Synthesis and characterization of polyacrylonitrile grafted with poly(2,6-dimethyl-1,4-phenylene oxide)

Summary Free radical copolymerization of acrylonitrile (AN, M₁) with poly(2,6-dimethyl-1,4-phenylene oxide)--vinylbenzyl ether (PPO-VBE, M₂, _n + 4200g/mol, _w/ _n + 1.04) was performed at 60°C in either a mixture of N,N-dimethylformamide/toluene or tetrahydrofuran, using 2,2-azoisobutyronitrile (AIBN) as initiator. The characterization of the resulting polyacrylonitrile grafted with poly(2,6-dimethyl-1,4-phenylene oxide) (PAN-g-PPO) was performed by 200 MHz ¹H-NMR spectroscopy and solubility.     

Living cationic polymerization of a vinyl ether with a triester pendant

Summary Cationic polymerization of CH₂=CH-O-CH₂CH₂C(COOC₂H₅)₃, a vinyl ether with three pendent esters, initiated by the HI/I₂ system in toluene at –40 °C afforded living polymers with a controlled molecular weight ( = 10³–10⁴) and a narrow molecular weight distribution ( = 1.1–1.2). The number-average molecular weight of the polymers was directly proportional to monomer conversion and the monomer-to-initiator (HI) feed ratio. The polymers obtained with BF₃O(C₂H₅)₂ had a fairly high molecular weight ( 10⁵, 5 × 10⁴) and a broad molecular weight distribution. The triester vinyl ether was similar in reactivity to alkyl counterparts and one order of magnitude more reactive than the corresponding mono- and diester vinyl ethers.     

The influence of total monomer concentration on the “reactivity” of ω-(p-vinylbenzyl ether) macromonomers of poly(2,6-dimethyl-1,4-phenylene oxide) determined from radiacal copolymerization experiments with butyl methacrylate

Summary The influence of the total monomer concentration on the radical reactivity ratio r₁ of butyl methacrylate (BMA) (M₁)--(p-vinylbenzyl ether) macromonomer of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-VBE) (M₂) monomer pair was investigated. For two different molecular weights of the PPO-VBE macromonomer ( , and ), the determined reactivity ratio r₁ decreases with the increase of the macromonomer concentration. Therefore, the reactivity of the macromonomer, 1/r₁, follows the opposite trend. This dependence is due to micelles formation during copolymerization. This microsegregation process partitionates the comonomer concentrations between the bulk of solvent and around the growing chain and therefore, the experimental r₁ is actually a product of the true reactivity ratio r₁ ⁰ and a partition coefficient k.     

Characterization of metal-ion containing polyesters

Summary The glass transition behavior of poly(diethylene glycol-co-succinic acid) (DEGSA) and its complexes obtained in the reaction with MgO have been investigated. The number average molar mass ( ) of the DEG-SA samples prior to complexation was determined by titration of the terminal COOH groups. The glass transition temperature (T_g) was measured as a function of molar mass and Mg²⁺ ion content. The dependence of T_g on obeyed the Fox-Flory relationship. Addition of increasing amounts of MgO to DEG-SA led to a gradual increase in T_g, and a decrease in the heat capacity change (c_p). This behavior is associated with complex formation between COO^-and Mg²⁺. The decrease in c_p is a result of ion-ion and to a lesser extent ion-dipole interactions which lower chain mobility. The common limiting T_g value for the three DEG-SA samples at an Mg²⁺/COO^- ratio of ca. 0.5 approaches T_g,, which is the corresponding T_g of a polymer of infinite molar mass.     

Residence time distributions and reaction kinetics in a fuel cell anode

A method which treats the fuel cell anode as a chemical reactor is developed to predict fuel cell performance. The method is based on experimentally measured residence time distribution parameters and differential cell kinetic data. The apparatus and experimental technique used to obtain the gas-phase residence time distributions are described. Kinetic data obtained from differential cell tests of the electrodes are used to evaluate an empirical rate expression.Axial dispersion model solutions for flow with volume change are obtained, based on the measured Peclet numbers and empirical rate expressions, and compared with experimental data from operating large high-temperature molten carbonate fuel cells. Agreement between the model and the experimentally determined data is very good, but only for low conversions of the fuel.Notation A cross-sectional area, cm² - C concentration of hydrogen. (g mole/cm³) - c=C/C _o dimensionless concentration of hydrogen - D dispersion coefficient cm²/s - d _e equivalent diameter, cm - F Faraday's constant - I total current, A - J current density, mA/cm² - k reaction rate constant, appropriate units - L length, cm - M number of moles - N =D/UL dispersion number - n order of reaction - n _e number of electrons transferred - –r rate of reaction based on volume of fluid, moles of reactant reacted/ cm³ s - S _e surface of electrode, cm² - T absolute temperature, °K - mean residence time, s - U velocity component in Z direction, cm/s - u = U/U ₀ dimensionless velocity - V _a volume of system, cm³ - V operating voltage, V - v volumetric flow rate, cm²/s - fractional conversion, degree of conversion of hydrogen - y mole fraction of hydrogen - Z space coordinate, cm - z =Z/L fractional length Greek letters coefficient of expansion - _m molar density of fuel, g mole/cm³ - overvoltage, V - dimensional variance, s² - ² dimensionless variance - =V_a/v ₀ space time, s     

Correction of the number average molecular weight of hydroxylated liquid polybutadiene as determined by vapor pressure osmometry

Summary Number average molecular weight ( ) determinations of oligomers by vapor pressure osmometry (VPO) requires highly purified samples. As ultraviolet spectroscopy is a convenient technique for accurate evaluation of small concentrations, it was used to determine the concentration of 2,6-di-t-butyl-4-methylphenol antioxidant in commercial hydroxylated liquid polybutadiene in the = 28000–3000 range. The data were used to correct values measured by VPO, allowing the determination of correct molecular weights without previous polymer purification.     

Copper recovery from dilute solutions in the Falling-Film cell

The removal of copper from dilute solutions is examined in electrochemical reactors where the electrolyte flows as a thin film in an inclined channel between a plane plate and a sheet of expanded metal (Falling-Film cell). Copper is recovered as a thin sheet from the plane plate. The results are compared with a known simplified model and the variations of the faradaic yield with the operating conditions are discussed.Nomenclature A _e electrode surface area - b width of inclined channel - C(t) copper concentration at timet - C ₀ initial copper concentration - d interelectrode distance - overall current density - overall limiting current density - overall mass transfer coefficient - L length of the channel - Q _v volumetric flow rate - Q _vl volumetric flow rate per unit of channel width (=Q _v/b) - t time - t _s residence time in the reactor, defined by Equation 1 - mean flow velocity of the liquid film, defined by Equation 2 - V volume of electrolyte in the circuit - V _R reactor volume - v _sn normalized space velocity, defined by Equation 9 - inclination angle with respect to the horizontal - instantaneous faradaic yield - time-averaged faradaic yield - v _e number of electrons exchanged in the electrochemical reaction     

Mark-Houwink-Sakurada coefficients for conventional poly(methyl methacrylate) in tetrahydrofuran

Summary Intrinsic viscosities [] in tetrahydrofuran (THF) at 30°C are reported for ten narrow molecular weight distribution poly(methyl methacrylate) (PMMA) samples covering nearly two orders of magnitude in molecular weight. By combining the viscosity results with absolute weight-average molecular weights determined via low-angle laser light scattering (LALLS) experiments, we have accurately determined the Mark-Houwink-Sakurada (MHS) parameters for this polymer-solvent pair (K=7.56x10⁵ and a=0.731, when [] is in dL g^-1).     

Polymerization of substituted acetylenes by (mesitylene)M(CO)3 (M=W,Mo)

Summary Phenylacetylene could be polymerized by (mesitylene)W(CO)₃ in CCl₄ to give a polymer with 12,000 in ca. 80% yield. UV irradiation was unnecessary unlike the W(CO)₆–CCl₄-h catalyst. The present polymerization did not proceed in toluene. The (mesitylene)W(CO)₃ catalyst afforded high molecular weight polymers from phenylacetylenes bearing bulky substituents (e.g., Me₃Si and CF₃) at the ortho position. The Mo counterpart, (mesitylene)Mo(CO)₃, catalyzed the polymerization of 1-chloro-2-phenylacetylene and 1-chloro-1-octyne to provide high molecular weight polymers . Catalytic amounts of Lewis acids accelerated the polymerization of phenylacetylene by (mesitylene)W(CO)₃, but decreased the polymer molecular weight; this polymerization proceeded not only in CCl₄ but also in toluene.     

Numerical simulation of non-Newtonian jets emanating from a converging cone

The effects of the rheological properties on the fluid motion of non-Newtonian jets emanating from a converging cone have been investigated theoretically. Three typical non Newtonian fluid models have been considered; i.e. the power-law fluid, the modified Bingham ngham fluid and the Oldroyd-B fluid. The effects of five parameters on the flow field are analyzed in detail; these parameters are: the contraction ratio of the radius of the cone far upstream to that at the cone exit L; the converging angle of the cone 6; the power-law index n; the Bingham number Bn and the Weissenberg number We. The Galerkin finite-element method incorporated with the upwind scheme was applied to solve the flow problems numerically. Full Newton iteration was used to solve the flow fields and the free-surface positions of power-law and modified Bingham fluids. However, the free-surface position of the Oldroyd-B fluid has to be updated by kinematic iteration to avoid numerical oscillations.Notation a one-half of the cone gap at the cone exit - Bn Bingham number, Eq. (8) - b radius of the cone far upstream - C_o jet swell ratio, Eq. (2) - D rate of the deformation tensor, Eq. (7) - I unit tensor - L contraction ratio, Eq. (2) - m exponent factor of the modified-Bingham fluid, Eq. (8) - n power-law index - n unit normal vector - p, pressure, dimensional and dimensionless - P_atm environmental pressure - U average fluid speed at the cone exit - v, velocity vector, dimensional and dimensionless - We Weisenberg number, Eq. (9) Greek letters viscosity ratio of polymer to solution - one-half of the jet thickness far downstream - _o Newtonian viscosity or consistency of power law fluid - converging angle, Figure 1 - relaxation time of the Oldroyd-B fluid - _D second invariant of tensor D, Eq. (7) - total stress tensor, Eq. (5) - , stress tensor, dimensional and dimensionless - _E elastic stress tensor, Eq. (9) - _V stress tensor, Eqs. (6), (8) and (9) - _o apparent yield stress     

Mass transfer at the electrodes of the ‘falling-film cell’

In the falling-film cell the electrolyte flows as a thin film in the channel between an inclined plane plate and a sheet of expanded metal which work as electrodes. The present work gives the mass transfer coefficients at both electrodes; the experimental variables are the electrolyte flow-rate, the angle of inclination of the channel and the interelectrode distance. The results allow three different flow regimes to be characterized. At low flow rates, there exists a particular regime where capillary effects are present; in this regime the mass transfer coefficient decreases with increasing flow rate, which is interesting from the point of view of possible industrial electrolytic applications.Nomenclature b width of the inclined channel - D diffusion coefficient - d interelectrode distance - e _m mean film thickness - Grashof number, based ond - Grashof number, based onL - ¯k overall mass transfer coefficient, defined by Equation 9 - L electrode length - Q _v volumetric flow rate - volumetric flow rate per unitQ _vl width of channel - Reynolds number - Schmidt number - Sherwood number, based ond - Sherwood number, based onL - mean velocity of the liquid film - inclination angle of the channel with respect to the horizontal - kinematic viscosity of them electrolyte     

Calculation of piezoelectric constants of poly(vinylidene fluoride)

Summary Piezoelectric constants of poly(vinylidene fluoride) form I crystal have been calculated to give a good agreement with observed values; d₃₃ = –2.5 × 10^–11 C/N (observed: –2 × 10^–11 C/N) and d₃₃ = –2.5 × 10^–13 C/N (observed: ca. 10^–13 C/N). The macroscopic piezoelectric constants have also been calculated using such a model that the piezoelectric crystal form I is embedded in the non-piezoelectric amorphous matrix to be d ₃₁ ^M 0.6 × 10^–11 C/N (at room temperature) and 4.6 × 10^–13 C/N (below glass transition temperature), and d ₃₃ ^M –1.4 × 10^–11 C/N and –0.5 × 10^–11 C/N, respectively, reproducing well the observed temperature dependence of these constants.     

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.     

Living carbocationic polymerization

Summary The living synthesis of ,-di-tert.-chloropolyisobutylene ( ^t -Cl-telechelic PIB) has been accomplished by the use of the sterically hindered bifunctional initiator 1,3-di-(2-methoxy-2-propyl)-5-tert.-butylbenzene (tBu-m-DiCuOMe) in conjunction with BC1₃ coinitiator in CH₃Cl or CH₂Cl₂ diluents at –30°C and –10°C. The living nature of the polymerizations was demonstrated by linear ¯M_n versus W_PIB (g of PIB formed) plots starting at the origin and horizontal N (number of PIB moles) versus W_PIB plots. The molecular weight distributions are narrow (¯M_W/¯M_n < 2.0) and tend to decrease with increasing molecular weights. Number average end functionalities have been quantitated and found to be ¯F_n = 2.0±0.1.     

The performance of porous and gauze electrodes in electrolysis with parabolic velocity distribution

An approximate numerical method for the estimation of the velocity exponent in (small-scale) flow-through porous and gauze electrodes is presented. The method can also be employed to determine if a plug-flow or a parabolic-flow model offers a more reliable representation of the experimental behaviour of the electrode.Nomenclature a cross sectional area of the electrode - B integration parameter (Equations 7 and 8) - c exit active ion concentration, its mean measured value in the case of parabolic flow,c _o its inlet value;c _m its mean value; its mean calculated value in the case of parabolic flow;c ^* dimensionless concentration, equal toc/c _o; mean dimensionless concentration, equal to /c _o - F Faraday's constant - i _L mean limiting current density (geometric-area base) - j proportionality factor (Equation 1) - k _m mass transport coefficient, its mean value - L length of the electrode - n number of electrons involved in the electrode reaction - N ionic flux - r radial coordinate - R _E geometric radius - R limiting degree of conversion - s specific surface area of the electrode (surface per volume) - u linear solution velocity; u_o its maximum (centreline) value; its mean value (=u_o/2) - v volumetric flow rate; its mean value - x transform variable forz - z dimensionless radial distance - velocity exponent for mass transport (Equation 1)     

Living cationic polymerization of styrene by the 1-phenylethyl chloride/tin tetrachloride initiating system in the presence of tetra-n-butylammonium chloride

Summary An initiating system, consisting of 1-phenylethyl chloride, tin tetrachloride, and tetra-n-butylammonium chloride [CH₃CH(Ph)C1/SnCl₄/nBu₄NCl], led to living cationic polymerization of styrene in CH₂Cl₂ solvent at-15°C; typically, CH₃CH(Ph)Cl/SnCl₄/nBu₄NCl=20/100/40 mM for 1.0 M of styrene. The living nature of the process was confirmed by an increase in the number-average molecular weight ( ) of the polymers in direct proportion to monomer conversion and its continuation on supplying a fresh feed of styrene after the polymerization; the observed was close to the calculated value assuming that one molecule of CH₃CH(Ph)Cl yields one living polymer. Throughout these reactions, the polymer's molecular weight distribution (MWD) stayed very narrow ( ), though slightly broadening after the second monomer addition. In the absence of nBu₄NCl, the CH₃CH(Ph)Cl/SnCl₄ system yielded polystyrene with a bimodal MWD where the lower polymer fraction alone was apparently of a long lifetime. Styrene polymerization with the H₂O/SnCl₄ system was also examined, both with and without added nBu₄NCl, and a long-lived propagating species was obtained in the presence of nBu₄NCl.     

On the determination of oxygen potentials and O/M ratios in mixed U-Pu oxides by means of solid state galvanic cells

Measurements of oxygen potential on uranium-plutonium mixed oxides by means of solid state galvanic cells are discussed and compared with precedent data. Discrepancies in the values at low temperature (1000 K) as well as in the versusT slopes are found, which disappear when the samples are thermally cycled. An analysis is performed of this effect, showing that the absence of a good homogeneization of the sample in oxygen and/or in plutonium content can give rise to mixed potentials and hence to erroneous results.     

Living carbocationic polymerization

Summary The efficient synthesis of symmetrical telechelic polyisobutylenes carrying CH₂C(CH₃)₂Cl groups at either end of the molecule, , has been accomplished by rapid living polymerization using aromatic di-tert.-ether/BCl₃ initiator system in CH₃Cl at –70°. The living nature of the polymerization was demonstrated by linear M_n versus amount of PIB formed (W_PIB) plots starting at the origin. The effect of temperature and solvent composition (polar/nonpolar) on the polymer structure has been investigated. Undesirable indanyl end groups which form during polymerizations carried out at –30° and –50°C can be eliminated by decreasing the temperature to –70°C. The apparent activation energy differences have been determined in the –30 to –70°C range at different polar/nonpolar solvent compositions: E_a of decreases from 2.6 to 1.0 kcal/mole by decreasing the polarity of the medium from 100% CH₃Cl to a 60/40 v/v CH₃Cl/hexanes mixture.     

Phase transfer catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of a terminating comonomer phenol: 2,4,6-tri-tert-butylphenol or 4-bromo-2,6-di-tert-butylphenol

Summary This paper describes the phase transfer catalyzed (PTC) polymerization of 4-bromo-2,6-dimethylphenol (1) in the presence 2,4,6-tri-tert-butylphenol (2) or 4-bromo-2,6-di-tert-butylphenol (4). The polymerization of 1 in the presence of 2 at a 1/2 molar ratio of 3/1 led to poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with _n of 13400 g/mol at a yield of 85%. In contrast, the polymerization of 1 in the presence of 4 at 1/4 molar ratios of 5/1 and 10/1 did not produce any methanol insoluble PPO fraction when 4 was added at the beginning of the polymerization. However, PPO with _n + 1600 to 2400 g/mol were obtained when 4 was added to the polymerization system after 0.5 h and respectively 2.0 h after the homopolymerization of 1 was started. A radical-anion mechanism is proposed to account for these polymerization results.     

Influence of molecular weight on the crystallization of poly(vinylidene fluoride)

Five samples of Poly (vinylidene fluoride) with a molecular weight from 45,000 to 260,000 were analyzed by means of FT-IR spectroscopy in order to study the influence of molecular weight on the crystallization process. The spectra of films obtained from methylethylketone solutions revealed the prevalence of form II () in the case of lower and of form III () in the higher molecular weight samples. The amount of form III was found to increase as the Mv decreased and as annealing temperatures increased. The deconvolution technique of vibrational spectra allowed detection of small amounts of other forms accompanying the prevailing one.