Preparation,characterization and thermal degradation study of poly(amide imide)s based on tri-component mixture of PMDA/BTDA,diamines and acid chloride

A series of poly(amide imide)s (PAIs) having alternate (amide–amide) and (imide–imide) units (polymers 1–14 and 22–35), and random distribution of amide-imide linkages (polymers 15–21 and 36–42) were prepared by low temperature solution polymerization of benzene-1,2,4,5-tetracarboxylic dianhydride (PMDA)/benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA), diamines (cyclic and aromatic) and acid chloride in dimethylforamide. All the polymers were readily soluble in polar aprotic solvents with inherent viscosities in the range of 0.134–0.878. The process of cycloimidization of poly(amide amic acid)s (PAAs) to PAIs was investigated by TGA and FT-IR techniques at four different temperatures i.e., 175, 200, 225, and 260 °C. The rate of cycloimidization was calculated by taking into account the theoretical weight loss (W_T), obtained from [n × M_w (H₂O)/M_w (R_U)] W, where M_w (H₂O) molecular weight of water, W weight of PAA taken for TGA, M_w (R_U) the molecular weight of repeat unit of PAA, n number of water molecules eliminated per repeat unit of PAA upon cycloimidization. For a particular diamine, the extent of percentage cycloimidization at the end of the isothermal heating was higher for PAAs containing trimellitic anhydride chloride (TMAc) unit, irrespective of the nature of the dianhydride and diamine. Thermal and thermooxidative degradation of PAIs was investigated by TGA in nitrogen and oxygen atmosphere. The initial decomposition temperatures (IDT) of polymers are above 260 °C, and vary widely (from 260 to 501 °C) depending upon the structure of the polymer backbone. PAIs containing TMAc exhibited higher thermal stability as compared to those polymers having diacid chloride units, in both N₂/O₂ atmospheres.     

Synthesis, characterization, and ethylene polymerization behavior of [(RR′-admpzp)2Ti(OPr)2] complexes (RR′-admpzp = 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-olate)

[(RR′-admpzp)₂Ti(OPrⁱ)₂] complexes (2a-c), synthesized from reaction of Ti(OPrⁱ)₃Cl (0.5 equiv) with 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-ol compounds in the presence of triethylamine (0.5 equiv), are pseudo-octahedral with each RR′-admpzp ligand κ²-O,N(pyrazolyl) coordinated to the titanium center. In solution, 2a-c adopt isomeric structures that are in dynamic equilibrium. At 23 °C, 2a-c/1000 MAO catalyst systems furnished high molecular weight polymers with narrow molecular weight distributions (M_w/M_n = 2.7-2.8). At 100 °C, 2a-c/MAO catalyst systems exhibited increased polymerization activity and 2c/1000 MAO system furnished high molecular weight polyethylene with a molecular weight distribution (M_w/M_n = 2.1) that is close to that found for single-site catalysts.     

Control of molecular weight distribution in polycondensation polymers 2. Poly(ether ketone) synthesis

Synthesis of aromatic poly(ether ketone) (3) with a narrow molecular weight distribution (M_w/M_n) was investigated via polycondensation. M_ns of 3 could be controlled varying the feed ratio of monomer (1) and initiator (2) maintaining relatively narrow M_w/M_ns (<1.3). The kinetics of polycondensation obeyed a first-order relationship between polycondensation time and -(1/[2]₀) ln([1]/[1]₀), and the rate of polycondensation was estimated as 2.57 mol⁻¹ L h⁻¹. MALDI-TOF mass analysis of 3 indicated that polycondensation should proceed via chain growth manner to give 3 having an initiator unit in each chain end.     

Calculations of Jahn-Teller coupling constants in the weak-field basis via the angular overlap model: a simple operator equivalent technique

Within the framework of the angular overlap model the matrix elements of the linear Jahn-Teller operator may easily be calculated in the weak-field basis in terms of simple operator equivalents. The method is applied to the calculation of the 〈M_J|?V/?Q|M_j〉 matrix elements for the |LSJMj〉 ground states of t^x species (x = 1) ? 13) in )^* symmetry.     

Synthesis and crystal structure of mixed metal(III) tungstenyl(VI) ortho-pyrophosphates

The series of isotypic anhydrous ortho-pyrophosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, V, Cr, Fe, Mo, Ru, Rh, In, Ir) was obtained via vapor phase moderated solid state reactions in sealed ampoules. The crystal structure of the phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: V, Ru, Rh) was solved from single crystal X-ray data (C2/c, Z = 16). Fairly regular MO₆ and distorted WO₆ octahedra share vertices with PO₄ and P₂O₇ units to form a 3D network. For the ortho-pyrophosphates with M: V³⁺, Cr³⁺, and Fe³⁺ the oxidation state of M is confirmed by magnetic measurements. ³¹P-MAS-NMR spectra of the diamagnetic phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, In, Ir) show surprisingly different isotropic chemical shifts for the seven phosphorus sites. V^III(W^VIO₂)₂(P₂O₇)(PO₄) occurs as equilibrium phase in the quasi-binary system (V_1–xW_x)OPO₄ at x = 0.67 and exhibits a small homogeneity range 0.60 ≤ x ≤ 0.67. The scandium compound shows a fully inverted occupancy of the M sites according to the formulation W(Sc_1/2W_1/2O₂)₂(P₂O₇)(PO₄).     

Phase relations in the dioxide-trioxide region of some 3d transition Metal-WO ternary systems

The phases occurring in the MnWO, FeWO, CoWO, and NiWO systems at 1373°K have been determined using X-ray diffraction and electron and optical microscopy. Experimentally most attention was given to the MnWO system, where it was found that Mn entered as the Mn²⁺ ion into the WO₃ host matrix and formed a perovskite-related bronze Mn_xWO₃. The highest observed x-value in the bronze is about 0.027. In addition a metastable θ_w(Mn) oxide with the Mo₅O₁₄ structure and a disordered oxide of overall composition approximately (Mn, W)O_2.82 were found. The FeWO system was similar to the MnWO system but significant differences occurred in the CoWO and NiWO systems where M_xWO₃ bronze phases were not observed to form at 1373°K. The stability of the M_xWO₃ and the θ_w(M) oxides formed are discussed in terms of the ionic size of the M ions involved. It is suggested that M_xWO₃ bronzes are metastable if these M ions are small.     

NMR, potentiometric and ESI-MS combined studies on the zinc(II) magnesium(II) and calcium(II) complexation by (morpholin-1-yl)methane-1,1-diphosphonic acid and its thio-analog

The crystal structures of the two derivatives of aminomethane-1,1-diphosphonic acid with morpholinyl- (1) and thiomorpholinyl- (2) side chains were determined by single crystal X-ray diffraction and discussed with respect to molecular geometry and solid state organization. The protonation equilibria, solution behavior and complex-formation equilibria in solutions of 1 and 2 with the Zn(II), Mg(II) and Ca(II) ions were studied by means of NMR, pH-potentiometry and ESI-MS methods.As the pK_(NH⁺) protonation constants of 1 and 2 are high (11.65 and 11.91, respectively) two different approaches were used to evaluate the pH-potentiometric data. The first approach disregarded the proton-dissociation from the NH⁺ group. In the second one, all the pK_a values were considered in the M(II):ligand formation equilibria. For 1, the accuracy of the pK_(NH⁺) determination was shown to be sufficient to calculate reliable stability constants of metal complexes with the use of both approaches. For 2, only approach neglecting the pK_(NH⁺) protonation constant was shown to be correct.The studied acids form dinuclear, [M₂L₃H_x], [M₂L₂H_x] and mononuclear MLH_x and ML₂H_x complexes with different degree of ligand protonation. Tendency to undergo some oligomerization with the increase in the metal and ligand concentration was demonstrated for the [CaLH] complex of 1 and 2. As far as 1 and 2 remain protonated, the Zn(II), Mg(II) and Ca(II) ions are coordinated exclusively through oxygen atoms of the phosphonate groups. The metal promoted proton dissociation from the NH⁺ ring atom takes place in alkaline pH.     

Modification effect of spherical zirconia with SiCl4 as a support of methylaluminoxane for heterogeneous single-site catalyst

Unmodified and SiCl₄-modified spherical zirconia-supported methylaluminoxane were used as cocatalyst for propylene polymerization as well as ethylene/1-hexene copolymerization in combined with Me₂Si(η³-C₁₃H₈)(η¹-N^tBu)TiMe₂ (1) at 0 °C. The modification with SiCl₄ improved the catalytic activity. The improvement was clearer in ethylene/1-hexene copolymerization than in propylene polymerization. The number average molecular weight (M_n) of polypropylenes increased linearly against the polymerization time regardless the cocatalyst used to give polymers with narrow molecular weight distribution (M_w/M_n < 1.32), indicating the living nature of the catalytic systems. Thus, propagation rate constant (k_p) and the number of active centers (C^*) were evaluated from M_n and the number of polymer-chains. When the zirconia was modified with SiCl₄, the k_p value decreased and the C^* increased. The latter effect was more significant to enhance the catalytic activity.     

Atom transfer radical polymerization of n-octyl acrylate under microwave irradiation

The atom transfer radical polymerization (ATRP) of n-octyl acrylate (OA) was successfully carried out using ethyl-2-bromobutyrate as an initiator, and CuBr/2,2^′-bipyridine (bpy) as a catalyst under microwave irradiation (MI) at 76.8 °C. The polymerization of n-octyl acrylate under MI showed linear first-order rate plots, a linear increase of the number-average molecular weight M_n with conversion, and low polydispersities, 1.1<M_w/M_n<1.4, where M_w is weight-average molecular weight. The ATRP of n-octyl acrylate is well controlled. Under the same experimental conditions, the apparent rate constant, k_p^app, under MI is larger apparently than that under conventional heating. In addition, the effects of concentration of catalyst and other factors on polymerization are reported.     

Neodymium alk(aryl)oxides-dialkylmagnesium systems for butadiene polymerization and copolymerization with styrene and glycidyl methacrylate

The application of well-defined neodymium alkoxides/aryloxides in combination with dialkylmagnesium reagents for 1,3-butadiene (BD) polymerization and copolymerization with styrene (St) and glycidyl methacrylate (GMA) has been investigated. The trinuclear complex Nd₃(Ot-Bu)₉(THF)₂ (1) provided a low-activity system for BD polymerization, even at high temperature, but with a high trans-1,4 stereospecificity (trans-1,4≈95%). Aryloxide complexes Nd(O-2,6-t-Bu₂-4-Me-Ph)₃(THF) (2) and Nd(O-2,6-t-Bu₂-4-Me-Ph)₃ (3) were found to give more active systems. The polymerization displayed a controlled character, i.e. a precise control of the molecular weight and a low polydispersity (M_w/M_n<1.30) for high catalyst concentration, keeping the same level of stereocontrol over the polymerization course. The statistical copolymerization of BD and styrene with those systems was successful. High-molecular weight copolymers (M_n up to 50?000 g mol⁻¹) with noticeable styrene content (3-15 mol%) were synthesized. Determination of the microstructure by ¹³C-NMR showed exclusively trans-1,4-BD-St sequences. The livingness of BD polymerization encouraged attempts of diblock copolymerization with GMA. In this case, low-molecular weight polymers with variable polydispersities were obtained (M_n<20?000 g mol⁻¹; M_w/M_n=1.4-5.0). The composition of the copolymers was analyzed by ¹H- and ¹³C-NMR and IR spectroscopies. SEC analyses confirmed the true nature of the diblock copolymer. The influence of the alkylating agent on those (co)-polymerizations was briefly studied. Finally, the mechanism of polymerization is also discussed.     

Bulk polymerization of rac-lactide initiated by guanidinate alkoxide complexes of rare earth metals. The molecular structure of the cluster [{(Me3Si)2NC(NPri)2}Nd]4(μ3-OPri)8Li7(μ2-Cl)3(μ3-Cl)2(μ4-Cl)2

The complexes {(Me₃Si)₂NC(NPrⁱ)₂}₂LnOBu^t (Ln = Y (1), Lu (2)) initiate the bulk polymerization of racemic lactide (LA) at 130 °C. At the monomer: initiator molar ratio ([LA]: 1) equal to 1000: 1, the quantitative conversion of the monomer is achieved within 6 h. The resulting polymers are characterized by a rather narrow monomodal molecular weight distribution (M _w/M _n = 1.46–1.82) and molecular weights up to 33400 g mol^?1. The molecular weights of the resulting polylactides measured by gel permeation chromatography are 3–11 times lower than the values calculated from the monomer: initiator ratio on the assumption of one growing polymer chain per catalytic center. The reaction of the in-situ prepared complex [(Me₃Si)₂NC(NPrⁱ)₂]NdCl₂ with 2 equiv. of PrⁱOLi produced the 11-nuclear cluster [{(Me₃Si)₂NC(NPrⁱ)₂}Nd]₄(μ³-OPrⁱ)₈Li₇(μ²-Cl)₃(μ³-Cl)₂(μ⁴-Cl)₂ (3), which was isolated in 62% yield. The structure of compound 3 was established by X-ray diffraction. Complex 3 initiates both the bulk and solution polymerization of rac-lactide. In the bulk polymerization at the molar ratio [LA]: [Nd] = 500: 1, the 89% conversion of the monomer was achieved within one hour. The polylactide thus synthesized has the molecular weight M _n = 19720 g mol^?1 and a rather narrow polydispersity M _w/M _n = 1.54.     

Quantitation of major elements with secondary ion mass spectrometry by using M 2 + -molecular ions

A new quantitation method, based on the detection of M ₂ ⁺ molecular ions, is presented. It has been shown that M ₂ ⁺ molecular ions are formed by a recombination process between independently sputtered M and M⁺ particles. Based on this formation mechanism, it will be demonstrated that M ₂ ⁺ molecular ions can be used to quantitate major elements. The method will be used for quantitation of an Al _x Ga_1?x As multilayer. Furthermore, it will be shown that some matrix effects can be explained by the energy dependence of instrument transmission.     

Fabrication of starch blend films with different matrices and their mechanical properties

The objective of the study was to determine the effects of molecular sizes of amylose (AM) and starch granules on the mechanical properties of thermoplastic starch (TPS) blend films. Leached amylose solution from cassava (CS_ AM) and mung bean (MB_AM), and two forms of amylopectin (AP) (granular; g and non-granular; ng) of waxy cassava (WxCS) starch were used. Four types of film matrices were fabricated and all TPS blend films contained same amount of AM and glycerol. Results displayed that molecular weight profiles of starch films and presence of granule remnants significantly controlled the film matrix formation, types of crystal formation, and percent of relative crystallinity (%RC) (p < 0.05). Tensile property of TPS films was controlled by %RC and presence of granule remnants. Percent elongation at break (%E_b) of TPS films increased when the films had a large range of molecular weight distribution (from 5.5 × 10⁷ g/mol to 0.4 × 10⁵ g/mol) and contained a high weight fraction (~58%) of starch molecules with M_w~0.4 × 10⁵ g/mol.     

Influences of molecular weight and crystalline structure on fracture behavior of controlled-rheology-polypropylene prepared by reactive extrusion

The molecular weight of ethylene-block-co-polypropylene (co-PP) was adjusted by reactive extrusion with the incorporation of dicumyl peroxide (DCP), and the effect of molecular weight on the crystallization behavior, crystal morphology, and fracture behavior was investigated. It was found that, with increasing DCP content, the molecular weight (MW) decreased and the polydispersity (M_w/M_n) slightly decreased. After modification, the number of spherulites with obscure boundaries increased, and the size of the spherulites was more even due to increasing amount of grafting and micro-cross-linking structures, generated in co-PP degradation, which were acting as nucleating agents. Evaluated by essential work of fracture method, the specific essential work of fracture, w_e, was found to be strongly dependent on the molecular weight, especially, on the number average molecular weight (M_n) linearly, while the specific non-essential work of fracture, βw_p, was enhanced with decreasing z-average molecular weight (M_z), probably owing to the reduction of ultra-high molecular weight component in degraded co-PP.     

Ultrasonic energy as a tool in the sample treatment for polymer characterization through matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Different ultrasonic devices including ultrasonic bath with dual frequency, sonoreactor and ultrasonic probe, were tested for their viability in the sample treatment for polymer characterization by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis. The effect of sonication frequency (35 kHz, 40 kHz and 130 kHz), sonication amplitude, and sonication time on the polymer's number-average molecular weight (M_n) and weight-average molecular weight (M_w) were investigated. The effect of those variables in the molecular mass distribution of three polymer standards, poly(styrene) 2000 Da and 10,000 Da and poly(ethylene glycol) 1000 Da, was evaluated. In addition, the influence of ultrasonic energy on the sample treatment as a function of the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI) matrix was also studied through two common standard matrices, dithranol and 2,5-dihydroxybenzoic acid. The results obtained show that the ultrasonic bath at 35 kHz is the best option for the purpose of fast sample treatment for polymer characterization. The M_n and M_w values obtained for this ultrasonic device and for the three polymers tested using dithranol as MALDI matrix, were not statistically different from the ones acquired with vortex mixing and also were in concordance with the values recommended by the polymer manufacturers.     

Synthesis and characterization of phosphorous-bridged bisphenoxy titanium complexes and their application to ethylene polymerization

Phosphorous-bridged bisphenoxy titanium complexes were synthesized and their ethylene polymerization behavior was investigated. Bis[3-tert-butyl-5-methyl-2-phenoxy](phenyl)phosphine tetrahydrofuran titanium dichloride (4a) was obtained by treatment of 3 equiv of n-BuLi with bis[3-tert-butyl-2-hydroxy-5-methylphenyl](phenyl)phosphine hydrochloride salt (3a) followed by TiCl₄(THF)₂ in THF. THF-free complexes 5a-5d were synthesized more conveniently by the direct reaction of MOM-protected ligands (2a-2d) with TiCl₄ in toluene. X-ray analysis of 4a revealed that the ligand is bonded to the octahedral titanium (IV) center in a facial fashion and two chlorine atoms possess cis-geometry. Complexes 4a and 5a-5d were utilized as catalyst precursors for ethylene polymerization. Complex 5c gave high molecular weight polyethylene (M_w = 1,170,000, M_w/M_n = 2.0) upon activation with Al(ⁱBu)₃/[Ph₃C][B(C₆F₅)₄] (TB). Ethylene polymerization activity of 5d activated with Al(ⁱBu)₃/TB reached 49.0 × 10⁶ g mol (cat) ⁻¹ h⁻¹.     

New Nb6Cl15 − xFx chlorofluoride: Stabilization of the Ta6Cl15 structure-type for binary Nb6 halide

The replacement of a small amount of chlorine by fluorine has made it possible to synthesize Nb₆Cl_{15 − x}F_xin chlorofluoride with the Ta₆Cl₁₅ structure-type. The crystal structures of two compositions in the solid solution (x = 2.2 (I) and x = 4.4 (II)) have been determined by single crystal X-ray diffraction and by isotypy with Ta₆Cl₁₅ (cubic, Ia-3d n° 230, a = 20.099(1) Å, V = 8119.2(1) ų, Z = 16, R = 0.047, R_w = 0.054 for (I) and a = 19.970(2) Å, V = 7964.3(8) ų, Z = 16, R = 0.067, R_w = 0.067 for (II). The structure is based on Nb₆L₁₂ⁱL_6/2^a-a (L = ligand) units in which F is randomly distributed on the inner positions for (I) and (II), and additionally on the apical-apical ones for (II). The unit-cell contains 16 units connected in the 3 directions by bent Nb-L^a-a-Nb bridges. This structure is different from the one encountered for Nb₆F₁₅ which exhibits 2 independent interpenetrating networks with linear Nb-F^a-a-Nb bridges. The interatomic distances obtained from structural data are discussed by comparison with the binary Ta₆Cl₁₅ and isotypic NaNb₆Cl₁₅ ternary chloride, taking into account electronic effects and the size of the fluorine. The small size of fluorine allows the reduction of the Nb-Nb intracluster distances by steric effects and thus the stabilization of the Ta₆Cl₁₅ structure-type with Nb₆ binary halides.     

Synthesis, crystal structure of bis(arylamido)lanthanide methyl complexes and their catalytic behavior for the polymerization of methyl methacrylate

Reactions of [N(C₆H₃i-Pr₂-2,6)(SiMe₃)]₂LnCl(THF) (Ln=Nd, Yb) with two equivalents of MeLi in a mixture solution of toluene and Et₂O gave [N(C₆H₃i-Pr₂-2,6)(SiMe₃)]₂LnCH₃(μ-CH₃)Li(THF)₃·PhCH₃ (Ln=Nd (1), Yb (2)) in good isolated yields as crystalline solids. The single-crystal structural analysis of 2 revealed that the coordination geometry of ytterbium ion is best described as a distorted pseudo-tetrahedron. Both 1 and 2 are active for the polymerization of methyl methacrylate to give syndiotactic-rich and high molecular weight polymers (M_n>10⁴) with relatively narrow molecular weight distributions (M_w/M_n<2).     

Living Carbocationic Copolymerizations. V. Synthesis of Isobutylene/p-Methylstyrene Copolymers with the Constant Copolymer Composition Technique in the Leidenfrost Reactor

Abstract

Living copolymerization of the isobutylene (IB)-p-methylstyrene (pMeSt) monomer pair in combination with the constant copolymer composition (CCC) technique produces high molecular weight ( M _n ≈ 100,000 g·mol^?1) and narrow molecular weight distribution ( M _w/ M _n ≈ 1.45) compositionally uniform IB/pMeSt copolymer molecules in the industrially important IB/pMeSt = 97–99/3–1 mol% composition range. Syntheses were carried out with TiCl₄ coinitiator in n-butyl chloride homogeneous solution at ?85°C by the use of the Leidenfrost reactor (i.e., by direct cooling of the charge with liquid nitrogen). In order to carry out the CCC technique it was necessary to obtain reliable copolymerization reactivity ratios. These investigations led to r_IB = 0.5 ± 0.1 and r _pMeSt = 10 ± 4. The attainment of CCC and living copolymerization conditions has been quantitatively demonstrated by dedicated diagnostic plots. Specifically, the attainment of CCC conditions was proven by the analysis of composite rate plots (comonomers input and corresponding copolymer formed versus time) and composition plots (comonomer composition in feed and copolymer formed versus weight of copolymer formed, W _p), and living copolymerization was proven by linearly ascending number-average molecular weight of copolymer ( M _n) versus W _p plots starting at the origin.     

Determination of the population,depopulation and the anisotropic spin lattice relaxation rates in the photoexcited triplet state of phenazine. A light modulation-EPR study

The photoexcited triplet state of phenazine in toluene glasses at 35 K is investigated by light modulation-EPR spectroscopy. From the transient EPR spectra and the kinetics in the three canonical orientations (p = x, y, z) the rate parameters are determined. Thus, the depopulation rate constants k_p, the anisotropic spin lattice relaxation rate constants W_p, and the ratios between the population constants A_p are calculated: k_x = (2.2 ± 0.3) × 10² s^?1, k_y = (0.21 ± 0.04) × 10² s^?1, k_z = (0.06 ± 0.03) × 10² s^?1, W_x = (8.6 ± 0.9) × 10³ s^?1, W_y = (11.0 ± 1.0) × 10³ s^?1, W_z = (14.0 ± 1.4) × 10³ s^?1, and A_x: _Ay:A_z ≈ 1:0.04:0.02. It is concluded therefore that the in-plane spin state |τ_x > is the active one.