Influence of Polymer Coated CaCO3 on Vulcanization Kinetics of Natural Rubber/Sulfur/N-Oxydiethyl Benzthiazyl Sulfenamide (BSM) System

The effect of polymethyl methacrylate (PMMA)-encapsulated calcium carbonate on the kinetics of the vulcanization of natural rubber (NR) with a vulcanizing agent (sulfur) accelerated by N-oxydiethyl benzthiazyl sulfenamide (BSM) has been studied. The PMMA coating (4% by weight of CaCO₃) was prepared by dispersion polymerization, and compositions of five NR composites were 10, 15, 20 phr of treated CaCO₃ and 20 and 40 phr of untreated CaCO₃. The vulcanization kinetics was determined by oscillating disc rheometry (ODR) and the kinetic parameters were determined by the model equations. The kinetic analysis suggests that the two-parameter auto catalytic model is the more appropriate one to elucidate the kinetics of the vulcanizing reaction of the present system. These parameters support the nature of the experimental ODR curves (degree of conversion–time plots). The encapsulated CaCO₃ leads to a change in vulcanization reaction and has an effect on the kinetic parameters E, ln K₀, m and n, and consequently on the overall reactivity.     

Structural characterization of vulcanized natural rubber by latex state 13C NMR spectroscopy

Structural characterization of vulcanized natural rubber was performed by high‐resolution latex‐state ¹³C NMR spectroscopy. The vulcanized natural rubber latex was prepared by vulcanization of high ammonia natural rubber latex with sulfur and sodium di‐n‐butyldithiocarbamate as vulcanizing agents. High resolution was attained for latex‐state ¹³C NMR spectroscopy even after vulcanization of the rubber latex, as is evident from no background in spectrum and narrow half width of signals, which were independent of vulcanization time. Small signals at 44 and 58 ppm in the carbon region were assigned by measurements of both distortionless enhancement by polarization transfer (DEPT) and attached proton test (APT) to secondary, tertiary, and quaternary carbons of crosslinking points. The assignment was proved by high‐resolution solution‐state NMR spectroscopy of vulcanized liquid cis‐1,4‐polyisoprene as a model, in which DEPT, APT, 2‐dimensional ¹H‐¹³C correlation (HETCOR), and 2‐dimensional heteronuclear multiple bond correlation (HMBC) measurements were applied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1003–1009, 2007     

Effects of cellulose nanocrystals on the vulcanization of natural rubber/cellulose nanocrystals nanocomposite and corresponding regulating strategies

Vulcanization is a vital process in rubber processing, it endows rubber with valuable physical and mechanical properties, making rubber a widely used engineering material. In addition to vulcanization agent, reinforcing fillers play a non-ignorable influence on the vulcanization of rubber nanocomposites. Herein, the effects of cellulose nanocrystals (CNCs) on the vulcanization of natural rubber (NR)/CNCs nanocomposite was studied. It was found that even though the addition of CNCs can effectively improve the dispersion of ZnO in NR matrix, the vulcanization of NR was inhibited. This may be attributed to the CNCs' adsorption of vulcanizing agents (DM, ZnO) and the acidic chemical environment on the surface of CNCs. In order to improve the vulcanization properties of NR/CNCs nanocomposite, tetramethyldithiochloram (TMTD) and triethanolamine (TEOA) were used as a combination accelerator and curing activator, respectively, and polyethylene glycol (PEG) was introduced to screen hydroxyl groups on the surface of CNCs to prohibit the CNCs' adsorption of vulcanizing agents. The results indicate that TMTD and TEOA effectively improved the vulcanization rate of NR/CNCs nanocomposite and increased the crosslink density by an order of magnitude. Subsequently, the tensile strength, tear strength, and so forth. of NR/CNCs nanocomposite were significantly improved. However, PEG hardly help to improve the vulcanization properties of NR/CNCs nanocomposite. In addition, the control samples without CNCs were prepared and characterized, the comparation between NR and NR/CNCs nanocomposite shows that the synergistic effect of crosslink density and CNCs' reinforcement more effectively improve mechanical properties of NR. This work not only elucidates the inhibiting mechanisms of CNCs on the vulcanization of NR, but also provides practical strategies for improving the vulcanization and properties of NR/CNCs nanocomposite. It may accelerate the application of CNCs as rubber reinforcing filler.     

Michael addition for crosslinking of poly(caprolactone)s

Poly(caprolactone) (PCL) networks have received significant attention in the literature because of many emerging potential applications as biodegradable materials. In this study, the Michael addition reaction was used for the first time to synthesize biodegradable networks using crosslinking of acetoacetate‐functionalized PCL (PCL bisAcAc) oligomers with neopentyl glycol diacrylate. Hydroxyl‐terminated PCL telechelic oligomers with number‐average molecular weights ranging from 1000 to 4000 g/mol were quantitatively functionalized with acetoacetate groups using transacetoacetylation. In addition to difunctional PCL oligomers, hydroxyl‐terminated trifunctional star‐shaped PCL oligomers were functionalized with acetoacetate groups. Derivatization of the terminal hydroxyl groups with acetoacetate groups was confirmed using FTIR spectroscopy, ¹H NMR spectroscopy, mass spectrometry, and base titration of hydroxyl end groups. PCL bisAcAc precursors were reacted with neopentyl glycol diacrylate in the presence of an organic base at room temperature. The crosslinking reactions yielded networks with high gel contents (>85%). The thermomechanical properties of the networks were analyzed to investigate the influence of molecular weight between crosslink points. The glass transition and the extent of crystallinity of the PCL networks were dependent on the molecular weight of the PCL segment. Dynamic mechanical analysis indicated that the plateau modulus of the networks was dependent on the molecular weight of PCL, which was related to the crosslink density of the networks. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5437–5447, 2009     

Relationship between the Physicochemical Properties of Electrolytes and the Electronic Structure of Solvated Alkali Metal Cations

Group theoretical analysis and linear combinations of molecular orbitals of the cation and solvent are used to establish the nature and stability of bonds and hence the electric mobility of the cation and the viscosity of the electrolyte depending on the type of cation (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and molecules (H₂O, NH₃, H₂CO, (CH₃)₂CO, CH₃CN). Solvation effects on the UV photoelectron and intramolecular vibrational IR and NMR spectra are revealed.     

Thermal,viscoelastic, and mechanical properties of DCPD-containing polymers

The thermal, viscoelastic, and mechanical properties of cured dicyclopentadiene (DCPD)-containing polymers prepared from novel DCPD-modified unsaturated epoxypolyesters and styrene were evaluated. This was accomplished using thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, three-point bending test, and Brinell’s hardness. The thermal, viscoelastic, and mechanical properties of DCPD-containing polymers were strongly dependent on chemical structure. The cross-linking density (υ _e) of obtained networks increased with increasing content of carbon–carbon double bonds in the poly(ester) structure. In addition, the introduction of DCPD rings into the poly(ester) structure increased the rigidity of the molecular backbone. It resulted in obtaining polymers which showed great improvement in mechanical properties including remarkably higher storage modulus ( E_{20 ^°\textC}^￠ E_{{20\,{}^{\circ}{\text{C}}}}^{'} ), flexural modulus at bending (E _mod), hardness, lower extension at maximum force (ε-F _max), as well as higher thermal stability. These good properties make these materials highly promising as potential candidates for structural applications.     

Effect of metal type on the metallocene-catalyzed oligomerization of 1-hexene and 1-octene to produce polyα-olefin-based synthetic lubricants

1-Hexene and 1-octene oligomerization reactions were performed with Cp₂ZrCl₂ and Cp₂HfCl₂ in the presence of methylaluminoxane as cocatalyst at 25 and 80 °C to produce polyα-olefin-type oils. By examining the molecular weight results, obtained from gel permeation chromatography, the oligomeric structure of the products was confirmed. Hafnocene produced oligomers with higher molecular weights in comparison with zirconocene under the same reaction condition. In addition, with increasing temperature, the molecular weight decreased. Differential scanning calorimetry analysis of the poly1-hexene- and poly1-octene-type oligomers confirmed their amorphous nature. ¹H-nuclear magnetic resonance (NMR) analysis was performed to study the mechanism of termination reactions. The results obtained from the ¹H-NMR analysis confirmed the vinylidine form (vd) as the only unsaturated structure in all synthesized oligomers. Therefore, in the 1-hexene and 1-octene oligomerization reactions with these two catalytic systems, the chain termination is totally accomplished by β-hydride elimination at both reaction temperatures.     

Molecular-mass-distribution of oligomers in the products of tetrafluoroethylene telomerization in various solvents

The possibility of using differential thermogravimetry (DTG) for determination of the molecularmass-distribution (MMD) of oligomers in polymerization products has been experimentally and theoretically substantiated. The technique is based on the assumptions that the increase in the boiling temperature of oligomers with the increasing chain length is described by the additivity rule and the shape of DTG curves obeys the equation of mass transfer in the stationary convective flow created by evaporation. The results have been confirmed by gel-permeation chromatography and ¹⁹F NMR data. It has been shown that the chain length of oligomers produced via tetrafluoroethylene (TFE) telomerization in carbon tetrachloride, chloroform, acetone, and ethyl acetate reaches about 20–25 C₂F₄ units at an initial TFE concentration of C ₀ ≈ 0.5 mol/l. The MMD includes a low-molecular-mass component (n ≤ 5) in an amount that decreases with increasing C ₀ and a high-molecular-mass component, whose maximum shifts toward higher values of n with an increase in C ₀. The bimodality of MMD is explained in terms of decrease in the propagation rate constant with the accumulation of long oligomers.     

Preparation and ionic conductivity of poly(ethylene oxide) oligomers having thiolate groups on the chain ends

Poly(ethylene oxide) (PEO) oligomers having alkali metal thiolate groups on the chain ends (PEO _m -S⁻M⁺) were prepared as an ion conductive matrix. The molecular weight of the PEO part (m) and the content of the thiolate groups in the molecule were changed to analyze the effect of carrier ion concentration in the bulk. In a series of potassium salt derivatives, PEO₃₅₀-SK showed the highest ionic conductivity of 6.42 × 10⁻⁵ S/cm at 50 °C. In spite of a poor degree of dissociation which was derived from the acidity of the thiolate groups, PEO _m -SM showed quite high ionic conductivity among other PEO/salt hybrids. PEO _m -SM had glass transition temperatures (T _g) 20 °C lower than other PEO/salt hybrids. Lowering the T _g was concluded to be effective in providing higher ionic conductivity for PEO-based polymer electrolytes. Received: 30 April 1999 / Accepted: 20 June 1999     

Ethylenediamine and 1,10-phenanthroline biscyclometallated complexes of Pd(II) and Pt(II) based on 4,6-diphenylpyrimidine

Biscyclometallated [(M(N∧N))₂(μ-dphpm)](ClO₄)₂ and [(N∧N)Pd(μ-dphpm)Pt(N∧N)]Cl₂ complexes [M = Pd(II), Pt(II); (N∧N) ethylenediamine (En), 1,10-phenanthroline (phen); dphpm² — bisdeprotonated form of 4,6-diphenylpyrimidine)] have been characterized by the ¹H NMR, electronic absorption and emission spectroscopy, and also cyclic voltammetry methods. The lowest unoccupied molecular orbital (LUMO) of biscyclometallated complexes with ethylenediamine, responsible for low-energy photo- and electro-stimulated processes irrespective of the metal nature, is assigned to the π* orbital mainly localized on the pyrimidine part of the bridging ligand. In the case of complexes with phenanthroline chelating ligands, the replacement of one or two palladium metal centers [{Pd(phen)}₂(μ-dphpm)]²⁺ by platinum centers changes the LUMO nature of the complexes for the π* orbital mainly localized on the peripheral metal-complex fragment {Pt(phen)}.     

Polymorphism for a novel phosphoramidate; NMR and X-ray crystallography

Abstract  

New phosphoramidates with formula 3-NC₅H₄C(O)NHP(O)XY (X=Y=Cl (1), X=Y=NH–C(CH₃)₃ (2a,2b), X=Y=N(C₄H₉)₂ (3), X=Cl, Y=N(C₂H₅)₂ (4) were synthesized and characterized by IR, ¹H-, ¹³C-, ³¹P-NMR spectroscopy and CHN elemental analysis. Surprisingly, the reaction of compound 2a with LaCl₃, 7H₂O in 3:1 M ratio leads to a polymorph of this compound (2b). NMR spectra indicate that ² J(PNH_amide) in 2b (7.0 Hz) is very much greater than in 2a (4.1 Hz), while δ(³¹P) values are identical for both of them. In IR spectra, υ(P=O) is weaker but υ(C=O) is stronger in 2a than in 2b. The structures of 2a, 2b were determined by X-ray crystallography. These compounds form centrosymmetric dimers via two intermolecular P=O……H–N hydrogen bonds. Strong intermolecular N–H…N, N–H…O and weak C–H…O hydrogen bonds lead to a three-dimensional polymeric cluster in the 2a while intermolecular strong N–H……N and weak C–H……O hydrogen bonds form a two-dimensional polymeric chain in 2b.     

2-Arylazo-1-vinylpyrroles: oligomerization in the presence of protic and aprotic acids

2-Arylazo-1-vinylpyrroles react with protic (CF₃COOH, HCl) and aprotic (BF₃) acids forming deeply colored oligomeric products consisting of soluble (in benzene, chloroform) and insoluble fractions with yields amounting to 73 %. According to the data from ¹H NMR and IR spectroscopy oligomerization takes place mainly at the 1-vinyl group with partial involvement of the pyrrole ring. The process is accompanied by capture of the catalyzing acids by the azo group, leading to strong polarization of the elementary unit with transfer of positive charge to the pyrrole ring, which thus becomes capable of further transformations with cross-linking of oligomeric chains. The obtained oligomers possess electric conductivity of 10⁻¹³-10⁻⁹ S/cm, which is increased to 4.8∙10⁻⁶ S/cm when the products are iodinated with iodine vapor.     

Polyfunctional complex sulfur-containing additives to SKI-3 rubber and vulcanizates thereof

The performance of new polyfunctional additives containing bis(2,6-di-tert-butyl-4-hydroxyphenyl) polysulfide and dicyclopentadiene-sulfur copolymer was studied with respect to SKI-3 and vulcanizates thereof. These additives act not only as stabilizers but also as vulcanizing agents improving a number of physicomechanical characteristics of the vulcanizates.     

Cation mobility in modified Li1 ? xTi2 ? xNbx(PO4)3 lithium titanium NASICON phosphates

Li_{1 − x} Ti_{2 − x} Nb _x (PO₄)₃ NASICON materials are prepared and studied by X-ray diffraction, ⁷Li and ³¹P NMR spectroscopy, and impedance spectroscopy. Vacancy mobility in Li_{1 − x} Ti_{2 − x} Nb _x (PO₄)₃ is lower than interstitial lithium mobility. Nb⁵⁺ cations with low doping levels increase cation mobility in LiTi₂(PO₄)₃. Original Russian Text ? I.Yu. Pinus, I.A. Stenina, A.I. Rebrov, N.A. Zhuravlev, A.B. Yaroslavtsev, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 8, pp. 1240–1244.     

Synthesis,characterization, and ring-opening polymerization of novel high Tg macrocyclic oligomers based on 1,2-dihydro-4-(4-hydroxyphenyl)(2H)- phthalazin-1-one

Preparation of novel high T_g (220–280°C) macrocyclic oligomers in high yield by the reaction of 1,2-dihydro-4-(4-hydroxyphenyl)(2H)phthalazin-1-one with activated difluoro-monomers is described. The reaction, conducted under pseudo-high dilution conditions, produces cyclic oligomers in 90–97% isolated yield. Detailed structural characterization of these novel oligomers by the combination of NMR, MALDI–TOF–MS, GPC, and reverse-phase HPLC confirm the cyclic nature and reveal the composition of these cyclic oligomers. MALDI–TOF–MS which enables the detection of oligomers with mass up to 6000 Da, is shown to be a very powerful tool for determination of and the proof of the cyclic nature of the cyclic oligomers. The MALDI results provide answers to the possible combinations of monomer units in the cyclic oligomeric components for random co-cyclic oligomers. Rheological measurement of cyclic oligomers 3c shows that the cyclic oligomers are thermally stable in the melt and the molten cyclic oligomers essentially behave like Newtonian fluids. At 340°C and 100 s⁻¹ the steady-state shear viscosity of the molten cyclic oligomers 3c is only about 14 poise. Ring-opening polymerization of the co-cyclic oligomers 4 to a high molecular weight polymer with M_w = 87,000 is achieved by heating at 340°C for 45 min in the presence of a nucleophilic initiator. © 1996 John Wiley & Sons, Inc.     

nBody democratic recoupling and role of Schur Fn. products on Sn, a NMR dual-group view pertinent to coherence-transfer

For automorphic spin symmetries over isotopomer networks defining both NMR coherence transfer and cage-cluster ro-vibrational (RV) weighting phenomena, the role of Schur functions (SF) and their SF products (SFP) (restricted to S_n) is re-evaluated, beyond that typical of atomic physics. It is seen now as being equally applicable to molecular physics. Our special focus here is on the SU2 × S_n dual group for its importance in replacing (Jucys) recoupling schemata by generalised S_n democracy invariants, which ensure the retention of simple reducibility (SR) of carrier spaces for superboson mappings, under U × P(Γ) actions over Liouville space, i.e., as in Physica A 198 (1993) 245. SFP mapping onto S_n and simple Young rule SF mappings onto {[λ]}(S_n) sets are developed in the high n-index, weak-branching limit and utilise known similarities in the algorithms for the Young and Littlewood–Richardson rules. Over discrete k rank, from k=n (down), the Σ_ν{/T ^k(ν)/x007D;k-set orders are related to the ⊵ ordered bipartite χ _12n ^[λ] (S _2n characters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physical investigation of the colloidal iron-inulin complex

The iron-inulin complex, which could be applied as a parenteral hematinic agent, is studied by physical techniques. Electron microscopy shows that the complex contains very small particles that are approximately spherical and 10–30 nm in diameter. The examination reveals the presence of an electron-transparent sheath, probably consisting of linked inulin oligomers with M _w ∼ 3000 g mol⁻¹, around the electron-dense, ironcontaining core of the FeOOH particles. FTIR spectroscopy suggests the existence of stronger hydrogen bonds, which are formed in the complexes between FeOOH and oligosaccharides, compared to the hydrogen bond in the initial compounds. A gel filtration technique on a Sephadex column showed conclusively that a large proportion of combined inulin oligomers with M _w ∼ 1500 g mol⁻¹ as secondary fractions are present in complexes. These low-molecular-weight inulin fractions have a significant influence on the complex stability. The text was submitted by the authors in English.     

Mobile ion transport pathways in (LiBr) x [(Li2O)0.6(P2O5)0.4](1−x) glasses

(LiBr) _x [(Li₂O)_0.6(P₂O₅)_0.4]_{(1 − x)} glasses with 0 ≤ x ≤ 0.2 are prepared by melt quenching. Glass transition temperature (T _g), ionic conductivity (σ), and its activation energy (E _a) are determined experimentally and correlated to molecular dynamics (MD) simulations with an optimized potential, fitted to match bond lengths, coordination numbers, and ionic conductivity. Based on equilibrated MD configurations, ion transport pathways are modelled in detail by the bond valence approach to clarify the influence of the halide dopant concentration on the glass structure and its consequence for Li ion mobility. Results of experimental and computational studies are compared with our previous report on the (LiCl) _x [(Li₂O)_0.6(P₂O₅)_0.4]_{(1 − x)} system. Both T _g and σ values are higher for LiBr-doped glasses than for LiCl-doped glasses, but the effect of halide doping is unusually small.     

Solvent effect on the photogeneration of singlet molecular oxygen by copper tetra(tert-butyl)phthalocyanine

The photogeneration of the singlet molecular oxygen (¹O₂) by copper tetra(4-tert-butyl) phthalocyanine in organic solvents of different nature was substantiated. The apparent quantum yields of ¹O₂in benzene and pyridine were determined. The data obtained indicate an influence of the coordinating properties of the solvent on the ¹O₂yield. However, this factor is not “critical” as in the case of photogeneration of ¹O₂by copper tetra(5-tert-butylpyrazino)porphyrazine.