Reactivity and mechanism in the cationic polymerization of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate

The cationic polymerization of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate in dichloromethane solution has been studied in some detail. Reactions proved to be highly exothermic, and rates of monomer consumption were measured using an adiabatic calorimetric technique. Termination was deduced to be insignificant during kinetic lifetimes, and $\text{M}\text{?}{}_{\mathrm{n}}$ values in the range 10000–50000 showed chain breaking to occur by transfer mechanisms. Appropriate analysis of conversion/time curves allowed computation of enthalpies of polymerization and rate coefficients for propagation, k_p (obs), under various conditions. Data for k_p (obs) were found to vary with the initial concentrations of initiator and monomer employed, and these dependences are discussed in terms of current theories regarding ion pair/free ion equilibria in nonaqueous solvents. In particular values of 3.6 × 10³ M^?1s^?1 and 4.8 × 10³ M^?1s^?1 at 0° and +10°C respectively for the rate constant for propagation by free poly (p-methoxystyryl) cation have been deduced, and a tentative value of 450 M^?1s^?1 at 0°C has been estimated for the rate constant for propagation by the corresponding hexachloroantimonate ion pairs. These data and the related activation parameters are compared with independent results in the literature. Polymerizations carried out in the presence of excess common ion salt, dimethyl benzyl phenyl ammonium hexachloroantimonate, showed rate depressions far in excess of those predicted by a simple mass law effect, arising possibly as a result of a more dramatic ionic association than simple ion pairing.     

A kinetic study of ‘living’ coordination polymerization of propene with the soluble V(acac)3-Al(i-C4H9)2Cl system

The soluble V(acac)₃-Al(i-C₄H₉)₂Cl system initiated living polymerization of propene at ?78°C affording monodisperse polymers ($\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{= 1.15 ± 0.10}$). A kinetic study (of the living polymerization) was carried out to evaluate the rate coefficients for propagation. The equilibrium constant K_M for a propene monomer coordinated to an active vanadium and the rate constant k_p for a subsequent insertion of coordinated monomer into a living polymer chain were determined and compared with the values for the polymerization of propene with other soluble vanadium-based catalyst systems. The relation between K_M and k_p revealed that a strong interaction between vanadium and propene is unfavourable for the insertion of the coordinated propene into a living polymer chain. The mechanism of an initiation reaction involving alkylation and complexing of V(acac)₃ with Al(i-C₄H₉)₂Cl has been proposed.     

Minimum end time policies for batchwise radical chain polymerization—III: The initiator addition policies

For batchwise radical chain solution polymerization, the minimum end time problem is studied by considering the initiator concentration (or feed rate) and temperature as two control variables. The kinetic model used is based on a general mechanism and involving the gel effect. It is found that the optimal initiator addition policy is to make the rate of initiation constant and rate of conversion nearly constant throughout the entire process. This results in a small variation of $\text{X}$_n and $\text{X}$_w with time and therefore in a nearly constant polydispersity (about 1.6 for styrene/toulene system) in the absence of chain transfer agent. For isothermal case, the initiator concentration should remain constant; analytical expression for temperature and initiator concentration are obtained. For nonisothermal case with high conversion, the temperature increases to a maximum and then drops, while the initiator concentration progresses oppositely. Further calculation shows that the optimal initiator addition processes are more efficient than the optimal processes with one-charge of initiator. Experimental verifications on the isothermal initiator addition policies for the polymerizations of styrene/toluene system show promising. ca*|Author to whom correspondence should be addressed.     

Determination of the transfer constant for copolymerization in the presence of a reactive substrate

Important equations recently presented by Bamford et al.¹, for chain transfer with reactive substrates in copolymerizing systems are analogous to the well-known relationship:

$\text{In}\text{[S]}\text{[S ]}\text{o =}\text{Cs In[M]}\text{[M] o}$

which is applicable to homopolymerization. This paper reports the first direct experimental testing of the validity of these equations. Gas/liquid chromatographic measurement of residual substrate concentration as a function of monomer removal, measured dilatometrically for the systems methyl acrylate/styrene/bromotrichloromethane and methyl methacrylate/styrene/bromotrichloromethane has been carried out. Results indicate that the equations accurately describe the course of the reaction and permit evaluation of the appropriate transfer constant.     

Structure of the hard segments in polyurethane elastomers

A new model is proposed for the chain conformation and packing of MDI-butandiol hard segments in polyurethane elastomers. The model is based on the structure of methanol-capped MDI (MeMMe), which we have recently determined by single-crystal X-ray methods. Planar zig-zag -CH₂CH₂-sections connect successive MeMMe units, which have the same conformation as in the monomer structure. Successive monomer units along the chain are related by a centre of symmetry at the central CH₂CH₂ bond. The chains are linked together in stacks through CO…HN hydrogen bonds which involve half of the urethane groups. The remaining urethanes are similarly hydrogen-bonded to adjacent stacks, and thus the structure is stabilized by hydrogen-bonding in both directions perpendicular to the chain axis. A triclinic unit cell is proposed for the structure with approximate dimensions $\text{a = 5.2}\text{A}\text{?}$, $\text{b = 4.8}\text{A}\text{?}$, $\text{c = 35.0}\text{A}\text{?}$, α = 115°, β = 121° and γ = 85°. The space group is P1 and the cell contains two repeat units of a single chain.     

Non-classical free-radical polymerization: 3. Diffusion-control in degradative addition

The different kinetic features associated with polymerizations in which retardation arises through degradative transfer and degradative addition processes are considered. Reasons are given for believing that in reactions retarded by degradative transfer neglect of the interaction between ‘inactive’ radicals is justifiable, while with degradative addition this is not so. A kinetic treatment of the latter is developed in which all three termination reactions between propagating and inactive radicals are assumed to be diffusion-controlled with a single rate coefficient and equations are derived which permit from experimental data on rates of polymerization estimation of the definitive kinetic parameters $\text{k}{}_{\mathrm{p}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$, $\text{k}{}_{\mathrm{pm}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ and $\text{k}{}_{\mathrm{fm}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ (k_p, k′_t, k_pm, k_fm are the rate coefficients of propagation, termination, reinitiation and degradative additions, respectively). The kinetic equations are satisfactorily consistent with ew experimental data on the polymerization of 1-vinylimidazole in ethanol solution at 70°C, for which there is strong evidence for the occurrence of degradative addition. A modified procedure for processing data for polymerizations with degradative transfer is put forward which is convenient for estimating the kinetic parameters and reveals in a simple manner the importance of re-initiation. It is suggested that this treatment could be generally useful in the early stages of the study of a retarded polymerization.     

Flow birefringence studies of polymer conformation: cellulose tricarbanilate in two characteristic solvents

Flow birefringence measurements are reported on ten samples of cellulose tricarbanilate (14.1 × 10³ < M < 2180 × 10³). Phenyl benzoate, dioxane and mixtures of both were used as solvents. The ratio of Maxwell constant to intrinsic viscosity $\text{[n]}\text{[η]}$ strongly depends on temperature and kind of solvent. In ether solvents this polymer has a stiffer conformation than in an ester or a ketone. With the aid of the theory of Gotlib and Svetlov quantitative conclusions about chain stiffness can be drawn from the observed molecular weight dependence of $\text{[n]}\text{[η]}$. A number of 50 monomer units per random link were obtained in dioxane at 25°C. This agrees quite well with light scattering and intrinsic viscosity data. According to Burchard an interpretation of the great chain stiffness of this polymer in ether solvents can be given in terms of the formation of intramolecular hydrogen bonds. The tremendous influence of a change in stiffness on $\text{[n]}\text{[η]}$ must be ascribed to the varying sterical hindrance of rotation of the phenyl rings in the side groups of the chain. Unfortunately, no valuable information with respect to chain stiffening can be deduced from extinction angle data. Relatively small effects, as expected from theory, are almost completely masked by the influence of the polydispersity of the samples.     

Concentration dependence of the primitive path step length

Recent experiments by Donald and Kramer have measured the extension ratio, λ_craze, for polymers in crazes under tensile strain. In this paper it is shown that $\text{λ}{}_{\mathrm{<mtext>craze</mtext>}}\text{∝I}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{<mtext>e</mtext>}}\text{i}$ where I_e is the average contour length between entanglements in glassy, and not permanently crosslinked polymers and is obtained from melt elasticity experiments. It is also shown that I, the Rouse chain step length for a molten polymer, is independent of monomer density and that the average distance between entanglements, d ∝ ?^?α, where ? is the number of monomers per unit volume with $\text{1}\text{4}\text{? α ?}\text{1}\text{2}$. Finally these results are shown to provide confirmation for the configurational assumptions of the primitive path for reptation in which α appears as the determining factor for the concentration dependence of the relaxation modulus, the steady state viscosity and terminal relaxation time.     

Synthesis of block copolymers by a low-temperature free-radical mechanism using systems of the polystyrylaluminium-peroxide type

Block copolymers of styrene and a polar monomer (acrylates, methacrylates and acrylonitrile) can be synthesized at low temperatures (20° to minus 20°C) by a free-radical mechanism using initiating systems of the type: polystyrylaluminium (poly St-Al)-peroxide. The degree of polymerization ($\text{P}\text{?}{}_{\mathrm{n}}$) of the styryl substituent in the polySt-Al component had values 30, 300, 450 and 800. Benzoyl peroxide and dicyclohexylperoxydicarbonate were used as peroxide components. The effect of the concentration and nature of the components of the initiating system, catalytic amounts of the additional electron donor component, pyridine, and temperature on the kinetics of the process were investigated. The kinetic dependence makes it possible to consider the formation of free radicals in terms of the donor-acceptor reactions in which all the components of the system including the monomer take part. Synthesis of a block copolymer with MMA was taken as an example to show the relationships between the conditions of the process and the characteristics of the product. The data on molecular weight distribution (MW D) and the compositional distribution according to MW (pyrolysis and gel permeation chromatography) show that the main product is the ABA block copolymer where A is the styrene block and B is the MMA block. This structure is formed owing to the conditions of the process: initiation by polystyryl radical and recombination as the dominant chain termination mechanism. This structure cannot be formed under the conditions of anionic or radical (polyperoxide) initiation.     

Synthesis and conformation studies of copolypeptides composed of γ-methyl-l-glutamate and ε-N-carbobenzyloxy-l-lysine

Copolypeptides (PMGCL) composed of γ-methyl-l-glutamate(MLG) and $\text{?-N-}\text{carbobenzyloxy-}\text{l}\text{-lysine(CBL)}$ covering the whole range of copolymer composition were synthesized by the N-carboxyanhydride (NCA) method. The experimentally obtained monomer reactivity ratios were r₁(MLG)=2·0±0·4 and r₂(CBL)=0·5±0·1, from which the fractions of monomer dyads and triads in copolymer were plotted against the initial comonomer composition. From experimental results on thermally induced coil-to-helix transition of the copolypeptides in dichloroacetic acid/1,2-dichloroethane (DCA-DCE) systems, it has been found that these copolypeptides can exist in the α-helix conformation in the same manner as homopolypeptides PMLG and PCBL. The van't Hoff heat of transition ΔH showed a minimum against the initial monomer composition. The enthalpy ΔH_res of formation of intramolecular hydrogen bonds per peptide bond also showed a minimum against copolymer composition. Such behaviour on ΔH and ΔH_res was also found for copolypeptide (PBGCL) composed of γ-benzyl-l-glutamate(BLG) and $\text{?-N-}\text{carbobenzyloxy-}\text{l}\text{-lysine(CBL)}$ in DCA-DCE systems reported in a previous paper. The presence of a minimum in these relationships may be attributed to specific interactions between the side chain of one comonomer and that of the other comonomer in a two component copolymer. It is also pointed out that these copolymer molecules can exist in the α-helix conformation in the solid state.     

Carbon dioxide absorption by turbulent plunging jets of water

The absorption process as taking place in a plunging jet system is investigated. Starting from the assumption that the site of the main mass transfer process is the submerged biphasic jet, a physical model is developed and a mass transfer equation is established.In the second section of the paper, a criterial correlation eqn (35):Sh* = 8.8 (Re. We. Sc. $\text{H}\text{d}{}_{\mathrm{N}}$)^{$\text{1}\text{2}$} for the liquid phase mass transfer coefficients in the system carbon dioxide-water is obtained, on basis of experiments in which the nozzle diameter, jet velocity, jet length through the gas phase and working temperature were varied.This equation correlates in a satisfactory manner the experimental data (the average of the absolute deviation is 14.1%).     

Cyclization dynamics of polymers: 10 Synthesis,fractionation, and fluorescent spectroscopy of pyrene end-capped polystyrenes

The rate constant for end-to-end cyclization (k₁) for polymer chains is predicted to decrease sensitively with increasing chain length. In this paper the techniques are examined critically for extracting values of k₁ from experiments involving intramolecular pyrene excimer formation in polymers of the form pyrene-polystyrene-pyrene. For significance, results require samples of appropriately narrow molecular weight distribution ($\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{</ 1.13}$), as well as corrections for polydispersity differences among the samples. Particular attention is focussed both on experimental techniques and on the models used to interpret the kinetics of intramolecular pyrene excimer formation.     

Probing the reaction kinetics of vinyl acetate free radical polymerization via living free radical polymerization (MADIX)

Living free radical polymerization technology (macromolecular design via the interchange of xanthates (MADIX)) was applied to give accesses to chain length and conversion dependent termination rate coefficients of vinyl acetate (VAc) at 80 °C using the MADIX agent 2-ethoxythiocarbonylsulfanyl-propionic acid methyl ester (EPAME). The kinetic data were verified and probed by simulations using the PREDICI^® modelling package. The reversible addition-fragmentation transfer (RAFT) chain length dependent termination (CLD-T) methodology can be applied using a monomer reaction order of unity, since VAc displays significantly lower monomer reaction orders than those observed in acrylate systems (ω(VAc, 80 °C)=1.17±0.05). The observed monomer reaction order for VAc is assigned to chain length dependent termination and a low presence of transfer reactions. The α value for the chain length regime of log(i)=1.25−3.25 (in the often employed expression ) reads 0.09±0.05 at low monomer to polymer conversion (10%) and increases significantly towards larger conversions (α=0.55±0.05 at 80%). Concomitantly with a lesser amount of midchain radicals, the chain length dependence of k_t is significantly less pronounced in the VAc system than in the corresponding acrylate systems under identical reaction conditions. The RAFT(MADIX)-CLD-T technique also allows for mapping of k_t as a function of conversion at constant chain lengths. Similar to observations made earlier with methyl acrylate, the decrease of k_t with conversion is more pronounced at increased chain lengths, with a strong decrease in k_t exceeding two logarithmic units from 10 to 80% conversion at chain lengths exceeding 1800.     

Isothermal crystallization of poly(ethylene-terephthalate) of low molecular weight by differential scanning calorimetry: 1. Crystallization kinetics

The isothermal crystallization of poly(ethylene-terephthalate) (PETP) fractions, from the melt, was investigated using differential scanning calorimetry (d.s.c.). The molecular weight range of the fractions was from 5300–11750. Crystallization temperatures were from 498–513 K. The dependence of molecular weight and undercooling on several crystallization parameters has been observed. Either maxima or minima appear at a molecular weight of about 9000, depending on the crystallization temperature. The activation energy values point to the possibility of different mechanisms of crystallization according to the chain length. A folded chain process for the higher $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ chains and an extended chain mechanism for the lower $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ chains. The values of the Avrami equation exponent n vary from 2–4 depending on the crystallization temperature; non-integer values are indicative of heterogeneous nucleation. The rate constant K depends on T_c and $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$, showing maxima related to the T_c used. The plot of log K either vs. (ΔT)^?1 and (ΔT)^?2 or $\text{T}{}_{\mathrm{<mtext>m</mtext>}}\text{T(ΔT)}$ and $\text{T}{}^2{}_{\mathrm{<mtext>m</mtext>}}\text{T(ΔT)}{}^2$ is linear in every case.     

Nucleophilic substitution onto poly(methylmethacrylate): 4. Dilute solution properties of substituted polymethacrylates

The morphological and hydrodynamic properties of a series of homogeneous fractions of substituted poly(methylmethacrylate) (A units) bearing keto-β-functional groups (B units) of the general structureCOCH₂R, with R = SO_xCH₃ (x = 1,2) or SO₂N(CH₃)₂, were investigated by intrinsic viscosity, light scattering and partial specific volume measurements in dimethylformamide (DMF) solution at 25°C. For molar substitution degrees $\text{DS}{}_{\mathrm{m}}\text{< 0.5}$, the copolymers behave as flexible random coils. The Stockmayer-Fixman-Yamakawa analysis of the $\text{[η]-}\text{M}\text{?}{}_{\mathrm{w}}$ data leads to slightly higher unperturbed dimensions K_o and steric factor σ than those for PMMA, and to stronger chain expansion as a result of the weak hydrogen bonding between DMF and COCH₂R units and a positive X_AB interaction parameter. For $\text{DS}{}_{\mathrm{m}}\text{> 0.5}$ however, copolymers bearing COCH₂SO₂N(CH₃)₂ groups behave as worm-like chains, as derived from the Fujii-Yamakawa analysis of the $\text{[η]-}\text{M}\text{?}{}_{\mathrm{w}}\text{-}\text{v}\text{?}$ data: the persistence length increases from 380 to 570 Å within the $\text{DS}$_m range 0.57–0.75. This transition from a random coil to a worm-like chain for $\text{DS}{}_{\mathrm{m}}\text{> 0.5}$ was tentatively correlated with the accumulation of B units in sterically hindered and self-associated short blocks of average length l_B ? 1.6 which provide drastically increased rigidity to the copolymer chain.     

Molecular weight distributions in novolactype phenol-formaldehyde polymerization

To model the reversible novolac polymerization, five reactive species A to E have been defined. Molecules having bound CH₂OH (Q_n) are distinguished from those without it (P_n) and it is assumed that molecules of Q_n do not have more than one bound CH₂OH group. A kinetic model has been written and, based upon it, balance equations for molecules of novolac polymer in batch reactors have been derived. Based upon our earlier studies, the phenomenon of molecular shielding has been neglected. As a result, the reactivities of the ortho and para positions of phenol which are available in the literature could be used. The kinetic model for the molecular weight distribution (MWD) of reversible novolac polymer formation thus involves only one parameter. The study of the MWD of novolac polymer reveals two very important design variables: the phenol-formaldehyde ratio, $\text{[P]}{}_0\text{[F]}{}_0$, in the feed and the vacuum applied on the reactor. As the $\text{[P]}{}_0\text{[F]}{}_0$ ratio is increased, the breadth of the distribution is found to increase and it undergoes a maximum at $\text{[P]}{}_0\text{[F]}{}_0\text{? 1.4}$ for the set of rate constants chosen. At this ratio, the chain length average molecular weight is also found to be the largest. Industrially, the $\text{[P]}{}_0\text{[F]}{}_0$ ratio used in producing novolac polymer is 1.67 and it is usually desired that the polymer be linear with minimal branching. On application of vacuum, for a given time of polymerization, the chain length molecular weight is found to increase when the results are compared with those of batch reactors. The breadth of the distribution is also found to reduce thus giving a lower polydispersity index of the polymer formed.     

Simulation of cyclics and degradation product formation in polyethylene terephthalate reactors

The second stage of a batch polyethylene terephthalate (PET) reactor with a kinetic scheme consisting of side reactions like thermal degradation, redistribution, cyclization and reaction with monofunctional compounds (cetyl alcohol), in addition to the major polycondensation step, has been simulated. The cyclization equilibrium has been shown by Semlyen for various cyclic compounds to be chain-length-dependent¹. Mass balance for various side products and the polymer, PET, have been carefully worked out and the resulting set of differential equations have been solved for the molecular weight distribution (MWD) of the polymer. It is found that the cyclization reaction has considerable effect on the polydispersity index of the polymer even though the total quantity of cyclic compound is no more than 5%. The effect of variation of temperature and initial concentration of monofunctional compound was found to have little influence on the polydispersity index of the polymer. Since the removal of the condensation product does not become diffusion-controlled till the average chain length of the polymer reaches the value of 30, the reaction mass can be assumed to attain a uniform ethylene glycol concentration for a given applied vacuum and can be determined by the vapour-liquid equilibrium relation. The fractional level of ethylene glycol concentration, $\text{[}\text{G}\text{] (≡}\text{[}\text{EG}\text{]}\text{[}\text{P}{}_1\text{]}{}_0\text{)}$, has been taken as a parameter and the MWD results were found to vary the redistribution rate constant with sensitivity increasing with decreasing [G]. It was shown that the importance of the redistribution reaction is increased when the cyclization reaction also occurs.     

Syntheses and properties of tetramethyl-p-silphenylenesiloxanealkenylmethyl-siloxane copolymers and their derivatives

$\text{Tetramethyl}\text{-p-}\text{silphenylenesiloxane}\text{alkenylmethylsiloxane}$ (TMPS/AMS) copolymers were snyhtesized from p-bis-dimethylhydroxysilylbenzene and a series of alkenylmethyldichlorosilanes as the starting materials. The alkenyl groups of the copolymers were vinyl, allyl, 2-(3-cyclohexenyl)ethyl, methacryloxypropyl and 3-bicycloheptenyl groups. The composition ranged from TMPS/AMS mole% ratio of $\text{92}\text{8}$ to $\text{83}\text{17}$ and the molecular weights were in the range 10⁴ to 10⁵. These copolymers were confirmed to have two compositions, one a certain length of TMPS segment and the other an AMS monomer unit, and that they could form films on the basis of the crystallization character of the TMPS segment. The melting temperatures of these copolymers decreased as the TMPS mole content decreased and as the alkenyl group contents were increased. The epoxidation reactions of these copolymers with m-chloroperbenzoic acid were carried out and the proportions of conversions of the alkenyl groups into epoxy groups varied depending upon the types of alkenyl groups involved. Cyclic olefin groups such as the 2-(3-cyclohexenyl)ethyl or the 3-bicycloheptenyl group were more easily epoxidized than the vinyl or allyl groups. The TMPS/dimethylsiloxane (DMS) graft copolymer could also be synthesized by the reaction of TMPS/vinylmethylsiloxane copolymer with dimethylhydrosilyl-terminated DMS oligomer in the presence of chloroplatinic acid acting as the catalyst.     

Thermal and mechanical properties of tetramethyl-p-silphenylenesiloxanedimethylsiloxane block copolymer

Several kinds of $\text{tetramethyl}\text{-p-}\text{silphenylenesiloxane}\text{dimethylsiloxane}$ (TMPS/DMS) block copolymers having various compositions and segment lengths were synthesized by the polycondensation of p-bis(dimethylhydroxysilyl)benzene and silanol-terminated DMS oligomers of different degrees of polymerization, which were 19, 43, 300, 380 and 540 DMS monomer units. The compositions ranged from TMPS/DMS wt% ratio of 100/0 to 24/76. For these copolymers, differential scanning calorimetry was carried out to determine the melting temperatures, the heat of fusion and the crystallinities. The melting temperatures and the crystallinities of the block copolymers were found to decrease as DMS contents were increased from 11 to 76 wt% and as DMS segment lengths were decreased from 540 to 19. The crystalline parts of TMPS segment would be increased according to the long TMPS sequences which were obtained from the copolymerizations by using DMS oligomers with high degrees of polymerization such as 300, 380 and 540. The stress-strain behaviour and the dynamic mechanical behaviour were also investigated for these copolymers. The tensile strength was decreased and the percentage elongation was increased with increasing DMS content and segment length. In the case of the copolymers for which the DMS contents remained constant at 26 wt%, two major transitions were observed at around ?120° and ?10°C for the copolymers having DMS block sizes of 300, 380 and 540. But for the copolymers having those of 19 and 43 the two transitions merged together at ?50°C. The relaxations at ?120°C corresponding to the glass transition of DMS component and those at ?10°C are due to the amorphous TMPS phase which is separated from the DMS phase owing to the longer sequence length. The relaxation observed around ?50°C is due to the shorter sequence length of TMPS in the main chain plus the presence of more flexible DMS component. It may be suggested that the long sequence length causes large domains of hard and soft phases which consist of TMPS and DMS blocks respectively.     

A study of the rates of catalyzed Boudouard reaction

The rate of Boudouard (C-CO₂) reaction catalyzed by Li₂O and Li₂CO₃ was investigated in the temperature range 839°–1050°C. The rate data is reported in the form of Fractional burn-off (F) vs time (t) plots. The experimental rate constant (K) data deduced from the initial linear region of these plots is represented by $\text{log K = 2.901(±0.186) ?}\text{22,240(±1,020)}\text{2.303RT}$; K is in gm/gm min. The experimental rate constant data was corrected for pore-diffusion and film mass transfer effects. The intrinsic rate constant (K_v) was found to exhibit the following temperature-dependence: $\text{log K}{}_{\mathrm{v}}\text{= 5.471(±0.353) ?}\text{48,040(±1,920)}\text{2.303RT}$; K_v is in moles/cm³atm sec. An electrochemical mechanism was proposed to explain the catalytic activities of Li₂O and Li₂CO₃.