Copolymerization via zwitterion of 2-ethyl-2-oxazoline with β-methylhydrogenitaconate

Summary 2-Ethyl-2-oxazoline (ETOX) as a nucleophilic monomer and -methylhydrogenitaconate (MHI) as electrophilic monomer were copolymerized in solution in the absence of initiator at various feed mole ratios. Copolymers were characterized by elemental analysis, FT-IR and ¹H NMR spectroscopy. The copolymer composition was determined by elemental analysis and by ¹H NMR spectroscopy. The copolymerization reaction occurs with a termination reaction which is evidenced by the end double bond at the ¹H NMR spectra.     

Synthesis and characterization of biodegradable copolymers based on 6-aminocaproic acid and α-L-alanine

Random copolymers based on 6-aminocaproic acid and α-L-alanine were prepared by melt phase polycondensation method and characterized by FTIR, ¹H NMR, DSC and WAXD. The density, water absorptivity and enzymatic degradation of copolymers were measured. The results show that with increasing of alanine content in comonomers, the density, water absorptivity and rate of enzymatic degradation of copolymers increase, but the intrinsic viscosity and the degree of crystallization decrease. When the molar percentage of alanine increases to 40% in comonomers, copolymer is amorphous.     

Synthesis and properties of novel donor–acceptor copolymers based on thiophene and squaraine moieties

Two novel donor–acceptor copolymers were synthesized by Sonogashira cross-coupling of alkyl/alkoxy thiophene and dibromo-substituted squaraine moieties. The structures and properties of these polymers were characterized using FT–IR, NMR, UV–Vis, gel permeation chromatography, and cyclic voltammetry. Both copolymers are readily soluble in common organic solvents. The polymer films exhibit broad absorption in the wavelength range from 300 to 1000 nm with the maximum peaks over 750 nm. Electrochemical studies reveal that the band gaps of the polymers range from 1.05 to 1.36 eV. Compared to the alkyl thiophene, the alkoxy thiophene units can effectively lower the band gap and result in significant red-shift absorption spectrum of the resulted polymer. The strong overlap of the solar spectrum and the extremely low band gaps of the polymers suggest that they may be promising candidates for solar cells.     

Preparation and characterization of polyseudorotaxanes based on adamantane-modified polybenzoxazines and β-cyclodextrin

β-Cyclodextrin (β-CD) forms inclusion complexes (ICs) with adamantane-modified benzoxazines (2 benzoxazine and 3 benzoxazine). These benzoxazines can readily penetrate into the CD's hydrophobic cavity, causing turbidity of their solutions, from which fine crystalline powders are obtained. We characterized these complexes by powder X-ray diffraction, ¹³C and ¹³C CP/MAS NMR spectroscopies, DSC, and TGA. The X-ray diffraction and solid-state ¹³C CP/MAS NMR spectroscopy indicate that the IC domains of the polypseudorotaxanes maintain their channel-type structures after the ring-opening curing reactions have occurred. Furthermore, DSC measurements indicate that complexing the adamantane-modified benzoxazine units with β-CDs result in stiffer main chains and, thus, higher glass transition temperature. TGA also indicates that the inclusion complexes have enhanced its thermal stability.     

Effects of Mn-doping on the structure and in vitro degradation of β-tricalcium phosphate

β-tricalcium phosphate (β-TCP) is an ideal biomaterial for the bone repair because of its biocompatibility and biodegradability. In this study, 0 mol%, 5 mol%, 15 mol% and 30%mol bivalent manganese ion (Mn²⁺) doped β-TCP (Mn-TCP) powders were synthesized by a sol-gel method. The amount of the dopants significantly influences the crystallinity and the parameters related with structure of β-TCP, such as the lattice parameters and crystallite dimensions. The particle size and the particle distribution of doped β-TCP powers were evaluated as well. Meanwhile, the as-synthesized powders were consolidated by sintering at 1000 °C in muffle furnace for 5 h to get Mn-TCP porous material and the degradation experiment was carried out in Simulated Body Fluid (SBF) solution for 28 days. Then, Mn-TCP porous material were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM). Significantly, there were bone-like apatite materials deposited on the surface of bone-like porous materials. With the increasing doping amount of Mn²⁺, the newly formed apatite-like materials decreased, while the crystallinity increased significantly. Besides, pH results showed that alkaline environment was more favorable for the formation of sedimentary materials.     

Alternating copolymers based on 1-methylpyrrole and thiophene – synthesis and electrochemical studies

The synthesis and electrochemical polymerisation behaviour of a series of monomers containing 1-methylpyrrole and thiophene is reported. These monomers provide copolymers of well defined monomer sequence in the backbone. Received: 30 October 1997/Revised version: 26 November 1997/Accepted: 27 November 1997     

Quantitative prediction of elastomer degradation and mechanical behavior based on diffusion–reaction process

Thermal oxidative aging and other chemical-induced degradation greatly affect the service life of elastomer components. In this article, we presented a strategy to predict the long-term mechanical behavior of elastomeric components, to foresee the failure of elastomer components in design stage. The accumulation and consumption of small molecule reactants in elastomers are described using a diffusion–reaction process. Free-volume theory is applied to consider the diffusivity change during this process. Degradation of elastomers under elevated temperature up to 500 K, environmental pressure up to 4 atm, and different cross-link densities are studied in this simulation. Methodology of prediction of mechanical behavior is proposed based on the affined network model.     

Effects of β-carotene and lycopene thermal degradation products on the oxidative stability of soybean oil

The relative oxidative stability of soybean oil samples containing either thermally degraded β-carotene or lycopene was determined by measuring peroxide value (PV) and headspace oxygen depletion (HOD) every 4 h for 24 h. Sobyean oil samples containing 50 ppm degraded β-carotene that were stored in the dark at 60°C displayed significantly (P<0.01) higher HOD values compared with controls. Lycopene degradation products (50 ppm) in soybean oil significantly (P<0.05) decreased HOD of samples when stored in the dark. PV and HOD values for samples containing 50 ppm of either β-carotene or lycopene degradation products stored under lighted conditions did not differ significantly from controls (P<0.05). However, soybean oil samples containing 50 ppm of unheated, all-trans β-carotene or lycopene stored under light showed significantly lower PV and HOD values than controls (P<0.01). These results indicated that during autoxidation of soybean oil held in the dark, β-carotene thermal degradation products acted as a prooxidant, while thermally degraded lycopene displayed antioxidant activity in similar soybean oil systems. In addition, β-carotene and lycopene degradation products exposed to singlet oxygen oxidation under light did not increase or decrease the oxidative stability of their respective soybean oil samples.     

Effects of electron beam irradiation on the structure–property behavior of blends based on low density polyethylene and styrene-ethylene-butylene-styrene-block copolymers

Low density polyethylene (LDPE) blends with different additives were exposed to various doses of electron beam irradiation. The additives used were styrene-ethylene-butylene-styrene-block copolymers (SEBS), styrene-ethylene-butylene-styrene-block copolymer grafted with maleic anhydride (SEBS-g-MA) and mineral compounds. The structure–property behavior of electron beam irradiated blends was characterized in terms of mechanical, thermal, and electrical resistivity properties. The results indicated that the unirradiated LDPE blends with the different compositions showed improved mechanical properties, thermal and volume resistivity properties than pure LDPE. However, the improvement in properties of unirradiated blends by using SEBS-g-MA was higher than using SEBS copolymer. Further improvement in the mechanical, thermal and electrical properties of the LDPE blends was achieved after electron beam irradiation. The limited oxygen index (LOI) data revealed that the LDPE/SEBS-g-MA/ATH blend was changed from combustible to self-extinguishing material after electron beam irradiation to a dose of 100 kGy. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of Ta2O5 additions on phase formation during synthesis and sintering of β-alumina based ceramics

Conclusions We demonstrated the effect of the Ta₂O₅ additive on the process of phase formation during the synthesis of the powders and during sintering of -alumina ceramics (as compared to stoichiometric sodium polyaluminate Na₂O·5Al₂O₃). The presence of the additive increases the quantity of -Al₂O₃ phase and stabilizes it during low-temperature isothermal synthesis; during high-temperature sintering, it hinders the formation of the nonconducting -Al₂O₃ phase; this is one of the main conditions required for obtaining -alumina ceramics having a high ionic conductivity.Translated from Ogneupory, No. 2, pp. 13–15, February, 1991.     

Thermal and chemical effects of nucleating agents on α, β, γ-polymorphism of isotactic polypropylene

Isotactic polyprpylene (iPP) occurs in several crystalline forms, denoted as f (monoclinic), g (hexagonal), and n (orthorhombic) phases. Hot-stage microscopy, differential scanning calorimetery, and wide-angle X-ray diffraction were used to investigate the influence of thermal treatment and nucleating agents on the morphology of iPP matrices. The tendency of glass fiber (GF) and Kevlar aramid fiber (KF) to induce transcrystallinity in different iPP matrices was evaluated. The f form was present in all iPP specimens treated by different nucleating agents at different crystallization temperatures (Tc). The g and n forms (impure) were found only in iPP specimens that were treated with g -nucleating agent and n - nucleating agent, respectively. Development of transcrystallization was found to depend on the type of fiber used, nucleating agents, and Tc. It was observed that the crystallinity content, obtained by applying different thermal treatments (slow cooling or quenching), gave rise to different morphologies of iPP matrices.     

The Effect of Zn-Al-Hydrotalcites Composited with Calcium Stearate and β-Diketone on the Thermal Stability of PVC

A clean-route synthesis of Zn-Al-hydrotalcites (Zn-Al-LDHs) using zinc oxide and sodium aluminate solution has been developed. The as-obtained materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The effects of metal ions at different molar ratios on the performance of hydrotalcites were discussed. The results showed that the Zn-Al-hydrotalcites can be successfully synthesized at three different Zn/Al ratios of 3:1, 2:1 and 1:1. Thermal aging tests of polyvinyl chloride (PVC) mixed with Zn-Al-LDHs, calcium stearate (CaSt(2)) and β-diketone were carried out in a thermal aging test box by observing the color change. The results showed that Zn-Al-LDHs can not only enhance the stability of PVC significantly due to the improved capacity of HCl-adsorption but also increase the initial stability and ensure good-initial coloring due to the presence of the Zn element. The effects of various amounts of Zn-Al-LDHs, CaSt(2) and β-diketone on the thermal stability of PVC were discussed. The optimum composition was determined to be 0.1 g Zn-Al-LDHs, 0.15 g CaSt(2) and 0.25 g β-diketone in 5 g PVC.     

Crosslinkable surfactants based on linoleic acid-functionalized block copolymers of ethylene oxide and ε-caprolactone for the preparation of stable PMMA latices

Amphiphilic diblock and triblock copolymers consisting of poly(ethylene oxide) (PEO) as (central) hydrophilic segment and poly(ε-caprolactone) (PCL) as hydrophobic segment(s) were prepared by ring opening polymerization. The length of the PEO segment was kept constant , whereas the length of the PCL block(s) was either 6 or 10 units for diblock copolymers and 3 or 5 units at each end for the triblock copolymers. These block copolymers were end-functionalized by esterification with linoleic acid (LA), which contains reactive double bonds. The autoxidative behavior of PEO₄₅-(CL₃-LA)₂ functionalized triblock copolymers was investigated by exposure of films to air at ambient conditions. Ninety percent of the double bonds had disappeared in 15 d and a crosslinked structure was obtained after 30 d. Critical micelle concentrations (CMC) of the crosslinkable surfactants were in the range of 0.08-0.19 mmol/l for the diblock copolymer and of 0.19-0.26 mmol/l for the triblock copolymer. The surface tension of aqueous surfactant solutions at the CMC (γ_CMC) (25 °C) varied from 47.1 to 51.4 mN/m for the diblock and from 45.6 to 48.1 mN/m for the triblock systems. For both systems CMC and γ_CMC increase with increasing HLB values. These surfactants were used in PMMA latex preparations. The latices of PMMA prepared with LA-functionalized diblock and triblock copolymers yielded narrow particle size distributions and particle sizes of 180 and 370 nm, respectively, whereas latices prepared with SDS had a particle size of 90 nm. After extraction of the latex particles with methanol, the amounts of the unextractable (either buried or copolymerized) LA-functionalized diblock and triblock copolymers found in extracted PMMA latex particles were 10 and 24% of the initial amount of surfactant added respectively. Control experiments with a stearic acid (SA) containing diblock copolymer showed that the amount of buried surfactant in PMMA latices was 6.5%. By comparing the overall latex characteristics and stability (shelf stability, freeze-thaw testing and addition of electrolyte solutions and ethanol) it was concluded that an LA-functionalized diblock copolymer (MPEO₄₅-CL₁₀-LA) gave better stabilization of PMMA latices than an LA-functionalized triblock copolymer of comparable composition and HLB value.     

Synthesis, morphology and mechanical properties of linear triblock copolymers based on poly(α-methylene-γ-butyrolactone)

A series of well-defined triblock copolymers containing middle soft poly(n-butyl acrylate) (PBA) block and outer hard blocks of poly(α-methylene-γ-butyrolactone) homopolymer (PMBL) or random poly (α-methylene-γ-butyrolactone)-r-poly(methyl methacrylate) copolymer (PMBL-r-PMMA) were synthesized by atom transfer radical polymerization (ATRP). Phase separated morphologies of cylindrical or spherical hard block domains arranged in the soft PBA matrix were observed by atomic force microscopy and small-angle X-ray scattering. The mechanical and thermal properties of the copolymers were thoroughly characterized and their thermoplastic elastomer behavior was studied. Dynamic mechanical analysis (DMA) showed for all PMBL-b-PBA-b-PMBL copolymers a very broad rubbery plateau range extending up to temperatures of 300 °C. Replacement of the PMBL hard block with the less brittle PMBL-r-PMMA resulted in an improvement of the tensile properties, without compromising the very good thermal stability of the materials.     

Thiocarbonyl compounds from β-substituted vinylald- and -ketimmonium derivatives

Results on the synthesis of thiocarbonyl compounds based on the reactions of conjugated unsaturated immonium salts with S-nucleophiles are summarized, and the physical and chemical properties as well as the synthetic potential of forming α, β-unsaturated thioaldehydes and thioketones are considered.     

Thermal shock properties of β-sialon ceramics

An indentation–quench method based on Vickers cracks for measuring thermal-shock properties has been applied to β-sialon materials. The thermal-shock properties have been correlated with the morphology of the β-sialon grains, the z value in the β-sialon solid solution Si_6−zAl_zO_zN_8−z and the amount of residual intergranular glass phase. z Values in the range 0.6–3.0 were tested, and the amount of residual yttrium-containing glass phase was varied between 0 and 20 vol.%. The best thermal-shock resistance was found at low z values, and was further improved by adding an intergranular glass phase. The poorest resistance to thermal shock was found for the highest z value where the presence of glass had no measurable influence. One composition (z=1.5, 10 vol.% glass) was selected for studying the influence of the microstructure on the thermal-shock properties. The microstructure was varied by applying different sintering conditions. An improvement of the thermal-shock properties and the fracture toughness was found in samples containing elongated β-sialon grains formed in situ. In general, in-situ reinforced β-sialon materials with low z values and containing an intergranular glass phase exhibited the best thermal-shock resistance and improved fracture toughness (K_1c>4 MPa m^{$\text{1}\text{2}$}).     

Thermal conductivity of combustion synthesized β-sialons

To the first time, thermal conductivities of spark plasma sintered β-sialons (Si₃Al₃O₃N₅) procured from combustion synthesis (CS) with no sintering additive were measured by the laser flash method at room temperature. A full densification occurred when these materials were sintered at 1600 °C with a simultaneous pressure of 50 MPa. XRD analyses indicated that single phase β-sialons were formed after SPS though the combustion synthesized β-sialon powders had considerable amounts of silicon impurities. Thermal conductivity values increased with sintering temperature and attained a maximum of 5.49 W m⁻¹ K⁻¹ for fully densified β-sialons sintered at 1700 °C for 10 min.     

Thermal degradation of microporous Sm2O3–MgO nanocomposites at isothermal conditions and surface chemical properties

The evolution of microstructural, morphological and surface chemical properties of Sm₂O₃–MgO nanocomposites are determined during and after isothermal heat treatments in the range of 500–1000 °C. The samples are investigated using (high temperature) X-ray diffraction, energy-filtered transmission electron microscopy including electron energy loss spectroscopy, nitrogen adsorption, and temperature programmed desorption of CO₂. With small amounts of MgO the initial micropore fractions are low and mainly coarsening of Sm₂O₃ is observed. Large amounts of MgO result in high initial micropore fractions giving rise to enhanced densification. The different thermal degradation behaviors are explained by means of the respective characteristic diffusion distances which are determined by the volume phase fractions. The surface chemical properties of Sm₂O₃ and MgO remain qualitatively unchanged, however, the specific CO₂ chemisorption capacities are increased through the nanocomposite formation.     

Chemisorption of halogen on carbon—II Thermal reversibility of Cl2, HCl and H2 chemisorption

There are surface double bonds on carbons which differ from the graphitic surface π-bonds in their chemical reactivity. They may be created by degassing prechlorinated or prehydrogenated carbon samples, besides their natural occurrence in nontreated carbons.Cl₂, H₂ and HCl may be added to these double bonds and partially degassed by thermal cycling in presence of the gases. This indicates that at least part of these olefinic bonds are thermally labile and are, therefore, important for catalysis and surface chemical modifications of carbons. The surface concentration of the labile bonds is low, amounting to a few hundredths of meq/100m² of carbon surface area. Discrimination between physisorption and chemisorption of H₂ on carbon can be made by analysis of the dependence of adsorption on temperature. With Cl₂, considerable overlap between the two processes takes place.