Poly(ethyl-n-butylsilylene): Structural,thermal, and flow properties of a liquid crystalline polysilane

Poly(ethyl-n-butylsilylene) (PEBS) was synthesized by sodium coupling of ethyl-n-butyldichorosilane and separated into fractions with differing molecular weights,M _w=1.4×10⁶ and 2.0×10⁴. Both fractions were studied by differential scanning calorimetry and by X-ray diffraction, UV spectroscopy, polarizing optical microscopy, and capillary rheometry, all as a function of temperature. Both samples adopt a hexagonal columnar liquid crystalline structure at room temperature and below. They undergo a weak endothermic transition at ?20°C and a first-order phase transition to a nematic liquid crystalline form at 90°C for the low and 170°C for the highM _w fraction. Melting to an isotropic liquid takes place at 106°C for the low and 185°C for the highM _w polymer. Both samples undergo two successive thermochromic transitions in the UV, one near the first-order exothermic transition and one near the ?20°C transition; the reasons underlying these thermochromic transitions are discussed. Flow properties of PEBS were investigated as a function of molecular weight.     

Some recent developments in polysilane chemistry

(I) Ordered and disordered polysilane copolymers: Condensation of ClSiMe₂Si(n-Hex)₂SiMe₂Cl with Na/K in toluene at 90°C produced a polymer with a strongly bimodal molecular weight distribution. The high-M _w and low-M _w portions were separated by fractional precipitation with 2-propanol, and the properties of the two fractions were investigated.²⁹Si-NMR spectra show that the low-M _w fraction is fully ordered but the high-M _w fraction is randomized. (II) Liquid crystalline polysilanes: Condensation ofn-Bu(n-Hex)SiCl₂ with Na in toluene led to a homopolymer which is a rubbery solid at 25°C. The polymer undergoes a second-order transition at –45°C and a first-order (melt) transition at –20°C. X-ray diffraction shows that the polymer has the same structure, a columnar hexagonal lattice, in all three phases; from –20 to >200°C, it exists in a columnar liquid crystalline mesophase. Similar hexagonal mesophases were observed at 25°C for the family of copolymers, (n-Hex₂Si) _n (Alk₂Si) _m , Alk =n-Pentyl,n-Bu,n-Pr, Et, Me.     

Spontaneous Ring-Opening Copolymerization of 1,1,2,2-Tetramethyl-1,2-Disilacyclobutane with Styrene

l,l,2,2-Tetramethyl-l,2-disilacyclobutane (TMDSCB), obtained by alkali metal vapor dehalogenation of l,2-bis(chlorodimethylsilyl(ethane, undergoes room-temperature spontaneous ring-opening Copolymerization with styrene (St) and results in a rubbery copolymer (M _w = 1.6 × 10⁵, M _w/M _n = 4.4). In contrast to a thermoplastic homopolymer of TMDSCB (m.p. 110°C) that is obtained by the same procedure in the absence of styrene, the copolymer exhibits two-phase behavior (Tg = – 37°C, m.p. 106°C), with the heat of melting being considerably lower in the case of the copolymer (cf. 49.0 and 4.8 J g^–1). Spectral and analytical data are consistent with a copolymer structure, [(Me₂SiCH₂CH₂SiMe₂) _k (CH₂CHPh)_l] _n , where k = 3, l = 1 (36%), and k = 6, l = 2 (64%).     

Bimetallic nickel complexes of trimethyl phenyl linked salicylaldimine ligands: Synthesis, structure and their ethylene polymerization behaviors

Bimetallic salicylaldimine-nickel complexes, 2,4,6-Me₃-1,3-{[NCH–(3′-R-5′-Y-2′-O–C₆H₃)-κ²-N,O]Ni(Ph) (PPh₃)}₂ [R = tert-Bu, Y = Me, 1b; R = Ph, Y = H, 2b] were prepared and their catalytic behaviors of ethylene polymerization were investigated. The bimetallic complex 2b shows higher activities (2.9 × 10⁵ g PE mol⁻¹ Ni h⁻¹) for ethylene polymerization and affords polymer with high molecular weight (M_w = 1.41 × 10⁵) and broad molecular weight distribution (M_w/M_n = 6.1) than its mononuclear matrix, {[(2,6-Me₂C₆H₃)–NCH–(3′-Ph-2′-O–C₆H₃)-κ²-N,O]Ni(Ph)(PPh₃)} (3) (Activity = 5.5 × 10⁴ g PE mol⁻¹ Ni h⁻¹; M_w = 1.86 × 10⁴; M_w/M_n = 2.8).     

1,4-pentadien-3-one-1-p-hydroxyphenyl-5-p-phenyl Acrylate: Crosslinking Studies and Reactivity Ratios with Glycidyl Methacrylate

1,4-pentadien-3-one-1,5-bis(p-hydroxyphenyl) (PBHP) was synthesized by reacting p-hydroxybenzaldehyde and acetone in the presence of HCl gas. 1,4-pentadien-3-one-1-p-hydroxyphenyl-5-p-phenyl acrylate (HPA) was prepared by reacting PBHP with acryloyl chloride in ethyl methyl ketone (EMK) medium at 0°C. Copolymerization of different feed compositions of HPA with glycidyl methacrylate (GMA) was carried out using benzoyl peroxide (BPO) as initiator in EMK solvent under nitrogen atmosphere at 70±1°C. Polymers thus synthesized were characterized by IR and NMR (¹H/¹³C) spectroscopic techniques. Reactivity ratios of the monomers were calculated from the ¹H NMR data by applying linearization methods such as Fineman–Ross, Kelen–Tudos and extended Kelen–Tudos methods. Photocrosslinking property of the polymer samples was studied using the solvent method. Thermal stability of the polymers were measured using thermogravimetric analysis. Molecular weights (M _w and M _n) and polydispersity value of the polymer were determined using gel permeation chromatographic technique.     

Synthesis, Characterization and Anti-microbial Activity of Oligo-N-2-aminopyridinylsalicylaldimine and Some Oligomer-metal Complexes

The oxidative polycondensation and optimum reaction conditions of N-2-aminopyridinylsalicylaldimine using air oxygen, H₂O₂ and NaOCl were determined in an aqueous alkaline solution between 40–90°C. Oligo-N-2-aminopyridinylsalicylaldimine (OAPSA) was characterized by using ¹H-NMR, FT-IR, UV-vis and elemental analysis. N-2-aminopyridinylsalicylaldimine was converted to oligomer by oxidizing in an aqueous alkaline medium. The number average molecular weight (M _n), weight average molecular weight (M _w) and polydispersity index (PDI) values were found to be 7487 gmol^–1, 7901 gmol^–1 and 1.06, respectively. According to these values, 70% of N-2-aminopyridinylsalicylaldimine turned into oligo-N-2-aminopyridinylsalicylaldimine. During the polycondensation reaction, a part of the azomethine (–CH=N–) groups oxidized to carboxylic (–COOH) group. Besides, the structure and properties of oligomer-metal complexes of oligo-N-2-aminopyridinyl salicylaldimine (OAPSA) with Cu (II), Ni (II), and Co (II) were studied by FT-IR, UV-vis DTA, TG and elemental analysis. Anti-microbial activities of the oligomer and its oligomer-metal complexes have been tested against C. albicans, L. monocytogenes, B. megaterium, E. coli, M. smegmatis, E. aeroginesa, P. fluorescen and B. jeoreseens. Also, according to the TG and DTA analyses, oligo-N-2-aminopyridinylsalicylaldimine and its oligomer-metal complexes were found to be stable thermo-oxidative decomposition. The weight loss of OAPSA found to be 20%, 50% and 98% at 350°C, 535°C and 1000°C, respectively.     

Synthesis of Poly(cyclohexyl vinyl ether-<Emphasis Type="Italic">b</Emphasis>-isobutylene-<Emphasis Type="Italic">b</Emphasis>-cyclohexyl vinyl ether) Triblock Copolymer by Living Cationic Sequential Copolymerization

Summary The living cationic polymerization of cyclohexyl vinyl ether (CHVE) and sequential block copolymerization of isobutylene with CHVE were carried out by the so-called capping-tuning technique in hexanes/CH₃Cl solvent mixtures at –80 °C. It involves capping the initiator, 2-chloro-2,4,4-trimethylpentane (TMPCl), or the living polyisobutylene (PIB) chain end with 1,1-ditolylethylene in the presence of titanium(IV) (TiCl₄), followed by fine-tuning of the Lewis acidity with the addition of titanium(IV) isopropoxide (Ti(OIp)₄) to match the reactivity of CHVE. Well-defined PCHVE, PIB-b-PCHVE and PCHVE-b-PIB-b-PCHVE with predesigned molecular weights and narrow molecular weight distributions (M_w/M_n<1.1) were thus prepared with [Ti(OIp)₄]/[TiCl₄] ratios of 1.6–1.8. Differential scanning calorimetry of the triblock copolymers showed two T_gs (–62 °C for PIB and 61 °C for PCHVE) suggesting a microphas-separated morphology of the triblock copolymers and the potential use of them as thermoplastic elastomers.     

Potentiometric measurements of ionic transport parameters in poly(ethylene oxide)-LiX electrolytes

An electrochemical technique based on concentration cell e.m.f. measurements is used to determine the lithium transference number and diffusion coefficient in poly(ethylene oxide)-lithium salt complexes. Measurements were carried out at 90°C on PEO–LiI, PEO–LiClO₄ and PEO–LiCF₃SO₃ electrolytes. According to the phase diagram of the PEO-lithium salt system these complexes are fully amorphous at 90°C. Accurate determination oft _Li ⁺ by the e.m.f. concentration cell method generally requires knowledge of the mean salt activity coefficients. However, this becomes unnecessary when the two electrolyte concentrations differ only slightly. As a first step the mean salt activity coefficient was estimated using a galvanic cell of the lithium/PEO-LiX/MX _n /M type withM ⁿ⁺=Ag⁺ or Pb²⁺, and X^–=I^– or CF₃SO₃ ^–. The resulting lithium transference numbers are 0.34 for the PEO–LiI complex and 0.7 for PEO–LiCF₃SO₃. Discrepancies between thet _Li ⁺ values can be explained by the formation of triplets in the PEO–LiCF₃SO₃ electrolyte. By recording concentration cell potential versus time and comparing with theoretical curves, the salt lithium diffusion coefficient was obtained.D _LiI was found to be around 4×10^–8 cm² s^–1 in PEO–LiI and 8×10^–8 cm² s^–1 in PEO–LiCF₃SO₃ at 90°C. These results suggest a liquid-like behaviour for the microscopic transport mechanism.     

Preparation and properties of raney nickel electrodes on Ni-Zn base for H2 and O2 evolution from alkaline solutions Part I: electrodeposition of Ni-Zn alloys from chloride solutions

Experimental results for the electrodeposition of Ni-Zn alloys from chloride solutions, with addition of H₃BO₃ and without other additives, in a laboratory cell with a perforated nickel sheet cathode and with recirculating electrolyte are presented. The dependence of the zinc content in the alloy on the following operating conditions was investigated: cathodic current density, 1.0–20.0 A dm^–2; temperature, 35–65°C; pH 1.5–5.5; total molarity,M _tot=M _Ni ²⁺ +M _Zn ²⁺ =1.1–2.8 M; and, molar ratio,P=M _Ni ²⁺ /M _Zn ²⁺ =1.0–15. Depending on the operating conditions the Zn content in the alloy varied over the range 22–88 mol%. In separate experiments galvanostatic polarization curves were measured in the direction of increasing and then decreasing cathodic current density in the range 0.1–20.0 A dm^–2 with all other operating conditions as used for electroplating experiments. In all cases significant hysteresis effects were observed. It was found that the current efficiency for the electrodeposition of Ni-Zn alloys from chloride solutions as a function of the zinc content in the alloy showed a sharp minimum of about 55% atX _Zn=55 mol % irrespective of other operating conditions.     

Living cationic polymerization of isobutyl vinyl ether initiated by the trimethylsilyl iodide/zinc iodide system

Summary Trimethylsilyl iodide in conjunction with zinc iodide (Me₃SiI/ZnI₂) as an initiating system led to living cationic polymerization of isobutyl vinyl ether in toluene at 0 or –40°C or in methylene chloride at –40°C (ZnI₂ was dissolved in acetone). The number-average molecular weight of the polymers was directly proportional to monomer conversion and in excellent agreement with the calculated value assuming that one polymer chain forms per unit trimethylsilyl iodide. At room temperature (+25°C), however, the polymerization failed to give perfectly living polymers; the polymer molecular weight was smaller than the calculated value. On addition of a fresh feed of monomer at the end of the polymerization at –40°C, the added feed was smoothly polymerized at nearly the same rate as in the first stage, and the polymer molecular weight continued to increase in direct proportion to monomer conversion. Throughout the reaction, the molecular weight distribution of the polymers stayed very narrow (M_w/M_n< 1.1).Living cationic polymerization of vinyl ethers by electrophile/Lewis acid initiating systems, part 2. For part 1 see ref. 2     

Living cationic polymerization of p-methoxystyrene by hydrogen iodide/zinc iodide at room temperature

Summary Cationic polymerization of p-methoxystyrene initiated by HI/ZnI₂ in toluene afforded living polymers not only at low temperature (–15°C) but at room temperature (+25°C) as well. The number-average molecular weight of the polymers was directly proportional to monomer conversion and in excellent agreement with the calculated value assuming that one polymer chain forms per unit hydrogen iodide. On addition of a fresh feed of monomer at the end of the first-stage polymerization, the added feed was smoothly polymerized at nearly the same rate as in the first stage; the polymer molecular weight further increased in direct proportion to monomer conversion and was close to the calculated value for living polymer. Throughout these reactions, the molecular weight distribution of the polymers stayed very narrow (¯M_w/¯M_n<1.1). This is the first example of living cationic polymerizations of styrene derivatives that proceed even at room temperature.     

High-molecular weight diepoxide-dicarboxylic acid addition polymers

Summary The addition polymerization of 2,2-bis[4-(2,3-epoxypropoxy)phenyl] propane (DGEBA) and dicarboxylic acid results in high molecular weight addition polymers (M_n 8000–13000). Their molecular weight distribution is rather broad (M_w/M_n=11,6) due to side reactions such as transesterification and formation of ether linkages. Due to the incorporation of the aliphatic dicarboxylic acid moieties in the polymer backbone, the addition polymers show relatively low glass transition temperatures ranging from 26 to 45 °C.     

Synthesis of a cis-rich,living poly[(o-methylphenyl)acetylene] by use of the MoOCl4-n-Bu4Sn-EtOH catalyst

Summary Polymerization of (o-methylphenyl)acetylene (o-MePA) by MoOCl₄-n-Bu₄Sn-EtOH catalyst in toluene at 0°C provided a cis-rich living polymer; cis 77%, M _w/M _n=1.21. The polymerization at -30°C gave results similar to those for 0°C, whereas the polymer obtained at 30°C exhibited a broader molecular weight distribution (MWD) and a lower cis content. Among several organotin compounds, only n-Bu₄Sn was effective for the living polymerization of o-MePA. The bulkier the alkyl group of alcohols as the third catalyst component, the broader the MWD of the polymer, while the geometrical structure was not affected by the alcohols.     

Polymerization of Vinyl Acetate Initiated by a Copper Alginate Coordination Polymer Film/Na2SO3/H2O System

A hydrophobic film of copper alginate coordination polymer was prepared by soaking a sodium alginate film in a 13% CuCl₂ aqueous solution at room temperature for more than 24 h. The composition, structure, and property of copper alginate as a coordination catalyst were studied by ESR, IR, XPS, and electric conductivity methods. It was shown that a low-spin copper complex was formed as a result of the acceptance by dsp² hybrid orbitals of nonpaired electrons transferred from oxygen atoms of two carbonyl hydroxyl groups and negatively charged oxygen atoms of two deprotonated carbonyl hydroxyl groups of two alginate chains. The coordination number of the central Cu²⁺ ions in copper alginate is 4. It can be concluded that the vacant site on the active catalysis resulted from the distorted tetragonal configuration that was caused by a crimped chain of the alginate molecule. HSO ₃ ^– produced primary free-radical hydrogen by a coordination catalysis mechanism and vinyl acetate (VAc) polymerization by a free-radical mechanism that is different from polymerization initiated by a CuCl₂–Na₂SO₃–H₂O oxidation–reduction system. The induction period for VAc polymerization is 90 s and the yield is 82%. The M _w, M _n, and M _w/M _n of poly(vinyl acetate) (PVAc) were found to be 1.23×10⁶, 2.27×10⁵, and 4.51, respectively.     

In situ electropolymerized polyaniline–polyacrylonitrile composite film for the construction of a polyphenol oxidase-based biosensor

Polyaniline–polyacrylonitrile composite films prepared by in situ electropolymerization of aniline on polyacrylonitrile-coated platinum electrode were used to immobilize polyphenol oxidase forming an enzyme biosensor. The novel polyphenol oxidase-based biosensor exhibited high sensitivity, low background and excellent stability, which showed no loss of activity after 100 consecutive measurements and intermittent usage for six months with storage in a phosphate buffer at 4 °C. The construction parameters of the enzyme electrode were optimized. The influences of pH and temperature on the biosensor response were explored. The sensitivities of the enzyme electrode for catechol, phenol, p-cresol and m-cresol were 2.03, 0.96, 1.38 and 1.5 A M^–1 cm^–2 respectively.     

Electron donors in carbocationic polymerization

Summary Low molecular weight (¯M_n 900–5000) narrow molecular weight distribution (MWD; ¯M_w/M_n = 1.1–1.2)tert.-chlorine telechelic polyisobutylenes (PIBs) have been synthesized by the use of thetrans-2,5-dimethyl-2,5-diacetoxy-3-hexene (DiOAcDMeH₆)/BCl₃ initiating system in the presence of the electron donor (ED) dimethyl sulfoxide (DMSO) in methyl chloride diluent at –30°C. The living character of the polymerization was demonstrated by linear M_n versus W_p (weight of polymer) plots starting at the origin with the slope of 1/[I_o] (where [I_o] = initiator concentration). DMSO reduces the overall rate of polymerization, however, it increases the initiator efficiency (I_eff) to 100%. The number averagetert.-chlorine end functionality is -F_n=1.97±0.04, by¹H NMR spectroscopy. Polymerization mechanistic details are discussed. This is the first time narrow MWDtert.-chlorine telechelic PIB has been prepared close to the reflux temperature of methyl chloride.Paper XXVII in the series on Living Carbocationic Polymerization. For paper XXVI see Kaszas et al., J. Macromol. Sci. Chem. to appear (1989)     

The use of model polyisobutylene networks to study strain-induced crystallization

Summary Model elastomeric networks were prepared by trifunctionally end linking hydroxyl-terminated chains of polyisobutylene having number-average molecular weights in the range 10^–3M_n = 2.4 – 10.7 g mol^–1. Their stress-strain isotherms in elongation at 25°C in the unswollen state showed significant increases or upturns in modulus at high elongations, due to strain-induced crystallization. Increase in degree of cross-linking (decrease in M_n) was found to decrease the elongation required to initiate crystallization and the maximum extensibility, but to increase the magnitude of the upturn in modulus.     

Living carbocationic polymerization

The living continuous polymerization of isobutylene initiated by a bifunctional initiator, i.e., 2,4,4,6-tetramethyl-heptane-2,6-diacetate·BCl₃ complex, in CH₂Cl₂ and C₂H₅Cl diluent in the –12 to –20°C range is described. Experimental conditions have been found under which rather narrow molecular weight distribution ,-tert.-chloro-ended polyisobutylenes of theoretical M_n and I_eff=100% can be continuously prepared in a tubular reactor in a homogeneous system (in C₂H₅Cl at –12°C). System heterogeneity tends to increase the molecular weights, decrease the I_eff, and increase the ¯M_w/¯M_n.     

The effect of the type of electric current on the cathodic corrosion of aluminium

A comparative experimental study on the cathodic corrosion of aluminium in 0.52 M sodium chloride distilled water solutions is carried out. The electrolysis is conducted using a single half-cycle rectified, direct or industrial frequency current. Characteristic relationships concerning the cathodic corrosion are noted. Attention is drawn to the higher rates of cathodic corrosion observed on electrolysis with single half-cycle rectified current which is combined with lower energy costs.Nomenclature w _k1 cathodic corrosion rate for direct current electrolysis (g s^–1 m^–2) - w_k2 cathodic corrosion rate for single half-cycle rectified current electrolysis (g s^–1 m^–2) - w _a anodic dissolution rate (g s^–1 m^–2) - w _F theoretical Faradaic dissolution rate (g s^–1 m^–2) - w dissolution rate for alternating current electrolysis (g s^–1 m^–2) - j electric current density (A m^–2)     

Physico-Chemical Features and Catalytic Activity of Sulfated Zirconia Prepared by Sol–Gel Method. The Role of the Solvent Evaporation Step

ZrO₂–SO₄ powders have been prepared by following a single-step sol–gel preparative route using zirconium propoxide as the starting compound. Sulfuric acid was employed both as the sulfating agent and as the catalyst of the polycondensation reaction in the gel formation. Two different series of dried precursors were obtained by either evaporating the solvent in an oven at 100°C (xerogels) or in supercritical conditions (aerogels). All the samples were calcined at three temperatures (470, 550, and 630°C) for the same time length (5 h). The powders were characterized for phase composition–crystallinity, surface area–porosity, sulfur content and surface state (XPS). The catalytic activity of the calcined samples was tested in the isomerization of n-butane in a continuous system at 150°C in absence of H₂ and 250°C in presence of H₂. The role played by the conditions of the solvent elimination, at the end of the sol–gel reaction, in affecting the physico-chemical and catalytic properties of the powders is discussed.