Polyisobutylene-containing block polymers by sequential monomer addition

Novel poly(acenaphtylene-b-isobutylene-b-acenaphtylene) (PAc-PIB-PAc) triblock copolymers exhibiting thermoplastic elastomer (TPE) properties have been prepared. The synthesis involved the addition of acenaphtylene (Ac) to living polyisobutylene dications (PIB) obtained by living isobutylene (IB) polymerization induced by the dicumyl methyl ether (DiCumOMe)/TiCl₄ initiating system at-80°C. The triblocks contain very short polyacenaphtylene (PAc) blocks (M_n9,000) and consequently yield very soft, low modulus TPEs. Efforts to develop conditions for the living carbocationic polymerization (LCPzn) of Ac have failed.For Part VIII of this subseries see J. P. Kennedy, S. Midha, B. Keszler: Macromolecules (in press)     

New polyisobutylene based model ionomers

Three-arm star polyisobutylene ionomers (¯M_n=8800) with terminal SO₃ M (M=K or Ca²) groups were synthesized and their mechanical properties investigated. Compression molded films displayed high elongations, i.e., -1000% for Ca² ionomers with lower values for the K counterions. Strain induced crystallinity was observed at higher elongations. Mechanical properties in general compared favorably with conventional covalently linked rubbery networks and were comparable and in some cases superior to EPDM-based ionomers carrying randomly distributed SO₃ M groups.For the first two parts see Proceedings, 28th IUPAC Macromolecular Symposium, Amherst, MA, July 11–16, 1982, p. 905 and 906     

Phase transition in swollen gels

Summary The swelling and mechanical behaviour of networks of copolymers of acrylamide, methylenebisacrylamide and sodium 2-(2-carboxybenzoyloxy)ethylmethacrylate (mole fraction of salt x _s =0–0.2) in water-acetone mixtures was investigated. In the range x _s 0.01 phase transition (collapse) was observed, with both the extent of the collapse and the critical acetone concentration in the mixture at collapse, a _c , increasing with increasing concentration of the salt. A comparison between these results and those obtained for networks with a quaternary ammonium salt led to a conclusion that an exchange of the positive charge of the ammonium salt (NCl) for the negative charge of the sodium salt (COONa) in the side chain decreases the critical content of salt necessary for the collapse, X _s ^c , from 0.03 to 0.01, and the collapse takes place at lower concentrations of acetone. The collapse may also take place in a mixed solvent waterethanol; the dependence of network swelling on the concentration of ethanol is roughly the same as that on the concentration of acetone.     

Studies on electrical conductivity of gamma irradiated polyaniline

Summary de electrical conductivity at surface of -irradiated polyaniline (PAn) has been studied. EPR spectroscopic results indicate that the variation of spin concentration is consistent with the increase of _de. Electrical conductivity (_de) versus temperature (T) characteristics of unirradiated and irradiated PAn were performed, which demonstrate that the unirradiated curve can fit to ln_deT₁, while the irradiated curve fit to ln_deT_1/4.     

Redox 1∶1 alternating copolymerization of cyclic acyl phosphonte with 4,4′-diphenoquinones

Summary A cyclic phosphonite(1) was copolymerized with 4, 4-diphenoquinones (2a–2c) to give 11 alternating copolymers (3a–3c) consisting of a carboxylic acid ester and a triaryl phosphonate ester. Copolymerization took place without added initiator. During the reaction 1 was oxidized whereas 2 was reduced (redox copolymerization). A mechanism involving a genetic zwitterion intermediate (4) is proposed for the copolymerization.     

Synthesis of ternary Li–Mn–O phase at a temperature of 260 ∘C and electrochemical lithium insertion into the oxide

A lithium–manganese oxide, Li _x MnO₂ (x=0.30.6), has been synthesized by heating a mixture (Li/Mn ratio=0.30.8) of electrolytic manganese dioxide (EMD) and LiNO₃ in air at moderate temperature, 260 C. The formation of the Li–Mn–O phase was confirmed by X-ray diffraction, atomic absorption and electrochemical measurements. Electrochemical properties of the Li–Mn–O were examined in LiClO₄-propylene carbonate electrolyte solution. About 0.3 Li in Li _x MnO₂ (x=0.30.6) was removed on initial charging, resulting in characteristic two discharge plateaus around 3.5V and 2.8V vs Li/Li⁺. The Li _x MnO₂ synthesized by heating at Li/Mn ratio=0.5 demonstrated higher discharge capacity, about 250mAh (g of oxide)^–1 initially, and better cyclability as a positive electrode for lithium secondary battery use as compared to EMD.     

Elucidating the mechanism of carbocationic polymerization of α-methylstyrene

Summary The polymerization of -methylstyrene (MeSt) using the H₂O/SnCl₄ initiating system and ethyl chloride solvent has been investigated over the temperature range from –40° to –122°C in the presence and absence of the proton trap 2,6-di-tert-butylpyridine (DtBP). Arrhenius (In ¯M_n versus 1/T) plots obtained with poly (methylstyrene) (PMeSt) samples prepared in the absence of DtBP reveal the existence of two sharply defined temperature regimes (see Figure 1): at higher temperatures from –40 to –86°C, the slope of the Arrhenius plot yields H_{M n} = –4.90±0.25 kcal/mole whereas at lower temperatures, from –86° to –122°C,H_{M n} = –0.3 kcal/mole. With PMeSt samples prepared in the presence of DtBP the H_{M n} obtained for the higher temperature regime increases to –1.67 ± 0.20 kcal/mole whereas the H_{M n} reflecting the lower temperatures remains the same as that obtained in the absence of DtBP. These observations are readily explained by postulating a change in mechanism at –86°C: Evidently the ¯M_n of PMeSt is determined over the higher temperature regime by chain transfer to monomer which is frozen out at lower temperatures where termination becomes ¯M_n determinant. In the absence of DtBP chain transfer to monomer is operative which leads to the higher Arrhenius slope over the higher temperature regime; however, over the lower temperature regime where chain transfer is absent and termination is ¯M_n controlling, the Arrhenius slope remains unchanged. Evidence obtained from a Mayo plot (negligible intercept in the 1/¯M_n versus 1/[MeSt]_o plot, Figure 2) with samples prepared at –92°C, corroborate this postulate. Molecular weight dispersities (¯M_W/¯M_n) as a function of temperature have been determined in the presence and absence of DtBP (Figure 3). The proton trap affects ¯M_W/¯M_n only over the higher temperature regime which also suggests that chain transfer to monomer is frozen out at –86°C and that the polymerization becomes termination dominated at low temperatures.     

Electrochemical behaviour of viologen-cyclodextrin inclusion complexes. The case of non-alkyl group substituted viologen

The electrochemical behavior of non-alkyl substituted viologen, 4,4-dibenzyl bipyridinium (BzV), 4,4-dicyanophenyl bipyridinium (CyV) and -,-,-cyclodextrin (, , -CD) was studied using cyclic voltammetry and a spectroelectrochemical method. It was found that BzV and Fe(CN) ₆ ^4– formed a charge-transfer (CT) complex with a ratio of 21 and the colour of the solution faded with the addition of an electrolyte. This behaviour is the same as in then-heptyl viologen and ferrocyanide system [1]. BzV, -CD and -CD formed an inclusion complex only in the reduced state, whilst BzV and -CD formed an inclusion complex in both the oxidized and the reduced state. An EC scheme in which a chemical reaction follows an electrochemical reaction was considered to predominate in the BzV and -, -CD systems, while a CE scheme in which a chemical reaction preceded an electrochemical reaction predominated in the BzV and -CD system. On the other hand, CyV was found to form an inclusion complex with -, -, -CD in both the oxidized and the reduced states. therefore a CE scheme was considered to predominate in the CyV--, -, -CD systems.     

Critical solution point and chain dimension of branched-polystyrene solutions

Summary Critical solution point and chain dimension were measured for branched polystyrene(BPS) in solution as a function of molecular weight(M) and compared with those for linear polystyrene(LPS). The critical concentration _c of BPS was quite different from that of LPS at a fixed M, but the same at a fixed overlap-concentration ^*, i.e., plots of _c vs. ^* fall on a single straight line for both BPS and LPS (gf_c ^*). Reduced critical temperature _c defined by gt_c=(–T_c)/ [T_c: critical temperature, : the -temperature] was related to _c as _{c c} ² for BPS, whereas _{c c} for LPS.     

A model of the electrochemical behaviour within a stress corrosion crack

A mathematical model of the electrochemical behaviour within a stress corrosion crack is proposed. Polarization field, crack geometry, surface condition inside the crack, electrochemical kinetics, solution properties and applied stress can be represented by the polarization potential and current, the electrochemical reactive equivalent resistance of the electrode, the change in electrolyte specific resistance and surface film equivalent resistance, respectively. The theoretical calculated results show that (i) when anodic polarization potential is applied, the change in the crack tip potential is small; (ii) when cathodic polarization potential is applied, the crack tip potential changes greatly with the applied potential; (iii) the longer the crack, the smaller the effect of the applied potential on the crack tip potential in both anodic polarization and cathodic polarization conditions. The calculated results are in good agreement with previous experimental results.Notation coordinate, from crack mouth (on the metal surface) to crack tip (cm) - y y = s _L L/(s ₀ – s _L) + L – , function of (cm) - y ₀ y ₀ = s _L L/(s ₀ – s _L) + L (cm) - V polarization potential (V) - galvanic potential of electrode (V) - ₁ galvanic potential of electrolyte (V) - t sample thickness (cm) - w sample width (cm) - S _L crack tip width (cm) - S _o crack mouth width (cm) - L crack length (cm) - s() crack width at position (cm) - _lo specific resistance of electrolyte, as a constant ( cm) - _s specific resistance of metal ( cm) - (, y) specific resistance of electrolyte, varies with potential and crack depth ( cm) - R _b (, y) electrochemical reactive equivalent resistance of electrode, varies with potential and crack depth () - R ₁ electrolyte resistance () - R _s metal resistance () - r(, y) surface film equivalent resistance, varies with potential and crack depth () - r _o surface film equivalent resistance, as a constant () - I _o total polarization current (A) - I net polarization current from integrating 0 to in Fig. 2 (A) - polarization overpotential (V) - _a anodic polarization overpotential (V) - _c cathodic polarization overpotential (V) - Euler's constant     

Initiation of living polymerization of isobutyl vinyl ether by the “H2O”/n-Bu4NTiCl5 system

Summary Living carbocationic polymerization (LCPzn) of isobutyl vinyl ether (IBuVE) is readily initiated by adventitious moisture (H₂O) in the presence ofn-Bu₄NTiCl₅ in CH₂Cl₂ solvent at-20 °C to yield high molecular weight polymers (up to 100,000 g/mole) with narrow molecular weight distributions . The number of macromolecules remains constant and reflects the number of H₂O molecules in the charge. Thede facto initiator is most likely HCl formedin situ by the partial hydrolysis ofn-Bu₄NTiCl₅. Surprisingly the overall polymerization rates obtained in the presence of purposely added initiator, MeCH(Oi-Bu)Cl, were lower than in the absence of it,i. e., with initiator free system. Experiments carried out in the presence of the proton trap, 2,6-di-tert-butylpyridine (DtBP), and alcohols were analyzed to explain the findings. The observed rates may be explained by reactions between H₂O and the various ingredients in the system prior to initiation.     

Dynamic mechanical properties of crosslinked polyisoprene under deformation

Summary Molecular motions of elastomers under deformations were observed through dynamic mechanical measurements. Composite master curves of dynamic moduli E and E and loss tangent tan over a wide range of frequency and in a state of elongation were obtained by the time-temperature superposition procedure. It is found that both moduli increase with strain, . The slope of the dispersion curve of E become more gradual with the increase in , while that of E is almost unchanged. The increment of E is generally larger than that of E, which does not agree with the N. W. Tschoegl prediction, E ^* ()=f() E _o ^* (), where E ^* () and E _o ^* () are complex moduli at the strain of and O, respectively, and f() is the function of only . The difference in the strain dependence of E from E was found to correspond to the strain dependence of the equilibrium modulus.     

Rate of radical polymerization of N,N-dimethylaminoethyl methacrylate in cyclohexane

Summary Anions of propene, isobutylene and cycloheptatriene have been prepared using Lochmann's Base. Star polymers in the form of one arm star, two arm star and three arm star polymers of styrene have been synthesized from the allyl anion (2), 2-methylenepropylenyl dianion (4) and the cycloheptatrienyl trianion (6) respectively, with acid end groups by quenching the living polymers with carbon dioxide. The number average molecular weight has been determined by stoichiometry, HPSEC and end group analysis by titration.     

Molybdenum nitride for the direct decomposition of NO

The physico-chemical properties of passivated -Mo₂N have been investigated. The material showed high activities for NO direct decomposition: nearly 100% NO conversion and 95% N₂ selectivity were achieved at 450C. The amount of O₂ taken up by -Mo₂N increased with temperature rise and reached 3133.9 molg^–1 at 450C; we conclude that there formation of Mo₂O_xN_y occurred. This oxygen-saturated -Mo₂N material was catalytically active: NO conversion and N₂ selectivity were 89 and 92% at 450C. We found that by means of H₂ reduction at 450C, Mo₂O_xN_y could be reduced back to -Mo₂N and the oxidation/reduction cycle is repeatable; such a behaviour and the high oxygen capacity (3133.9 molg^–1) of -Mo₂N suggest that -Mo₂N is a promising catalytic material for automobile exhaust purification.     

The effect of support structure on CO2 hydrogenation over a rhodium catalyst supported on niobium oxide

The hydrogenation of CO₂ was investigated over a rhodium catalyst supported on niobium oxide at atmospheric pressure. Niobium oxide was prepared by the hydrolysis of niobium chloride and its crystallitic structure was controlled by calcination temperature. It was found that the activity was lower but the selectivity of C₂₊ hydrocarbons was higher for the and forms than for the and forms of the niobium oxide.     

Catalytic oxidation of methanol to methyl formate over silver – a new purpose of a traditional catalysis system

Catalytic reaction was performed in the unregarded temperature region over silver catalysts with long catalytic lifetime for the conversion of methanol to methyl formate. O-saturated or O-saturated silver catalysts were studied individually to identify the roles of O, O in the oxidative esterification of methanol over an unsupported polycrystalline silver catalyst. A synergic process is proposed based on the coexistence of -oxygen species and -oxygen species on the surface of polycrystalline silver at about 573 K.     

Musk deer (Moschus moschiferus): Reinvestigation of main lipid components from preputial gland secretion

The qualitative and quantitative composition of the principal lipid constituents of Siberian musk deer (Moschus moschiferus) preputial gland secretion, main odor carriers and potential precursors of odorous substances, was investigated by means of high-performance liquid chromatography. Free fatty acids and phenols (10%), waxes (38%), and steroids (38%) were found to be the main groups of the secretion lipids. Cholestanol (I), cholesterol (II), androsterone (III), ⁴-3-hydroxy-17-ketoandrostene (IV), 5, 3-hydroxy-17-ketoandrostane (V), 5, 3, 17-dihydroxyandrostane (VI), 5, 3, 17-dihydroxyandrostane (VII), and 5, 3, 17-dihydroxyandrostane (VIII) were isolated from the steroid fraction and their structures confirmed by IR, PMR, and mass spectra. 3-Methylpentadecanone (muscone) was not identified among the secretion lipids. Preputial gland secretion stimulated sex behavior of musk deer females.     

Multi-arm star polyisobutylenes

Summary The first synthesis of a multi-arm radial-star polyisobutylene (*-PIB) is described. The synthesis occurred by the addition of excess divinylbenzene (DVB) linking reagent to a living polyisobutylene (PIB) charge i.e., by the arm first method under specific conditions. The radial structure of the *-PIB was proven by determining the molecular weight of a sample by light scattering, then selectively destroying the aromatic polydivinylbenzene (PDVB) core, and finally determining the molecular weight of the surviving alphatic PIB arms. The synthesis strategy, kinetic observations during synthesis, and procedures leading to a representative *-PIB are described. This product whose g/mole with , contained 90.3 mole% (78 wt.%) PIB arms and 9.7 mole% (22 wt.%) aromatic core; thus the number of PIB arms emanating from the core was (number average number of arms)=56 or (weight average number of arms)=110.     

Studies concerning charged nickel hydroxide electrodes I. Measurement of reversible potentials

Reversible potentials (E _R) have been measured for nickel hydroxide/oxyhydroxide couples over a range of KOH concentrations from 0·01–10 M. It is shown that the couples derived from the parent- and-Ni(OH)₂ systems can be distinguished by the relative change in KOH level on oxidation and reduction. In the case of couples derived from the-class of materials a dependence of 0·470 moles of KOH per 2e change is found compared with 0·102 moles of KOH per 2e change for the-class of materials. Couples derived from the- and-Ni(OH)₂ systems can be encountered in a series of activated and de-activated forms having a range of formal potentialsE ₀ . Activated. and de-activated-Ni(OH)₂/-NiOOH couples are found to lie in the range 0·443–0·470 V whilst-Ni(OH)₂/-NiOOH couples lie in the range 0·392–0·440 V w.r.t. Hg/HgO/KOH. It is demonstrated for de-activated,-Ni(OH)₂/-NiOOH couples thatE _R is independent of the degree of oxidation of the nickel cation between states of charge of 25% and 70%. SimilarlyE _R is constant for states of charge between 12% and 60% for activated-Ni(OH)₂/-NiOOH couples. The constant potential regions are considered to be derived from heterogeneous equilibria between pairs of co-existing phases both containing nickel in upper and lower states of oxidation. Differences inE ₀ between the activated and de-activated couples are considered to be related to the degree of order/disorder in the crystal lattice.     

The surface structure and composition of the low index single crystal faces of the ordered alloy Pt3Sn

The surface composition and structure of 111, 100, and 110 oriented single crystals of the ordered alloy Pt₃Sn (Ll₂ or Cu₃Au-type) were determined using the combination of low energy electron diffraction (LEED) and low energy ion scattering spectroscopy (LEISS). The clean annealed surfaces displayed LEED patterns and Sn/Pt LEISS intensity ratios consistent with the surface structures expected for bulk termination. In the case of the 100 and 110 crystals, preferential termination in the mixed (50% Sn) layer was indicated, suggesting this termination to be the consequence of a thermodynamic preference for tin to be at the surface.