Cinnamylidene-amine-sensitized photodegradation of polyethylene

The activity of Schiff's bases of cinnamic aldehyde and aromatic amines in the controlled photodegradation of polyethylene (PE) was studied. N-cinnamylidene anilines containing different substituents in the amine ring (methyl group, halogen, or amine group) and N-cinnamylidene α-naphthyl amine were synthesized and introduced into the polyethylene films by compression molding or extrusion, and they were exposed to the filtered ultraviolet light produced by mercury lamp. The changes in molecular weight, tensile strength, and characteristic IR absorptions were followed during irradiation to control the processes undergoing in the polymer films. It was discovered that N-cinnamylidene anilines containing methyl or halogen substituents and N-cinnamylidene α-naphthyl amine accelerated the photodegradation of polyethylene. Their sensitizing activity increased when the mixtures of Schiff's bases and stannous laurate were introduced into the polymer. PE films containing these additives became brittle after 600 h exposure to the artificial UV light which was the equivalent of 1.5–2 years exposure to the natural sunlight in the medium geographic latitudes. The mechanism of the initial step of photodegradation is discussed.     

Electrospun nanofibers from ferrocene-containing multiblock copolymers prepared via RAFT polymerization with F127 modified precursor

Electrospun nanofibers from copolymers composed of ferrocene side chains and PEO₁₀₀-PPO₆₅-PEO₁₀₀ (F127) were fabricated in chloroform and N,N–dimethyl formamide solutions (V/V = 95:5) at room temperature. Ferrocene-containing multiblock copolymers (PFcMA_n-F127-PFcMA_n) were synthesized through reversible addition-fragmentation chain transfer polymerization using s-1-dodecyl-s''- (α, α'-dimethyl-α''-acetic acid) trithiocarbonate (DDMAT) modified F127 with 2- (methacryloyloxy) ethyl ferrocencarboxylate (FcMA). The structures of as-obtained chemicals were characterized by FTIR, ¹H NMR, and ¹³C NMR. Additionally, the block copolymers molecular weight and polydispersity were measured using gel permeation chromatography. The electrochemical responsiveness of the polymers was investigated using cyclic voltammetry as well as the thermal stabilities of polymers and precursors were tested through DSC and TGA. The morphologies of electrospun fibers were observed through field emission scanning electronic spectroscopy and a fibrous diameter of 300–1100 nm was obtained. The results indicated that the suitable molecular weight of ferrocene -containing polymer would be processed in nanofibrous.     

Structure–property relationships in copolymers to composites: Molecular interpretation of the glass transition phenomenon

Structure is taken as the main theme in outlining the mechanical properties of polymer composites. Examples of two-component polymer systems are selected from the literature showing their morphology, as evidenced from electron micrographs, and their corresponding mechanical properties, as evidenced by dynamic mechanical spectra. A compatibility number, N_c, is defined in a continuous scheme from a compatible system (one glass transition, N_c → ∞) to an incompatible system (two glass transitions, N_c → 0). The point at which semicompatibility occurs, N_c ? 1, is taken as the approximate universal segmental length associated with a glass transition. This length of 150 Å allows for 100 to 5000 C? C bonds for an associated glass transition. The ramifications of this molecular interpretation of a glass transition are discussed, resulting in a denouncement of the time–temperature correspondence principle and a new interpretation of short-segmental block copolymers.     

Synthesis,characterization, and magnetic properties of α-MnS nanocrystals

MnS nanocrystals have been prepared by a colloidal synthesis route through the reaction of MnCl₂ and S[Si(CH₃)₃]₂ in trioctylphosphineoxide. The nanocrystals were characterized using X-ray diffraction and transmission electron microscopy. The magnetic properties were studied with SQUID magnetometry. X-ray diffraction shows that the nanocrystals are of the thermodynamically stable α-MnS (alabandite) structure. Size control was achieved by changing the concentration of the precursors. Nanocrystal sizes were measured by transmission electron microscopy, and three samples of average diameters 20, 40, and 80 nm were obtained, with narrow size distribution (σ˜9%). The zero field cooled magnetization curves for the 80-, 40-, and 20-nm samples showed a cusp at 116 K, 97 K, and 50 K respectively, all smaller than the antiferromagnetic transition temperature, T_N = 130 K, of bulk α-MnS. Below T_N the magnetization exhibits a paramagnetic behavior unlike typical antiferromagnetic materials. These results indicate that there is a mixture of paramagnetic and antiferromagnetic phases in the nanocrystals. The size dependence shows a general trend of decrease of T_N with reduced particle size, indicating size dependent magnetic ordering.     

Confinement effects at nanoscale in natural rubber composites: Influence on macroscopic properties

The study of molecular level interactions in elastomer composites has got very scant attention even though a large number of studies are going on in this topic. This work embodies the understanding of confinement effects in natural rubber (NR)/ ZnO composites from micro to nano length scales, and their influence on macroscopic properties of the composites. The interactions between fillers and matrix are characterized from the Donth's approach, which allows estimating the cooperativity size N_α at the glass transition, N_α being directly related to the filler-matrix interactions. The improved properties of NR-nano ZnO composites can be attributed to microstructural and morphological changes due to nano ZnO in the NR matrix. A correlation between N_α, the constrained volume C_v and the thickness of immobilized polymer chains χ_m at the glass transition has also been established. Thus, this work proves that the Donth's approach is a powerful probe to estimate the enhance of mechanical properties in nanocomposites from calorimetric investigations.     

Simultaneous improvement in porosity and strength of porous β-Si3N4 ceramics by formation of ultrafine fibrous grains

Si₃N₄ ceramic with ultrafine fibrous grains are expected to exhibit remarkable mechanical properties. In this work, highly porous Si₃N₄ ceramic monoliths composed of ultrafine fibrous grains were developed via a novel vapor-solid carbothermal reduction nitridation (V-S CRN) reaction between SiO vapor and green bodies comprised of carbon nanotubes (CNTs), α-Si₃N₄ diluents and Y₂O₃ in a N₂ atmosphere. The unique fibrous grains-interconnected structure was developed through in-situ formation of Si₃N₄ and following liquid phase sintering. The porous Si₃N₄ monoliths with porosity of 61–78% was developed by controlling the contents of α-Si₃N₄ diluents and densities of the CNT green bodies. With increasing of the α-Si₃N₄ contents, Si₃N₄ fibrous grains with an aspect ratio of approximate or higher than 20 could be achieved, and the grains were gradually refined. For the samples with 40 wt% α-Si₃N₄, the minimum mean grain diameter and pore size of 164 nm and 0.79 μm were achieved, respectively, and the resultant porous Si₃N₄ monolith exhibited a flexural strength of as high as 73–102 MPa with the porosity of 61–73%, which is much higher than that of the reported in literature. The improvement of mechanical strength could be attributed to the densely interconnected bird's nests structure formed by the ultrafine fibrous grains. The effects of the α-Si₃N₄ diluents on the resulting porous Si₃N₄ monolith via this method were analyzed.     

Radical polymerization of fumaramide and fumaramate derivatives for homogeneous Langmuir monolayers

Summary The radical polymerization of a series of fumaramides and fumaramates, prepared from the reaction of various amines with fumaroyl dichloride and fumaric chloride isopropyl ester, respectively, was investigated. Although the polymerization reactivity of the N,N,N’,N’-tetrasubstituted fumaramides and N,N-disubstituted fumaramates was low, N-isopropyl fumaramate readily furnished the corresponding high molecular weight polymer. The highest number average molecular weight (M_n) of 15,400 was obtained from the emulsifier-free emulsion polymerization in the presence of VA-086 as the initiator. The decomposition temperature of the obtained polymer was determined to be 299 °C. The π-A isotherm of the polymer indicated the formation of stable Langmuir monolayers with a limiting molecular area (per macromolecular repeating unit) of ca. 26 ?².     

Glass transition temperatures of poly(alkyl α-cyanoacrylates)

The glass transition temperatures of the poly(alkyl α-cyanocrylates) were determined by the dilatometric technique, and some of the values were checked by differential thermal analysis. The data indicate that the T_g's appear to decrease with increase in the size of the alkyl group, for a given molecular weight range. It was also found that the T_g of poly(methyl or butyl α-cyanoacrylate) increased with molecular weight. All cyanoacrylates, excepting methyl and ethyl esters, formed only low molecular weight polymers in aqueous surroundings. Therefore, they have characteristic low glass transition temperatures, causing coalescence at low temperatures.     

Thermoelastic behavior of carbon fiber/polycarbonate model composites

Model composites of polycarbonate (PC) containing single, multiple and chopped carbon fibers (CF) with and without and epoxy sizing were prepared by hot pressing. The thermoelastic behavior of model CF/PC composites was characterized by stretching calorimetry at room temperature. For small strains ? (i.e., ? ≈ 0.01) the specific mechanical work, specific heat effects and specific internal energy changes ΔU were completely reversible in stretching/contraction cycles and quantitatively obeyed the standard relationships for elastic solids. Young's moduli E and ΔU were significantly higher, whereas the linear thermal expansivities α_L were lower for model CF/PC composites compared to those for the neat PC. Smaller values of the above parameters for composites reinforced with sized CF suggested weaker CF/PC interfacial interactions. Current theoretical models of thermoelastic properties of composite materials suggest the existence of unusually stiff, highly oriented PC structures in fairly thick boundary layers around CF. The onset of inelastic deformation, as well as mechanical failure in CF/PC model composites at significantly smaller strains compared to the neat PC were tentatively explained by the yield and subsequent plastic flow of the matrix polymer initiated by heat effects of fiber fragmentation processes, and by higher concentration of microvoids generated in fiber fragmentation/debonding events, respectively.     

Fatigue mechanism of fiber-reinforced polypropylene swollen by oil

Fatigue mechanism was investigated for the fiber-reinforced polypropylene (FRPP) swollen by a small amount of oil. The curves of applied cyclic stress (S) vs. logarithm of cycles to failure (N) shifted into smaller values of S and N, respectively, by adding oil into the polymer and with increasing a test temperature. The endurance limiting stress (σ_e) for the swollen FRPP, defined as the stress at a long lifetime, became much the same as the one for the swollen unfilled polypropylene, though the former was considerably larger than the latter for the breaking strength measured in standard bending test. The activation energy and the activated volume, which have been determined by the Eyring's model from the S–N curves at higher stress levels, suggest that the introduction of a small amount of oil into the polymer lowers a motional unit associated with a fatigue process from 30 to several repeat units. The major decrease in σ_e by swelling can be explained in terms of the crack–nucleation theory. It is indicated that this decrease yields from the change in the stress–concentration factor.     

New lipophilic cyclo- and poly-phosphazenes containing surfactant substituents

The reaction of the sodium salt of the commercially available surfactant Igepal CA 210^™ with hexachlorocyclotriphosphazene, N₃P₃Cl₆ (1) and poly(dichlorophosphazene), [—P(Cl₂)=N—]_n (Publisher's note: for graphical representation please see printed journal or the Acrobat PDF version on this website.) affords lipophilic cyclo- and poly-phosphazenes SSCP (2) and SSPP (4), respectively. These materials, containing a short chain oligo etheroxy side group while being completely insoluble in water, are soluble in a wide range of solvents ranging from hexane to chloroform. The polymer, SSPP (4) forms polymer–metal salt complexes with lithium salts. DC conductivity measurements by a complex impedance method have been carried out. The maximum conductivity observed for SSPP–LiClO₄ (O: Li ratio, 6:1) is 1·0×10^-6Scm^-1 at 348K. © 1998 SCI.     

Preparation,Crystal Structure,Thermal Decomposition,and Explosive Properties of [Cd(en)(N3)2]n

A new multi‐ligand coordination polymer of cadmium(II) ethylenediamine azide, [Cd(en)(N₃)₂]_n (en=ethylenediamine), was synthesized and characterized by using elemental analysis and FT‐IR spectrum. Its crystal structure was determined by means of X‐ray single crystal diffraction. The obtained results show that this crystal belongs to monoclinic, P2₁/n space group, a=0.6548(1) nm, b=1.0170(2) nm, c=1.2246(2) nm, β=90.23(1)°, V=0.8156(2) nm³, D_c=2.090 g⋅cm⁻³, Z=4, R₁=0.024, wR₂ (I>2σ(I))=0.0416 and S=0.998. The Cd(II) ion is six‐coordinated with four azido ligands by μ‐1, 1 azido bridges, and two ethylenediamine molecules which serve as bidentate ligands through the nitrogen atoms. The thermal decomposition mechanism of the title complex was studied by using differential scanning calorimetry (DSC) and thermogravimetry‐differential thermogravimetry (TG–DTG) techniques. Under nitrogen atmosphere with a heating rate of 10 K⋅min⁻¹, the thermal decomposition of the complex contains two main successive exothermic processes between 519 and 701 K in the DSC curve, and the final decomposed residue at 725 K is Cd. The non‐isothermal kinetics parameters were calculated by using the Kissinger's method, Ozawa–Doyle's method, pervasive integration method, and differential method, respectively. The sensitivity properties of [Cd(en)(N₃)₂]_n were also determined with standard methods.     

Atomistic molecular dynamics simulations of gas diffusion and solubility in rubbery amorphous hydrocarbon polymers

Diffusion coefficients D of H₂, He, O₂, N₂, and CO₂ in different rubbery amorphous polymeric matrices were estimated by atomistic molecular dynamics simulations at 298 K using the Einstein relationship, and compared with the relevant experimental values, where available. The simulated diffusion coefficients D of all the gases in all polymers considered almost regularly decreased with increasing molecular gas volumes and increasing polymer glass transition temperature. Further, solubility coefficients and heats of solution were obtained for all gases from Grand Canonical Monte Carlo simulations, which were also used to calculate sorption isotherms. In general, there is a good agreement between experimental and simulated values of diffusion and solubility coefficients for all gases considered.     

Effect of graft modification with poly(N‐vinylpyrrolidone) on thermal and mechanical properties of poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

Poly(N‐vinylpyrrolidone) (PVP) groups were grafted onto poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) backbone to modify the properties of PHBV and synthesize a new novel biocompatible graft copolymer. The effect of graft modification with PVP on the thermal and mechanical properties of PHBV was investigated. The thermal stability of grafted PHBV was remarkably improved while the melting temperature (T_m) was almost not affected by graft modification. The isothermal crystallization behavior of samples was observed by polarized optical microscopy and the results showed that the spherulitic radial growth rates (G) of grafted PHBV at the same crystallization temperature (T_c) decreased with increasing graft yield (graft%) of samples. Analysis of isothermal crystallization kinetics showed that both the surface free energy (σ_e) and the work of chain‐folding per molecular fold (q) of grafted PHBV increased with increasing graft%, implying that the chains of grafted PHBV are less flexible than ungrafted PHBV. This conclusion was in agreement with the mechanical testing results. The Young's modulus of grafted PHBV increased while the elongation decreased with increasing graft%. The hydrophilicity of polymer films was also investigated by the water contact angle measurement and the results revealed that the hydrophilicity of grafted PHBV was enhanced. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis,characterization and thermal degradation of dual temperature‐ and pH‐sensitive RAFT‐made copolymers of N,N‐(dimethylamino)ethyl methacrylate and methyl methacrylate

Poly{[(N,N‐(dimethylamino)ethyl methacrylate]‐co‐(methyl methacrylate)} copolymers of various compositions were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization at 70 °C in N,N‐dimethylformamide. The polymer molecular weights and molecular weight distributions were obtained from size exclusion chromatography, and they indicated the controlled nature of the RAFT polymerizations; the polydispersity indices are in the range 1.1–1.3. The reactivity ratios of N,N‐(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA) (r_DMAEMA = 0.925 and r_MMA = 0.854) were computed by the extended Kelen–Tüdös method at high conversions, using compositions obtained from ¹H NMR. The pH‐ and temperature‐sensitive behaviour were studied in aqueous solution to confirm dual responsiveness of these copolymers. The thermal properties of the copolymers with various compositions were investigated by differential scanning calorimetry and thermogravimetric analysis. The kinetics of thermal degradation were determined by Friedmann and Chang techniques to evaluate various parameters such as the activation energy, the order and the frequency factor. © 2012 Society of Chemical Industry     

New soluble cyano‐containing poly(arylene ether) copolymers bearing pendant xanthene groups

Homopolymers and copolymers of poly(arylene ether nitrile) (PAEN)‐bearing pendant xanthene groups were prepared by the nucleophilic substitution reaction of 2,6‐difluorobenzonitrile with 9,9‐bis(4‐hydroxyphenyl)xanthene (BHPX) and with various molar proportions of BHPX to hydroquinone (100/0 to 40/60) with N‐methyl‐2‐pyrrolidone (NMP) as a solvent in the presence of anhydrous potassium carbonate. These polymers had inherent viscosities between 0.61 and 1.08 dL/g, and their weight‐average molecular weights and number‐average molecular weights were in the ranges 34,200–40,800 and 17,800–20,200, respectively. All of the PAENs were amorphous and were soluble in dipolar aprotic solvents, including NMP, N,N‐dimethylformamide, and N,N‐dimethylacetamide and even in tetrahydrofuran and chloroform at room temperature. The resulting polymers showed glass‐transition temperatures (T_g's) between 220 and 257°C, and the T_g values of the copolymers were found to increase with increasing BHPX unit content in the polymer. Thermogravimetric studies showed that all of the polymers were stable up to 422°C with 10% weight loss temperatures ranging from 467 to 483°C and char yields of 54–64% at 700°C in nitrogen. All of the new PAENs could be cast into transparent, strong, and flexible films with tensile strengths of 106–123 MPa, elongations at break of 13–17%, and tensile moduli of 3.2–3.7 GPa. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal and mechanical properties of plasticized poly(L‐lactic acid)

Acetyl tri‐n‐butyl citrate (ATBC) and poly(ethyleneglycol)s (PEGs) with different molecular weights (from 400 to 10000) were used in this study to plasticize poly(L‐lactic acid) (PLA). The thermal and mechanical properties of the plasticized polymer are reported. Both ATBC and PEG are effective in lowering the glass transition (T_g) of PLA up to a given concentration, where the plasticizer reaches its solubility limit in the polymer (50 wt % in the case of ATBC; 15–30 wt %, depending on molecular weight, in the case of PEG). The range of applicability of PEGs as PLA plasticizers is given in terms of PEG molecular weight and concentration. The mechanical properties of plasticized PLA change with increasing plasticizer concentration. In all PLA/plasticizer systems investigated, when the blend T_g approaches room temperature, a stepwise change in the mechanical properties of the system is observed. The elongation at break drastically increases, whereas tensile strength and modulus decrease. This behavior occurs at a plasticizer concentration that depends on the T_g‐depressing efficiency of the plasticizer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1731–1738, 2003     

Design,synthesis and characterization of semi‐conducting interpenetrating polymer network (IPN) of pyridine and poly(antimony acrylate)

A new series of semi‐conducting interpenetrating polymer networks (IPNs) based on pyridine and poly(antimony acrylate) were synthesized. Structural evidence for IPNs come from the infrared spectra indicating characteristic frequencies of (>C = O) of poly(antimony acrylate) at 1680 cm^?1. Properties such as percentage swelling, average molecular weight between crosslinks (M_c) and Young's modulus are direct functions of the concentration of linear polymer and initiator (benzoyl peroxide), whereas inverse relationships with concentration of monomer (pyridine) and crosslinker (divinyl benzene) are observed. The presence of antimony in the IPNs is determined by SEM and elementac analysis. The DSC curve shows two glass transition temperatures (T_g), at 110 and 150 °C. The IPNs formed with a low content of pyridine exhibited processability, mechanical properties and conductivity. © 2003 Society of Chemical Industry     

Synthesis of dextran‐metaxalone conjugates and study on their control drug release behaviors

Metaxalone (Met), a drug for treatment of pain and stiffness due to muscle injuries, was covalently linked to dextran via a chloroacetyl chloride spacer. The average molecular weights of dextran are 20,000 (D₂₀₀₀₀) and 40,000 (D₄₀₀₀₀), respectively, and the procedure of chemical modification for dextrans was conducted by a two‐step protocol: (1) synthesis of N‐chloroacetyl‐metaxalone; (2) synthesis of D₂₀₀₀₀‐Met and D₄₀₀₀₀‐Met. The controlled drug release studies were performed in buffer solutions with pH values of 1.1, 7.4, and 10.0. The results demonstrate that, under the same condition, the rate of release for D₂₀₀₀₀‐Met is slower than that of D₄₀₀₀₀‐Met, and more amount of Met can be detected releasing from polymer‐drug conjugate at the presence of α‐chymotrypsin in a buffer solution with pH = 8.0. It was also found that these novel polymer‐drug conjugates can effectively improve the Met's pharmacokinetics, and can increase its half‐life period. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polymer swelling. XXIII. Molecular structure–affinity correlation studies involving poly(styrene-co-divinylbenzene) exposed to acyclic olefinic liquids

The adsorption parameters (α) of 45 olefinic liquids with respect to poly(styrene-co-divinylbenzene) were established gravimetrically in the usual way. Those for the structures that comprise R_aR_bCCR_cR_d, where each R is H or an alkyl group, can be fitted to log α_f = log α_i − D_s(N_f − N_i) relationships, where N_i and N_f are the initial and final number of mass units in the subseries of the above general molecular structure (GMS). The constant α_i reflects the number of methyl groups in lieu of H atoms and their positional relationship to each other on the double bond, whereas the constant D_s reflects the unit change in log α_i caused by incrementation of a (CH₂)_nR substituent from n = 1 to its allowable limit while the rest of the molecular structure is kept constant. The results observed thereby confirm that these adsorption phenomena involve a liaison between the pendent phenyl groups of the sorbent polymer and the double bond of the sorbate liquid. The adsorption data accumulated in these studies show that in the cases of olefinic liquids carrying other kinds of functional groups, such as aromatic or ether groups, the adsorption preference usually favors the other functionality, leaving the olefinic group in the “nonadsorbed” portion of the adsorbed molecule where it can exert a positive influence on adsorptivity due to dynamic associative interactions with the mobile sorbed molecules of its own kind. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1583–1609, 1999