides sample having the nominal composition 0.25 CuO/0.03 ZnO/Al₂O₃ was prepared by impregnating Al(OH)₃ with copper and zinc nitrate solutions, drying at 100 °C then heating in air at 600 °C. The obtained solid was exposed to different doses of -rays (20–160 Mrad). The surface characteristics namelyS _BETV_P andr of different treated adsorbents were determined from N₂ adsorption isothems measured at –196 °C. The catalytic activity of various irradiated solids was determined by following up the kinetics of CO-oxidation by O₂ at 150–200 °C. The results showed that the doses up to 80 Mrad resulted in no significant change in theS _BET but increased slightly theV _P (20%) of the treated adsorbents. The irradiation at 160 Mrad caused an increase of 20% in theS _BET of the irradiated solid sample. The catalytic activity increased progressively by increasing the dose, a dose of 160 Mrad brought about an increase of 140% in the catalyst's activity. The apparent activation energy of the catalytic reaction decreased monotonically by increasing the absorbed dose of -rays which was attributed to a parallel induced decrease in the value of pre-exponential term of the Arrhenius equation. The observed increase in the catalytic activity due to -irradiation has been interpreted as a result of increasing the concentration of catalytically-active sites contributing in chemisorption and catalysis of CO-oxidation via a possible fragmentation of CuO crystallites.     

Novel amphoteric pH-sensitive hydrogels derived from ethylenediaminetetraacetic dianhydride, butanediamine and amino-terminated poly(ethylene glycol): Design, synthesis and swelling behavior

Novel amphoteric pH-sensitive hydrogels with pendant carboxyl and backbone tertiary amine groups were designed and synthesized. First, ethylenediaminetetraacetic dianhydride (EDTAD) reacted with butanediamine (BDA) via N-acylation reaction to give a polyamide prepolymer with pendant carboxyl groups (PEB–COOH); then amino-terminated poly(ethylene glycol) 500 (ATPEG500) was added as a cross-linking agent to produce the desired network polymer (PEB–ATPEG500–COOH). The obtained hydrogels are potentially degradable and non-toxic since its backbone and cross-linking sections are both linked by amide bonds and all monomers have been proved as safe. FTIR, ¹H NMR, ¹³C NMR and ninhydrin reaction method were employed to qualitatively and quantitatively characterize the obtained polymers. The effect of cross-linking agent amount, characterized by the molar ratios (R_m) of NH₂ groups in ATPEG500 to pendant COOH groups in PEB–COOH, on the swelling behavior of the proposed hydrogel was examined. The results indicate that the equilibrium swelling ratio decreases and the pH-sensitivity becomes retarded with the increase of R_m. For PEB–ATPEG500–COOH hydrogels with R_m no more than 0.42, they exhibited three SR_e variation zones at pH 2–4, pH 6–7 and pH 9–11, respectively, suggesting obvious and interesting amphoteric pH-sensitivity. In addition, the swelling kinetics tests on PEB–ATPEG500–COOH with R_m = 0.32 reveal that the swelling kinetics of proposed hydrogel follows a Fickian diffusion process in media of pH 7, and an anomalous diffusion process in media of pH 2 and 11. The above obtained results will facilitate the application of this proposed hydrogel in biomedical fields, particularly in the drug controlled release.     

Brønsted acid-base polymer electrolyte membrane based on sulfonated poly(phenylene oxide) and imidazole

The Brønsted acid-base polymer electrolyte membrane was prepared by entrapping imidazole in sulfonated poly(phenylene oxide) at the molar ratio of Im/SPPO = 2:1. The hybrid showed a high thermal stability up to 200 °C and peroxide tolerance. Differential scanning calorimetry shows that glass transition temperature is 232 °C. The conductivity increases with temperature exceeding 10⁻³ S/cm above 120 °C and a high conductivity of 6.9 × 10⁻³ S/cm was obtained at 200 °C under 33% RH conditions.     

Allylic monomers as reactive plasticizers of polyphenylene oxide. Part II: Cure kinetics

As part of an investigation of the processing of polyphenylene oxide (PPO) with polymerisable plasticizers, the curing kinetics of various diallylic monomers – diallyl ortho phthalate (DAOP), diallyl terephthalate, triethylene glycol diallyl ether and diethylene glycol diallyl carbonate) – and triallylic – triallyl cyanurate and triallyl isocyanurate – with radical initiators of differing activity were studied. All the monomers exhibited similar cure kinetics with each initiator and the exotherm peak temperatures correlated well with the reactivity of the initiators as measured by the 1 h half-life temperatures. Multiple scan-rate dynamic DSC studies gave similar activation energies to those obtained from isothermal rheology studies of gelation. The effects of the presence of PPO on the curing of diallyl ortho phthalate (DAOP) were studied using dicumyl peroxide (DCP) and tert-butyl hydroperoxide (TBHP) as initiators and differing behaviour was observed. In the PPO:DAOP/DCP system, the reaction rate was reduced with increasing PPO due to a dilution effect but the heat of reaction was generally unaffected. However, in the PPO:DAOP/TBHP system, a significant increase of cure rate was observed in the presence of 20 wt.% PPO due to the catalysis of TBHP by Cu²⁺ and Co³⁺ impurities in the PPO, but the cure rate was slightly reduced with increasing PPO content. In addition, the heat of polymerisation for the PPO:DAOP/TBHP blends were usually less than that for the pure monomer. This information can be used in the processing of PPO with DAOP as a polymerisable plasticizer.     

Changes in sol fraction during peroxide crosslinking of linear low-density polyethylenes with homogeneous distribution of short chain branching

FTIR measurements of sol fractions were carried out in order to assess side reactions during dicumyl peroxide (DCP) crosslinking of linear low density polyethylenes (LLDPEs) with homogeneous distribution of short chain branching. The changes of methyl and olefinic unsaturation concentration were measured as a function of degree of branching and DCP content. The changes of methyl and vinylidene concentration indicate that the scission probability has greater significance for the samples with initial branch content above 31 CH₃/1000 C and increases with increasing DCP concentration. The analysis of trans-vinylene concentration indicates that the probability of disproportionation also increases with increasing DCP content. The changes of methyl concentration in the sol fraction of the sample containing initially ca. 23 CH₃/1000 C with increasing DCP content could be interpreted using the dependence of crosslinking efficiency on branch content found previously for some range of branch concentration. © 1995 John Wiley & Sons, Inc.     

Study of the formation and stability of the Pd and Pt metallic nanoparticles on carbon support

Catalysts containing Pd and Pt on a Sibunit carbon support were studied by the temperature-programmed reduction, in situ X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy (XAFS). The reduction of Pd and Pt species in samples 2%Pd/C and 2%Pt/C calcined in an air flow at 370°C was studied. Reduction of the 2%Pd/C sample begins at 50—60 °C and is completed at 250—300°C. Particles of various dispersion are formed during reduction. Long-distance peaks observed in the EXAFS spectra point to the presence of a fraction of relatively large crystallites. The average Pd—Pd coordination number (5) at 200 °C gives evidence that a number of very small Pd nanoparticles, oligomeric clusters, is present. Reduction at T > 200°C results in sintering of a small fraction of the Pd particles. Reduction of Pt in 2%Pt/C sample begins at 120—150 °C and is completed at 300—350°C. The sintering-resistant monodispersed Pt particles are formed under these conditions.     

The effects of thermal treatment on the antioxidant activity of polyaniline

The thermal stability of chemically synthesized polyaniline (PANI) was examined, including granular (G) polyaniline powders formed conventionally in an HCl medium, and nanorod (NR) samples prepared using a falling-pH synthesis. The samples were examined before and after dedoping (dd) using thermogravimetric analysis (TGA), which showed small mass losses in the 200-300 °C temperature range, and greater mass losses due to oxidative degradation at higher temperatures. Furthermore, samples were treated thermally at 100, 125, 150, 175, 200, 250 and 300 °C for 30 min in air. SEM images did not show any pronounced effect on the morphologies of the samples from thermal treatment up to 300 °C. The ratios of the intensities (Q/B) of the predominantly quinonoid (Q) and benzenoid peaks (B) from FTIR spectroscopic analysis revealed that NR-PANI and NR-PANIdd underwent cross-linking upon thermal treatment up to 175 °C and were oxidized after treatment above 175 °C. G-PANI and G-PANIdd also underwent the same chemical changes with oxidation occurring above 200 °C. The free radical scavenging capacity of the samples was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, and was found to be independent of the spin concentrations of the samples. All samples exhibited a rapid decline in free radical scavenging capacity when exposed to temperatures above 200 °C, indicating that any polymer processing should be undertaken at temperatures less than this value to achieve high antioxidant activity.     

Peroxide-initiated condensation of carboranes-12 with 1,2-dichloroethylene

The interaction of carboranes-12 with 1,2-dichloroethylene was investigated at 150–200°C in the presence oftert-butyl peroxide as an initiator.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, Moscow 117813. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 1017–1019, April, 1992.     

Transmission electron microscopy study of phase morphology in polypropylene/ethylene-octene copolymer blends

Blends of polypropylene (PP) and ethylene-octene copolymers (EOC) were investigated by transmission electron microscopy (TEM) and by differential scanning calorimetry (DSC). The EOC contained 28, 37, 40 or 52 wt% of octene. Only the 50/50 PP/EOC ratio was used for all blends. None of the blends was fully miscible, there was always two-phase morphology. TEM observation followed by image analysis by ImageJ software revealed that the largest particles were in blend containing EOC-28 and the smallest were in blend with EOC-52. The coarsening rate at 200 °C was evaluated by TEM. The glass transition temperature (T_g) shift indicated partial miscibility. Partial miscibility was then confirmed by direct observation of bright PP lamellae in EOC dark phase.     

Study of the high temperature reactions of a hindered aryl phosphite (Hostanox PAR 24) used as a processing stabiliser in polyolefins

The processing stabilising performance of various phosphorous antioxidants in polyolefins is affected significantly by their chemical composition. In order to explore the mechanism of stabilisation, the reactions of a hindered aryl phosphite [tris(2,4-di-tert-butylphenyl)phosphite (DTBPP), Hostanox PAR 24] were investigated at temperatures corresponding to polyethylene processing. The thermal and thermo-oxidative stability of the additive was determined by differential scanning calorimetric (DSC) and thermogravimetric methods. DTBPP was heat treated under argon and oxygen at 200 and 240 °C. The stabiliser was reacted at 200 °C with azobisisobutyronitrile (AIBN) in oxygen-free environment (carbon centred radicals) and under oxygen (peroxy radicals), with dicumyl peroxide (DCP) in oxygen atmosphere (oxy radicals), and with cumene hydroperoxide (CHP) under argon. The reaction products were identified by FT-IR, HPLC and HPLC-MS. The results revealed that besides the known reactions of hindered aryl phosphites, thermal decomposition and recombination reactions also take place above the melting point of the antioxidant. DTBPP does not react with molecular oxygen, but its decomposition is accelerated by oxygen and especially by radicals. Accordingly, the heat-stability of phosphorous stabilisers also has to be taken into account in their application, as it is one of the factors which influence the processing stabilisation of polyolefins.     

Effects of gamma-irradiation and Li2O-doping on surface and catalytic properties of unloaded Co3O4 solid

The effects of -irradiation (20–160 Mrad) and lithium oxide doping (0.75–6 mol%) on the surface and catalytic properties of unloaded Co₃O₄ solid have been investigated. The surface characteristics of various solids were determined from nitrogen adsorption isothems taken at –196 °C and their catalytic activities were measured by following the kinetics of CO-oxidation by O₂ at 100–150 °C using a static method. The results showed that -rays brough about a decrease of 21% inS _BET of Co₃O₄ due to widening of its pores and led also to a considerable increase in its catalytic activity. A maximum increase of 91% was observed upon exposure to a dose of 80 Mrad. Lithium oxide-doping at at 500 °C resulted in an increase of 150% inS _BET of treated solid without changing its mean pore radius. This treatment was also accompanied by an increase of about 50% in its catalytic activity measured at 150 °C. Gamma-irradiation and Li₂O-doping of unloaded Co₃O₄ did not change the magnitude of apparent activation energy of catalysis of CO-oxidation by O₂ but increased the concentration of catalytically active sites contributing in the catalytic process. In other words, -rays and lithium oxide doping did not alter the mechanism of catalytic oxidation of CO by O₂ over unloaded cobaltic oxide solid.     

Study on the hydrothermal reaction of FeCl<Subscript>3</Subscript> solution in the presence of poly(vinyl alcohol)

A 0.5 dm³ aqueous solution of 0.1 M FeCl₃ dissolving 1 wt% poly(vinyl alcohol) (PVA) was treated hydrothermally in a stainless steel autoclave at various temperatures (T _h=110–200 °C). Highly ordered red corpuscle-like hematite particles around 2 m in diameter were produced after aging the solution at T _h=110 °C for 7 days, though large numbers of spherical PVA microgels around 2–4 m in diameter were produced together with the red corpuscle-like particles at T _h120 °C. The number of red corpuscle-like hematite particles decreased but that of spherical PVA microgels increased with increasing T _h, leading to the proposal that the method carried out in the present study will become a new synthetic method of polymer microgels. The ferric ions acted as a cross-linking agent to make PVA insoluble in water. The red corpuscle-like hematite particles produced at T _h=110 °C had high specific surface areas and showed high mesoporosity. The mesoporosity appeared to be more pronounced after evacuating the particles above 300 °C. The diameter of the mesopores after evacuation above 300 °C ranged from 2 to 20 nm, with a maximum at around 5–6 nm. The H₂O and N₂ adsorption experiments revealed that there are no ultramicropores in the particles. The H₂O and CCl₄ adsorption experiments further disclosed that the surface hydrophobicity of the particles is low even though PVA molecules remain after evacuation of the particles at 100–400 °C. Furthermore, the micropores produced after evacuation of the particles at 400 °C exhibited a high size restriction effect, i.e., the micropores produced were accessible to H₂O (diameter 0.253 nm) and N₂ (diameter 0.318 nm) molecules but not to CCl₄ (diameter 0.514 nm).