Electron spin resonance study of polymerization of butadiene with tris(acetylacetonato)titanium and triethylaluminum

ESR spectra of homogeneous catalyst derived from tris(acetylacetonato)titanium(III) and triethylaluminum were observed at several temperatures from ?78°C, to +25°C, at molar ratios of aluminum to titanium of 1–108. At ?78°C, this catalyst yields a violet complex which shows an ESR signal with a g value of 1.959 and is associated with the first intermediate. At ?40°C to ?30°C, this signal decreases, and two signals with g values of 1.947 and 1.960 are observed. The latter two signals diminish at ?5°C to +10°C, while two kinds of new signals with g values of 1.965 and 1.969 appear overlapping each other. The structures of the species corresponding to these five signals are discussed on the basis of the ESR spectra, the intensity change, and the unpaired spin distribution. A new signal with a g value of 1.978 is found in the presence of butadiene at 25°C at Al/Ti > 8 and is assigned to a growing end of polybutadiene with this catalyst. The polymer yield increases remarkedly at Al/Ti molar ratios greater than 10. The microstructure of the resulting polymer consists almost completely of 1,2 units. The structure of the growing end is proposed to be a titanium (III) species containing two 1-substituted allyl groups, by comparison with the structure ascribed to the growing end of polybutadiene with n-butyl titanate-triethylaluminum catalyst.     

Electron spin resonance study on polymerization of alkyl acrylates with n-butyl titanate(IV)–triethylaluminum catalyst

n-Butyl titanate(IV)–triethylaluminum catalyst at Al/Ti molar ratios greater than 6 polymerizes methyl and n-butyl acrylates at ?78°C. The polymerization system which includes methyl acrylate at ?78°C, gives two ESR signals with g factors of 1.958 and 1.961 that overlap each other. The absorption intensity of the latter signal is approximately proportional to the polymer chain concentration calculated from polymer yield and the molecular weight. The polymerization system at Al/Ti ratios smaller than 3 has no catalytic activity on the polymerization and shows only the ESR signal with the g factor of 1.958. On the basis of these facts the ESR signal with the g factor of 1.961 is attributed to the active growing end of poly(methyl acrylate) with this catalyst. The character of this active growing end is discussed.     

Electron spin resonance study on polymerization of conjugated dienes by homogeneous catalyst derived from n-butyl titanate and triethylaluminum

Polymerizations of butadiene, penta-1,3-diene, and isoprene with n-butyl titanate–triethylaluminum catalyst are examined by ESR measurements on the polymerization state. At Al/Ti molar ratios greater than 2.9 where the conjugated dienes are polymerized, the polymerization system of butadiene always gives an ESR signal with a g value of 1.983 and with a hyperfine structure of about 19 components. This signal does not appear at all, even in the presence of the monomer, at Al/Ti molar ratios smaller than two where butadiene is not polymerized. The absorption intensity of the signal coincides fairly well with the concentration of polymer chain calculated from polymer yield and the molecular weight. On the basis of these facts, the signal is assigned to the growing end of polybutadiene with this catalyst. The structure of the growing end is proposed to have both two substituted π-allyl groups and an alkoxy group in coordination to titanium (III), by analysis of the hyperfine structure. The polymerization system of penta-1,3-diene and that of isoprene respectively, give a new signal with a g value of 1.983, although the signal for the former monomer has a hyperfine structure of 11 components and that for the latter monomer has no hyperfine structure. A structure for the growing end in the polymerization of each of these two monomers analogous to that of the growing end of polybutadiene is proposed.     

Monomer-isomerization polymerization. XIII. Monomer-isomerization polymerization of 1,4-cyclohexadiene with Ziegler-Natta catalyst

1,4-Cyclohexadiene underwent monomer-isomerization polymerization to yield poly(1,3-cyclohexadiene) with a Ziegler-Natta catalyst comprising TiCl₄–Al(C₂H₅)₃ catalyst with Al/Ti molar ratios of 0.5–3.0 at 60°C for 96 hr. Good yields of polymer were obtained (49.5% yield at Al/Ti = 3.0; [η] = 0.04 dl/g). The infrared and NMR spectra of the polymer were identical to those of poly-(1,3-cyclohexadiene), confirming that 1,4-cyclohexadiene first isomerizes to 1,3-cyclohexadiene and then homopolymerizes to give poly-1,3-cyclohexadiene. 1,3-Cyclohexadiene polymerized without isomerization easily in the presence of TiCl₃–Al(C₂H₅)₃ catalyst at Al/Ti molar ratios of 0.5–3.0 at 60°C for 3 hr (76.3% yield at Al/Ti = 3.0; [η] = 0.06 dl/g).     

Cyclopolymerization. VI. Polymerization mechanism of N-methyl-N-allylmethacrylamide at lower temperature

Mechanistic investigations on the polymerization of N-methyl-N-allylmethacrylamide (MAMA) at lower temperature were carried out based upon the ESR studies of MAMA and its monofunctional counterparts irradiated with ⁶⁰Co γ rays. Cyclopolymerizability of MAMA was also studied in connection with the hindered rotation about its amide C? N bond. The propagating radical observed is only related to the methacryl group but not to the allyl group both in MAMA and its monofunctional counterparts. Polymerization at ?78°C yielded a polymer with a lower degree of cyclization(88.8%) as compared with that of polymers formed at higher temperatures (93.5% above 0°C). A structural study revealed that the increment of the unsaturation in the poly-MAMA obtained at ?78°C is due to the allyl group and the content of pendant methacryl group is almost unchanged over the temperature range from ?78 to 120°C. These results led to the conclusion that the polymerization of MAMA at ?78°C proceeds mainly through the methacryl group, the rate-determining step is the cyclization reaction, and, in addition, cyclization reaction scarcely occurs when it polymerizes through the allyl group. Since MAMA is frozen into a glassy state, the effect of glass transition temperature (T_g) has been studied and it was suggested that the polymerization of MAMA proceeds only above T_g.     

CO<Subscript>2</Subscript> capture by Mg–Al and Zn–Al hydrotalcite-like compounds

Hydrotalcite-like compounds (HTC) are distinguished by their properties for CO₂ capture, like high surface area, basic sites, thermal stability and good adsorption/desorption efficiency. Mg–Al e Zn–Al HTCs with Al³⁺ molar ratios x = 0.20, 0.28 and 0.33 were synthesized by coprecipitation, and subsequently calcined at 400 °C. For both HTCs, X-ray diffraction patterns have attested the formation of mixed oxides through calcination. The amount of basic sites, measured by temperature-programmed desorption of CO₂, decreases as x increases. The CO₂ adsorption was performed in a thermogravimetric balance using an adsorption temperature of 50 °C. Mg–Al and Zn–Al samples with x = 0.33 molar composition presented the highest CO₂ adsorption, 0.91 and 0.21 mmol g^?1, respectively. The Langmuir isotherm fitted well to the experimental data. It was also found that increasing the number of adsorption/desorption cycles the CO₂ adsorption decreases, which is associated with the irreversible chemisorption.     

Determination of the cubic to hexagonal structure transition in the metastable system TiN-AlN

Structural transitions of metastable Ti_1–xAl_xN coatings on technically relevant substrates were determined as a function of the Ti/Al ratio. Ti_1–xAl_xN films with different Ti/Al ratios were deposited on high speed steel (HSS) substrates at substrate temperatures of 300?° and 500?°C by means of reactive magnetron sputtering ion plating (MSIP). A Ti/Al compound target was used as well as a cluster arrangement of one Ti and one Al target for comparison. The composition of the films was determined by electron probe microanalysis (EPMA), the crystallographic structure by thin film X-ray diffraction (XRD). The analyses revealed that films deposited with Ti/Al ratios of 44/56 and 36/64 had grown in cubic NaCl structure, a film with a Ti/Al ratio of 32/68 was two-phase, and a Ti/Al ratio of 25/75 led to a hexagonal film in wurtzite structure. Only small differences of the lattice parameters could be observed in dependence of temperature: At 300?°C the lattice parameters of the cubic structure corresponded exactly to Vegard‘s law, whereas they slightly decreased in the films deposited at 500?°C. The application of a cluster arrangement instead of a compound target resulted in nearly the same lattice parameters and peak shapes.     

Cubic Mesoporous Titanium Phosphonates with Multifunctionality

Cubic mesoporous titanium phosphonate materials with bridged organic groups inside the framework were synthesized by means of a one‐pot hydrothermal autoclaving process, with the assistance of cationic surfactant cetyltrimethylammonium bromide. 1‐Hydroxyethylidene‐1,1‐diphosphonic acid was used as the coupling molecule. A typical cubic mesophase with surface area of 1052 m² g^?1 and pore size of 2.6 nm was confirmed by XRD, TEM, and N₂ sorption analysis. The organophosphonate groups were homogeneously incorporated in the network of the mesoporous solids, as revealed by FTIR and magic‐angle spinning (MAS) NMR spectroscopy, and thermogravimetry and differential scanning calorimetry (TG‐DSC) measurements. The synthesized hydroxyethylidene‐bridged cubic mesoporous titanium phosphonates proved to be thermally stable up to 350 °C, with a well‐preserved hybrid framework and cubic mesoporous architecture. The obtained cubic mesophase could be transformed into a hexagonal mesophase by simply adjusting the molar ratios of the added raw materials, namely, a Ti/P molar ratio of 1:4 and a CTAB/Ti molar ratio of 1.9–2.3 for the cubic phase and Ti/P molar ratio of 3:4 and CTAB/Ti molar ratio of 0.1–0.4 for the hexagonal phase. The cubic hybrid materials could be used as efficient photocatalysts for the photodegradation of rhodamine B. Moreover, they were also used for adsorption of CO₂ and heavy metal ions and exhibited a significant capture amount of around 1.0 mmol g^?1 for CO₂ molecules at 35 °C and high adsorption capacity of 28.5 μmol g^?1 for Cu²⁺ ions with good reusability, which demonstrated their promising potential in environmental remediation.     

Influence of Isosorbide on Glass‐Transition Temperature and Crystallinity of Poly(butylene terephthalate)

Copolyesters of isosorbide and 1,4‐butane diol were prepared by Ti(OBu)₄‐catalyzed transesterifications with dimethyl terephthalate in bulk at temperatures up to 250°C. The content of isosorbide was considerably lower than expected from the feed ratio and the molar masses were low, so that no DSC measurements were conducted. Copolycondensations of isosorbide and 1,4‐butane diol with terephthaloyl chloride were either performed in dichloromethane at 40°C or in toluene at 100°C. The second method gave the higher molar masses. However, both series of polycondensations had the content of isosorbide roughly paralleled the feed ratios in common. The DSC measurements revealed that even 6 mol% of isosorbide is sufficient to raise the glass‐transition temperature (T_g) by 10–12°C (up to 55°C). With 50 mol% of isosorbide, the T_g reaches 100°C. Yet, incorporation of isosorbide also reduces the melting temperature T_m and the degree of crystallinity, and a mol percentage above 30% prevents crystallization completely. In summary, incorporation of isosorbide allows for fine‐tuning of T_g and T_m of poly(butylene terephthalate) over a wide range.     

Study of the reaction of MoOS2(S2CNR2)2 with PPh3 in 1,2-dichloroethane: Part II. Detection of reaction intermediate pentavalent molybdenum using ESR method at low temperature

Intermediate product of the reaction of MoOS₂(S₂CNR₂)₂ and PPh₃ in dichloroethane has been detected by ESR spectroscopy. Two ESR signals have been observed at low temperature in the reaction system which was stopped by quenching it in liquid nitrogen. The g values are 2.020 ± 0.001 and 1.972 ± 0.001 respectively. The signal at g = 2.020 is attributed to a reaction intermediate with pentavalent molybdenum. A reaction mechanism has been proposed which is consistent with the observation of pentavalent molybdenum as the intermediate in the process of reaction.     

Change with temperature of the ESR spectra of peroxy radicals trapped in irradiated polytetrafluoroethylene

The ESR spectra of peroxy radicals in irradiated powders and oriented samples of polytetrafluoroethylene (PTEE) have been measured with a K-band spectrometer, and the principal values and directions of the g tensor were determined both at room temperature and at 77°K. In contrast to the spectra of the usual peroxy radicals, those trapped in γ-irradiated PTFE exhibited an ESR spectrum apparently having a larger principal value for g⊥ than for g∥ when measured at room temperature, although the normal principal values were observed at 77°K. As for the directions of the principal axes, g∥ was directed along the chain axis at room temperature and was perpendicular to the chain axis at 77°K. From the temperature change of the g tensor and the line shapes in the oriented samples, it is shown that the observed temperature change of the spectra is due to rapid rotation at room temperature around the chain axis rather than around the C? O bond axis. Assuming this, the apparent principal values of the g tensor at room temperature were calculated from the g tensor obtained at 77°K. for the rigid state, and the results are in good agreement with observations at room temperature. A structure for the peroxy radicals is also proposed. In addition, the spectral line shape function for the uniaxially oriented samples has been derived.     

Characterisation of Siliceous Extra‐Framework Species in DAY Zeolites by 29Si MAS NMR and IR Spectroscopic Measurements

Dealuminated Y zeolites (DAY) were obtained by steaming of NH₄NaY at temperatures between 450 °C and 700 °C. They were characterised by means of ²⁷Al and ²⁹Si MAS NMR, IR spectroscopic and XRD measurements. The Si/Al framework ratios of samples were calculated using the ²⁹Si MAS NMR signal intensities, the wave numbers of the double‐ring vibration band w_DR and the asymmetrical TOT valence vibration w_TOT of IR spectra as well as the XRD lattice constant a₀. In contrast to actual Si/Al ratio obtained from w_DR and a₀, the NMR spectroscopic and w_TOT values were determined to be too high because of the superposition of the signals coming from dealuminated zeolite framework and silica gel which forms in the zeolite as a result of steaming. The differently determined Si/Al ratios characterise the siliceous extra‐framework species.     

Effects of POSS nanoparticles on glass transition temperatures of ultrathin poly(t‐butyl acrylate) films and bulk blends

As a model system, thin films of trisilanolphenyl‐POSS (TPP) and two different number average molar mass (5 and 23 kg mol^?1) poly(t‐butyl acrylate) (PtBA) were prepared as blends by Langmuir–Blodgett film deposition. Films were characterized by ellipsometry. For comparison, bulk blends are prepared by solution casting and the samples are characterized via differential scanning calorimetry. The increase in T_g as a function of TPP content for bulk high and low molar mass samples are in the order of ～10 °C. Whereas bulk T_g shows comparable increases for both molar masses (～10 °C), the increase in surface T_g for higher molar mass PtBA is greater than for low molar mass (～22 °C vs. ～10 °C). Nonetheless, the total enhancement of T_g is complete by the time 20 wt % TPP is added without further benefit at higher nanofiller loads. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 175–182     

Thermal cis–trans isomerization and decomposition of polyacetylene

Thermal cis-trans isomerization and decomposition of polyacetylene film prepared with a Ti(OC₄H₉)₄–Al(C₂H₅)₃ (Al/Ti = 4) system were investigated under inert gas or in vacuum by means of thermal analysis and infrared spectroscopy. Thermograms of differential thermal analysis of cis-polyacetylene revealed the existence of two exothermic peaks at 145 and 325°C and one endothermic peak at 420°C which were assigned to cis-trans isomerization, hydrogen migration accompanied with crosslinking reaction, and thermal decomposition, respectively. The isomerization was followed by infrared spectroscopy over the temperature range 75–115°C. The reaction did not obey simple kinetics. The apparent activation energy for the cis-trans isomerization was 17.0 kcal/mole for the polymer containing 88% cis configuration and increased with increasing trans content up to 38.8 kcal/mole for 80% trans content.     

Simultaneous polymerization and formation of polyacetylene film on the surface of concentrated soluble Ziegler-type catalyst solution

A direct method of simultaneously polymerizing and forming acetylene monomer to produce uniformly thin films of polyacetylene was investigated in terms of catalyst system, catalyst concentration, and polymerization temperature. The best catalyst was a Ti(OC₄H₉)₄–Al(C₂H₅)₃ system (Al/Ti = 3–4) and the critical concentration was 3 mmole/l. of Ti(OC₄H₉)₄. Below the critical concentration, only a solid or a powder was obtained. The configuration of the polymers obtained depends strongly upon the polymerization temperature. Thus an all-cis polymer was obtained at temperatures lower than ?78°C, whereas an all-trans polymer resulted at temperatures higher than 150°C. Observations either in an electron microscope by direct transmission or in a scanning electron microscope showed that the film is composed of an accumulation of fibrils about 200–300 Å in width and of indefinite length.     

Electron spin resonance study of poly-3,3-bis(chloromethyl) oxetane irradiated with electron beams and ultraviolet light

Poly-3,3-bis(chloromethyl)oxetane (poly-BCMO) was irradiated at ?196°C with electron beams and ultraviolet light, and observed ESR spectra were compared. A three-line spectrum (coupling constant of about 21 gauss) and a two-line spectrum (coupling constant of about 18 gauss) were observed after irradiation with electron beams in vacuo. They were attributed to free radicals and respectively. On the other hand, a three-line spectrum (coupling constant of about 20 gauss) and an asymmetric singlet spectrum were observed after ultraviolet irradiation in vacuum. They were assigned to free radicals and ? CH₂? O·, respectively. Mechanisms of radical formation were discussed in each case. When poly-BCMO was irradiated with electron beams at ?196°C in the presence of air, peroxy radicals were produced after subsequent treatment at ?78°C. The reaction between alkyl radicals and oxygen molecules was found to be diffusion-controlled.     

The use of ESR technique for assessment of heating temperatures of archaeological lentil samples

Heat-induced paramagnetic centers in modern and archaeological lentils (Lens culinaris, Medik.) were studied by X-band (9.3 GHz) electron spin resonance (ESR) technique. The modern red lentil samples were heated in an electrical furnace at increasing temperatures in the range 70–500 °C. The ESR spectral parameters (the intensity, g-value and peak-to-peak line width) of the heat-induced organic radicals were investigated for modern red lentil (Lens culinaris, Medik.) samples. The obtained ESR spectra indicate that the relative number of heat-induced paramagnetic species and peak-to-peak line widths depends on the temperature and heating time of the modern lentil. The g-values also depend on the heating temperature but not heating time. Heated modern red lentils produced a range of organic radicals with g-values from g = 2.0062 to 2.0035. ESR signals of carbonised archaeological lentil samples from two archaeological deposits of the Van province in Turkey were studied and g-values, peak-to-peak line widths, intensities and elemental compositions were compared with those obtained for modern samples in order to assess at which temperature these archaeological lentils were heated in prehistoric sites. The maximum temperatures of the previous heating of carbonised UA5 and Y11 lentil seeds are as follows about 500 °C and above 500 °C, respectively.     

Preparation of acid–base bi-functional hydrotalcite based catalyst for converting Vietnamese coconut oil to green hydrocarbons

Acid–base bi-functional hydrotalcite like compounds based on partial incorporation of Al³⁺ into brucite structure of Mg(OH)₂ with various molar ratios were prepared through co-precipitation method. The co-precipitation of the precursors produced precipitations followed by drying at 120 °C for 12 h and calcination in air flow at 500 °C for 6 h to obtain the catalysts (Mg–Al HLCs). Many techniques including XRD, TG–DTA, EDX, NH₃-TPD, CO₂-TPD, GC–MS and XANES were used to characterize and optimize Mg/Al molar ratio based on the thermal stability of the Mg–Al HLCs and their activities in decarboxylation process of coconut oil. The results showed that the best molar ratio of Mg/Al was 3/1 providing a stable hydrotalcite like structure, and the catalyst possessed both acid and base sites on its surface enhancing its activity and selectivity in the decarboxylation process. The catalysts revealed high performance in the decarboxylation process of coconut oil established at 400 °C for 4 h for green hydrocarbons belonging to kerosene fractions.     

Enhancement of stereospecificity in isoprene polymerization with alkylaluminum–titanium chloride catalysts through use of carbon disulfide

The effect of CS₂ on isoprene polymerization with triisobutylaluminum-titanium tetrachloride catalysts was studied at Al/Ti ratios of optimum (0.9) and higher values. In the absence of CS₂, appreciable amounts of low molecular weight oils (“extractables”) were formed at the expense of cis-1,4-polyisoprene with higher than optimum Al/Ti ratios. Small amounts of CS₂ were found to prevent extractables formation and allow attainment of higher yields of cis-1,4-polyisoprene. The optimum CS₂/Ti chloride molar ratio (0.1) was independent of the Al/Ti ratio of the catalyst. Polymer microstructure and dilute solution viscosity were unaffected by CS₂. The results support the theory that the catalyst surfaces hold two types of active sites: p-sites, which initiate polymerization, and o-sites, which lead to oligomerization. CS₂ appears to enhance polymerization by coordinating selectively at the o-sites. The predominance of oligomerization at the higher Al/Ti ratios was attributed to a destruction of p-sites by excess trialkyl-aluminum.     

Electrochemical and Structural Characterisation of Dip-Coated Fe/Ti Oxide Films Prepared by the Sol-Gel Route

Thin solid films of mixed Fe/Ti oxide composition (Fe/Ti molar ratios: 0.5∶1, 1∶1, 1.5∶1) have been made from Fe(NO₃)₃ alcoholic solution to which Ti(OiPr)₄ was added. Films have been deposited by the dip-coating technique and heat-treated at 300°C and 500°C. Powders of Fe/Ti oxide heat-treated at 300°C are amorphous, while powders annealed at 500°C for 40 hours transformed to mixed rutile, pseudobrookite and hematite phases. The structure of the XRD amorphous films was identified with the help of near-normal reflection absorption (6°) (IRRA) and near-grazing incidence angle (NGIA) spectroscopy. NGIA FT-IR spectra of films are characterised with a single phonon mode appearing in the spectral range 600–950 cm⁻¹ which shifts with increasing Ti concentration from 675 cm⁻¹ (Fe₂O₃) to 904 cm⁻¹ (TiO₂) thus exhibiting one-mode behavior. Electrochemical investigations made with the help of cyclic voltammetry (CV) and chronocoulometry (CPC) performed in 0.01M LiOH and in 1M LiClO₄/propylene carbonate electrolytes revealed that films are able to uptake reversibly Li⁺ ions with a charge capacity (Q) per film thickness (d) in the range 0.1–0.26 mC/cm²nm and 0.06 mC/cm²nm, respectively. The temperature at which the films were prepared alters the rate of Li⁺ insertion which is faster for less compact films obtained at 300°C. In situ UV-VIS spectroelectrochemical measurements revealed that Fe/Ti oxide films bleached in the UV spectral region (300 nm<λ<450 nm) and colored in the VIS spectral region (450 nm<λ<800 nm), thus exhibiting mixed anodic and cathodic electrochromism.