Isoprene Polymerization by Butyllithium in Cyclohexane. II. Propagation Reaction

The kinetics of the propagation reaction in the polymerization of isoprene initiated by n-, sec-, or t-butyllithium, in the absence or in the presence of the three corresponding lithium butoxides, are studied in the two possible major cases. In the first case, the propagation takes place without simultaneous initiation; the reaction is then first-order versus the monomer concentration and one-sixth-order versus the polyisoprenyllithium concentration. The lithium butoxides decrease the propagation rate, but the effect is not very dependent on the nature of the butoxide. In the second case, the presence of the initiator decreases the propagation rate in a manner which depends on the concentrations of the reactants and on the nature of the initiator. The effect of the lithium butoxide is not simply additive. Depending on the relative concentrations, a synergistic effect may be observed. It is suggested that the active species are chiefly ion pairs of unassociated polyisoprenyllithium. Ion pairs from associated molecules may have limited activity.     

Electron spin resonance studies on radiation graft copolymerization in polyethylene. II. Grafting initiated by allyl radicals trapped in irradiated polyethylene

The regions trapping allyl radicals in irradiated polyethylene and the reactivity of the radicals with various monomers have been studied by electron spin resonance. Most of the allyl radicals are trapped in defects or surfaces of the crystallite, and only 10% of the radicals are trapped inside the crystallites. Since the reactivity of the allyl radicals depends on whether they come in contact with reactive monomers, the rate of reaction is related to the concentration of the monomers. When grafting reactions are initiated by allyl radicals, the rate of initiation is rapid and the rate of termination at the initial stage is also very fast. Consequently the yield of grafting increases at the initial stage but soon levels off, which is in contrast to the grafting behavior with alkyl radicals.     

城市生活垃圾焚烧飞灰重金属的浸出特性

对用流化床焚烧炉混烧垃圾和煤的布袋飞灰进行了重金属的TCLP(Toxicity Characteristic Leaching Procedure)浸出特性实验，探讨了液固比、初始pH值及浸出时间对飞灰中重金属Pb、Cr、Cd、Ni、Cu、Zn的浸出影响。结果表明，重金属的浸出量都随着液固比的增加而增加，其中Cr、Cu一般呈上升趋势，Cd、Ni、Zn在液固比大于20时曲线变化较平缓，Pb的浸出规律比较特殊，有一个明显的波峰和波谷。重金属在浸取液的pH≤2.90时的浸出浓度远远大于pH≥4.03时的浸出浓度。Pb、Cr、Zn随着浸出时间的增加，浸出浓度下降，而Cd、Ni上升，Cu是先上升后下降。在液固比、初始pH值及浸出时间这三个影响因素中，pH值对重金属的浸出影响较大，重金属在酸性环境下较易浸出。     

The changes in particle charge distribution during rapid growth of particles in the plasma reactor

The changes in particle charging were investigated during the rapid growth of particles in the plasma reactor by the discrete-sectional model and the Gaussian charge distribution function. The particle size distribution becomes bimodal in the plasma reactor and most of the large particles are charged negatively, but some fractions of small particles are in a neutral state or even charged positively. As the particles accumulate in the plasma reactor, the amount of electrons absorbed onto the particles increases, while the electron concentration in the plasma decreases. As the mass generation rate of small particles (monomers) decreases or as the initial electron concentration increases, the electron concentration in the plasmas increases and the particle charge distribution is shifted in the negative direction and the fraction of particles charged negatively and the average number of electrons per particle increase. With the decrease in monomer diameter, the electron concentration decreases in the beginning of plasma discharge, but, later, increases. For high mass generation rate of monomers or for low initial electron concentration or for small monomer diameter, the fraction of particles in a neutral state increases and the particle size distribution becomes broader.     

Kinetics of copolymerization—II. Kinetic investigation of the polymerization of methyl acrylate in solution

The kinetics of methyl acrylate polymerization initiated by azobisisobutyronitrile were investigated in dimethylformamide at 40–60. The polymerization was 1/2 order with respect to initiator; the rate of initiation was independent of the initial concentration of monomer. The rate and the overall rate constant of polymerization strongly depend on the medium: the overall rate constant decreases with increase of solvent concentration. The solvent dependence of overall rate constant can adequately be described by the hot radical theory.     

The Kinetics and Mechanism of the Thermal Dehydrochlorination of Poly(vinyl Chloride)

Poly(vinyl chloride) degrades thermally by an acceleratory reaction in which the rate of hydrogen chloride evolution is slow at the beginning, increases with time (passing through a maximum), and then decreases. A kinetic model based on the zipper mechanism shows excellent agreement with observed data from the initial to the final stages of each dehydrochlorination. Hydrogen chloride is shown to be essential for the initiation of zip chains and may or may not be essential for the zip reaction. When hydrogen chloride is removed in a stream of inert gas, as it is in some tests purported to study the kinetics of degradation, the initiation of zip chains is significantly inhibited. The zip reaction, once it has been initiated, is not inhibited or stopped even by long exposure to atmospheric conditions.     

Sterically stabilized emulsion polymerization of styrene: Pseudo‐semicontinuous approach

The sterically stabilized emulsion polymerization of styrene initiated by a water‐soluble initiator at different temperatures has been investigated. The rate of polymerization (R_p) versus conversion curve shows the two non‐stationary‐rate intervals typical for the polymerization proceeding under non‐stationary‐state conditions. The shape of the R_p versus conversion curve results from two opposite effects—the increased number of particles and the decreased monomer concentration at reaction loci as the polymerization advances. At elevated temperatures the monomer emulsion equilibrates to a two‐phase or three‐phase system. The upper phase is transparent (monomer), and the lower one is blue colored, typical for microemulsion. After stirring such a multiphase system and initiation of polymerization, the initial coarse polymer emulsion was formed. The average size of monomer/polymer particles strongly decreased up to about 40% conversion and then leveled off. The initial large particles are assumed to be highly monomer‐swollen particles formed by the heteroagglomeration of unstable polymer particles and monomer droplets. The size of the “highly monomer” swollen particles continuously decreases with conversion, and they merge with the growing particles at about 40–50% conversion. The monomer droplets and/or large highly monomer‐swollen polymer particles also serve as a reservoir of monomer and emulsifier. The continuous release of nonionic (hydrophobic) emulsifier from the monomer phase increases the colloidal stability of primary particles and the number of polymer particles, that is, the particle nucleation is shifted to the higher conversion region. Variations of the square and cube of the mean droplet radius with aging time indicate that neither the coalescence nor the Ostwald ripening is the main driving force for the droplet instability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 804–820, 2003     

烷基聚葡糖苷微乳液中脂肪酶催化的酯合成反应动力学

在烷基聚葡糖苷C10G1．54／正丁醇／环己烷／磷酸盐缓冲液体系形成的油包水微乳液中,研究了在较高底物浓度下,脂肪酶催化正己酸和正丁醇的酯合成反应动力学及其影响因素。结果表明,在正己酸的初始浓度CHA^0较小时,反应初速率V0随正己酸浓度增大而增大,但随正丁醇表观浓度增大而减小;在CHA^0较大时,反应初速率V0随正丁醇表观浓度增大而增大,但随正己酸浓度增大而减小．在正己酸和正丁醇摩尔浓度之比为3．0左右反应速率最大．这些实验结果与传统的米氏反应不符,为此,从界面膜的构成,尤其是两种底物在界面膜上的分布情况人手进行了探讨．考察了C10G1.54浓度、正丁醇浓度和两者总浓度等对反应初速率V0的影响．     

Copolymerization of styrene and diethyl fumarate with ZnBr2. IV. Comparison between photoinitiation and electroinitiation

A comparative analysis of photoinitiation and electroinitiation can help elucidate initiation processes in donor-acceptor charge-transfer copolymerization. The technique has been applied to the zinc bromide-catalyzed copolymerization of styrene and diethyl fumarate in methanol. The photocopolymer product was analyzed by GPC, NMR, and elemental analysis. The results showed that 1:1 copolymers were formed initially, but changes occurred in both the kinetics and products after the early stages of the reaction. Significant correlations found between the two initiation methods included the initial kinetic order with respect to the initiating process and the effect on product yield of equivalent increases in total initiation energy. The limiting value of zinc bromide for both initiation methods was found to be the same. The data obtained support the contention that the copolymerization proceeds through a donor–acceptor process and that photoactivation of the preformed complex, inducing electron transfer, is a likely initiation process.     

Theoretical depolymerization kinetics. IV. Effect of a volatile fraction on the degradation of an initial “most probable” polymer

The effect of volatilization of molecules larger than monomer has been introduced into the solution of the Simha, Wall, and Blatz kinetic equations for the degradation of a high polymer with an initial “most probable” distribution. Equations describing the rate of sample weight and average molecular weight change result. They differ from the previous “most probable” equations primarily in the presence of an additive term representing the random splitting near the chain ends due to bond scission or transfer attack. Equations are also obtained for the rate of formation of each volatile species and hence the product distribution. The effect of volatilization of larger fragments is discussed in detail for the special case of random scission initiation. The product distribution is discussed for two special cases.     

Ultrasonic degradation of polysilane polymers

The degradation of four polysilanes in solution irradiated by ultrasonic waves has been studied by measurements of reduced viscosity and dynamic mechanical behavior. In all cases ultrasonic degradation occurs. The ultrasonic waves cause the average molecular weight to decrease and the molecular-weight distribution to become narrower in a relatively short period. The degree and rate of degradation are related to the intensity of the ultrasonic waves. In addition, the degree of degradation decreases with increasing polymer concentration and the rate increases with increasing initial molecular weight of the polysilane. After irradiation, the molecular weights of polysilanes tended to the same value from various initial values.     

Effect of emulsion drop-size distribution upon coalescence in simple shear flow: a population balance study

A population balance is used to examine the effect of the shape of the initial drop-size distribution of an emulsion upon its short and long-time evolution in simple shear flow. Initial distributions that are monodisperse, multidisperse, lognormal, bimodal, multimodal, and step functions are considered. At short times, it is shown that the rate of coalescence decreases by up to 25% for step distributions and up to 75% for lognormal distributions as the width of the distribution increases. Bimodal, multidisperse and multimodal distributions show intermediate decreases in the rate of coalescence, between these two values, with increases in the distribution width. Furthermore, it is found that the initial rate of coalescence is strongly dependent upon the presence of large drops. As the number fraction of large droplets within the distribution increases, the rate of coalescence also increases. At long times, all distributions move toward an asymptotic distribution shape in which the frequency of drops decreases algebraically with drop diameter at small drop diameters, and decreases exponentially with drop diameter at large drop diameters. Though portions of each distribution showed the expected asymptotic scaling behavior at long times, each asymptotic distribution nevertheless retains 'fingerprints' of the respective initial distribution. Overall, the rate of coalescence for a system is bounded by the initial rate, which is a function of the initial distribution shape, and the asymptotic rate, which is dependent upon the long-time scaling behavior. Finally, it is shown that the resolution with which the drop-size distribution of an emulsion is experimentally measured can have a significant effect upon predicted rates of coalescence.     

Kinetics and mechanism of emulsifier-free emulsion polymerization. III. Particle growth mechanism of seeded styrene/potassium persulfate system

For seeded emulsifier-free emulsion polymerizations of styrene/potassium persulfate (KPS)/water system using the three sizes of seeds: 1020, 1620, and 1923 Å, analysis on the data of conversion and MWD suggests a shell region polymerization mechanism for the particle growth period as the particle diameter is larger than about 1500–2000 Å. The shell region has thickness of about 100 Å. The occurrence of shell region polymerization is attributed to the higher average number of radicals per particle (n ? 2?7) for the large particle, causing the polymer radicals (with the sulfate ends anchoring on the particle surface) to be terminated by combination at lower MW. Thus, the radical ends have no chance to arrive at the core of the particles. As the smallest seed is used, the rate of polymerization is of zero order, the same as in the conventional emulsion polymerization. MW of the polymer produced in the cases, in which the shell region polymerization occurs, increases with conversion in the entire process, different from the conventional case in which the MW increases first up to about 60% conversion and then decreases. © 1992 John Wiley & Sons, Inc.     

Energy transfer of highly vibrationally excited naphthalene. III. Rotational effects

The rotational effects in the energy transfer between Kr atoms and highly vibrationally excited naphthalene in the triplet state were investigated using crossed-beam/time-sliced velocity map ion imaging at various translational collision energies. As the initial rotational temperature changes from less than 10 to approximately 350 K, the ratio of vibrational to translational (V-->T) energy transfer cross section to translational to vibrational/rotational (T-->VR) energy transfer cross section increases, but the probability of forming a complex during the collisions decreases. Significant increases in the large V-->T energy transfer probabilities, termed supercollisions, at high initial rotational temperature were observed.     

Alkaline Activation of Metakaolin An Isothermal Conduction Calorimetry Study

The alkaline activation of metakaolin leads to high mechanical performance inorganic polymers. A JAF conduction calorimeter was used to follow the reaction of metakaolin with NaOH solutions. The alkaline activation of metakaolin to yield a cementitious material is an exothermic process involving three steps: an initial and very fast process of dissolution, which is strongly exothermic, followed by an induction period in which the heat exchange rate decreases, and finally an exothermic step of reaction reactivation in which cementitious materials precipitate and after which the heat exchange rate decreases. The calorimetric curves lead to the following findings: - The induction period is lengthened as the NaOH solution concentration and the liquid percentage increase. - The induction period is shortened as the temperature increases. - The total heat increases as the liquid percentage and the NaOH concentration increase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydroxypropyl cellulose (HPC)-stabilized dispersion polymerization of styrene in polar solvents: Effect of reaction parameters

Dispersion polymerization of styrene in polar solvents in the presence of hydroxypropyl cellulose (HPC) produces latex particles from ca. 1 to 26 μm depending on reaction parameters. Increasing the initiator concentration or temperature decreases the molecular weight, but increases the particle size and breadth of the size distribution. The decrease in molecular weight with increasing R_i, caused by larger initiator concentration or higher temperature, is expected based of fundamental kinetic relationships. The inverse correlation between size and rate of initiation is rationalized by polarity (stabilizing ability) of the grafted HPC-polystyrene formed in situ. High polar HPC-g-PS, which contains shorter graft polystyrene chain, stabilizes particles less effectively and this leads to larger particles. The primary influence of initial styrene concentration is a solvent effect: larger particles are obtained at high styrene concentration due to high solubility of polystyrene during the initial part of the reaction. The influence of the molecular weight of HPC is to change the polarity of the HPC-g-PS stabilizer. Comparison of particle growth of three critical polymerization systems suggests that the favorable continuous-phase solubility parameter for dispersion polymerization of styrene is around 11.6 (cal/mL)^1/2. Too high or too low polarity generates particles with broad size distribution because large particles are formed during the initial stage and nucleation continues as the polymerization proceeds. © 1992 John Wiley & Sons, Inc.     

Influence of fine structure on the pyrolysis of cellulose. III. The influence of orientation

The effects of orientation upon the pyrolysis of cellulose were investigated by using a series of rayon fibers which differed only in orientation. The initial weight loss seen in low-temperature vacuum pyrolysis is due to crosslinking in the less ordered regions and was shown to be a first-order reaction whose rate varies directly with the degree of orientation. The extent of this reaction decreases with increasing orientation and is directly related to the amount of char formed at higher temperatures. The bulk pyrolysis rate increases with increasing orientation. DSC, air pyrolysis rates, and levoglucosan formation were also studied.     

1H NMR study of the kinetics of substituted aniline polymerization. I. Homopolymerization of 2‐methoxyaniline

We studied the kinetics of the oxidative chemical homopolymerization of 2‐methoxyaniline (OMA) in aqueous acid solutions by monitoring OMA depletion with ¹H NMR spectroscopy. We used the same semiempirical kinetic model used for aniline (ANI) homopolymerization to evaluate the experimental data. The reaction kinetics of OMA homopolymerization was similar to that of ANI, although we obtained longer induction and propagation times for OMA. This was attributed to steric hindrance of the bulky methoxy substituent during the coupling reaction. Furthermore, it was suggested that a lower OMA polymerization rate could also be related to a lower concentration of nonprotonated OMA molecules in the reaction solution due to a higher pK_a value for OMA than for ANI. This may also explain the lower OMA end conversion (90%) compared with that of ANI (96%). The OMA end conversion was not influenced substantially by reaction conditions; it was lower than 90% only when high acid or low oxidant (oxidant‐deficient oxidant/OMA ratio) concentrations were applied. Because the oxidant took an active part in polymerization, it markedly influenced the polymerization rate, especially the initiation rate. The OMA initiation and propagation rates increased with increasing oxidant and initial monomer concentrations and with the reaction temperature, but there was no uniform trend in the correlation between the homopolymerization rate and acid concentration. The activation energies of the OMA initiation and propagation were 57 and 10 kJ/mol, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2471–2481, 2001     

Dissipative curve crossing problem. I. High-barrier crossing

Variational approach based on the diabatic variational transition state theory optimization is extended and applied to the calculation of the radiationless transition rate for asymmetric high-barrier normal and inverted crossings. Scaling argument is employed to derive an analytic expression for the renormalized frequency as a function of the asymmetry of the crossing and of the dissipation strength for the particular case of Ohmic dissipation (Debye relaxation). The effect of the asymmetry of the crossing on the physical parameters and on the radiationless transition rate is explored. The effective adiabaticity parameter increases with the increasing asymmetry of the crossing in the normal region and decreases with the increasing asymmetry in the inverted region. The physical behavior of the radiationless transition rate in the normal and inverted regions is qualitatively different in the strong dissipation (Smoluchowski) limit. In the inverted region the rate exhibits stretched exponential decay as a function of the dissipation strength reflecting adiabatic suppression in the strong dissipation limit. The accuracy of the approach decreases with the increasing (decreasing) asymmetry of the crossing in the normal (inverted) region and breaks down in the activationless case.