Studies on the kinetics of ceric-thiourea initiated aqueous polymerization of methyl methacrylate—II. Mechanistic features in strongly acid solutions

The kinetics of ceric-thiourea initiated aqueous polymerization of methyl methacrylate in 1 M H₂SO₄ have been studied. Ceric ion and thiourea initially form an 1:1 complex which then reacts with uncomplexed ceric ion to form the initiating thiocarbamido radicals. The termination is predominantly biomolecular below an initial ceric concentration of 0.66 × 10^?2 M (depending upon the rate of initiation). At higher initial ceric concentrations, polymer radicals are terminated overwhelmingly by ceric ions. Substituted thioureas reduce the rate of polymerization according to the order of increasing electron density on the sulphur atom. The overall activation energy of polymerization is 12.1 kcal/mol in the region of bimolecular termination and 10.2 kcal/mol in the region of metal ion termination.     

The sequence length in polymethyl methacrylate

The sequence length and tacticity of methyl methacrylate polymers prepared at 303–363°K in the presence of trichlorobromomethane as a transfer agent were measured from NMR spectra. The lengths did not change appreciably but there was an increase in syndiotacticity with increasing concentration of transfer agent. There is no marked change in tacticity with molecular weight.     

Non-ideality in vinyl polymerization—VI: Polymerization of methyl methacrylate initiated by benzoyl peroxide

The polymerization of methyl methacrylate in benzene was initiated by benzoyl peroxide and examined by kinetic analysis particularly from the point of view of primary radical termination. It is concluded that the velocity constant for dissociation of the benzoyloxy radical to give the phenyl radical is affected by the nature of the medium.     

Activation of radical polymerization by microwaves—I. Polymerization of 2-hydroxyethyl methacrylate

2-Hydroxyethylmethacrylate (HEMA) in bulk without any radical initiator is treated with a polarized microwave beam (2.45 GHz) inside a wave guide at various electrical powers (P₀). The fluid monomer polymerizes finally to form a solid material. The various steps of the reaction of polymerization are described through study of the variation with time of the temperature of the sample and of the part (P_u) of the electrical power (P₀) degraded in the polymerizable medium because of dielectric loss.     

The transparency of polyurethane-poly(methyl methacrylate) interpenetrating and semi-interpenetrating polymer networks

Various combinations of polyurethane (PUR) and poly(methyl methacrylate) (PMMA) were prepared as interpenetrating polymer networks (IPN) or semi-IPNs. In the latter, either the PUR or the PMMA component was crosslinked. The optical transmissions of these materials were measured as a function of the crosslink degrees of both phases. The role of the PUR chain extender, poly(oxypropylene) glycol, is discussed. It is concluded that any means which increases the degree of phase dispersion favours the transparency of PUR/PMMA based IPNs and semi-IPNs.     

Co-nonsolvent systems for poly(ϵ-caprolactone) and poly(methyl methacrylate)

The cloud points for the co-nonsolvent systems (i) pyridine (PY) + formic acid (FA) towards poly(?-caprolactone) (PCL) or poly(methyl methacrylate) (PMMA) and (ii) pyridine + acetic acid (AA) towards PCL have been experimentally determined as a function of solvent composition at fixed polymer concentrations. Heats of mixing for the (FA + PY) system have also been measured. The single liquid approximation model correctly predicts for the (PY + FA) system the solvent composition at which the solvent power of the mixture is the poorest, provided it is recognized that the solvent system is comprised of pyridinium formate (PYFA) as one component and either PY or FA (depending on which is present in excess over 1:1 mole ratio) as the other. With the other co-nonsolvent system, the prediction is not as good. A possible reason for the discrepancy has been given.     

The kinetics of the polymerization of methyl methacrylate initiated by t-butylmagnesium bromide in THF,toluene or mixed solvent

The kinetics of the solution polymerization of methyl methacrylate in THF, toluene and their mixtures were studied between 200 and 300 K using dilatometry (in the systems where it was valid), gravimetric determination and monitoring monomer and polymer concentrations by NMR spectrometry. The reaction followed zero order kinetics at 200 K, first order kinetics at 275 K and mixed order in between. At both the limits and intermediate range, the reaction followed an integrated rate equation consistent with terminationless propagation proceeding through a complex between monomer and the propagating species. Above 275 K, termination and side reactions were evident and the yields of high mol. wt polymer were small. Density-temperature calibrations for monomer in THF, toluene and mixtures were constructed for the range 190–283 K. However for polymerizations in toluene-rich mixtures, where very high mol. wt polymer forms, the contraction did not correlate linearly with conversion.     

Polysilane derivatives of the transition metals II. The crystal and molecular structure of [tris(trimethylsilyl)silyl]pentacarbonylmanganese, (Me3Si)3SiMn(CO)5

The crystal and molecular structures of [tris(trimethylsilyl)silyl]pentacarbonylmanganese, (Me₃Si)₃SiMn(CO)₅, have been determined from three-dimensional X-ray data obtained by counter methods. The compound crystallizes in space group P$\text{1}$ of the triclinic system, with two molecules in a unit cell of dimensions: a = 9.002(2), b = 9.655(2), c = 15.639(3) Å, α = 83.66(1), β = 105.65(1), γ = 114.61(1)°.The observed and calculated densities are 1.20 (±0.03) and 1.23 g-cm^?3 respectively. Full-matrix least-squares refinement of the structure has led to a final value of the conventional R factor of 0.059 for the 818 independent reflections having F² > 3σ(F²).The coordination geometry about the manganese atom is approximately octahedral and, about the silicon atom bonded to the manganese atom, tetrahedral.The relative orientations of carbonyl and trimethylsilyl groups, when viewed down the MnSi bond, appear consistent with minimization of energy due to nonbonded interactions.Two of the equatorial carbonyl groups are displaced out of the equatorial plane towards the silicon ligand by 6°. The SiMn bond is 2.564(6) Å long and has no multiple character.     

Determination of different manganese ions in ammonium dihydrogen phosphate (ADP) monocrystals

Conditions for determining concentrations of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions in ammonium dihydrogen phosphate (ADP) monocrystals were investigated. The amounts of the incorporated manganese ion species depend on the total amount of manganese in the ADP solutions, on the ratio of the amount of dissolved permanganate and manganese(II) salts, and on the acidity of the solution.     

Pyrolysis—gas chromatography of methyl methacrylate—styrene and methyl methacrylate—α-methylstyrene copolymers

The pyrolysis—gas chromatographic behaviour of methyl methacrylate copolymers with styrene or α-methylstyrene was investigated with a Curie-point pyrolyzer. Monomer yield from each copolymer was very high as a result of the high probability of unzipping. Though only small quantities of dimers and or trimers are formed on the pyrolysis of two copolymers, they reflect the sequence distribution of copolymers. Under some assumption, the run number of each copolymer is calculated using the amounts of dimer and or trimer formed.     

A comparative study of polyurethane-poly(methyl methacrylate) interpenetrating and semi-1 interpenetrating polymer networks

Polyurethane(PUR)-poly(methyl methacrylate) (PAc) semi-1 interpenetrating polymer networks of various compositions have been prepared. They show several differences from the corresponding full IPN's. Thus, the rate of polymerization of the acrylic phase is lower. Transparent plates are also more difficult to obtain. Both effects are ascribed to the absence of the crosslinking agent of the second phase. The composition also plays a role in transparency. Solvent extraction shows that, with increasing PUR content, more PAc remains entrapped in the PUR network. The transition behaviour indicates that the phases are less entangled in semi-IPN's than in IPN's. Consequently, the effect of crosslinking or not crosslinking the second component is very important with regard to the properties of PUR/PAc combinations.     

Mixed ligand complexes in vinyl polymerization—II: [NN′-ethylenebis(salicylideneiminato)] (benzoylacetonato)cobalt(III) as an initiator

The polymerization of methyl methacrylate initiated by a mixed ligand complex. [NN′-ethylenebis(salicylideneiminato)](benzoylacetonato)cobalt(III) has been studied in bulk and in benzene at 70° and 80°. The rate of polymerization is proportional to (concentration of the chelate)${}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and the monomer exponent is close to 1.5. The activation energy and the kinetic and transfer constants are evaluated. A free radical mechanism has been proposed.     

The effect of temperature on the extraction of plutonium(IV) from nitric acid by tri-n-butyl phosphate

The extraction of Pu(VI) from varying concentration of nitric acid into TBP in dodecane was studied at different temperatures in the range 20–60°C. From the distribution coefficient data, the enthalpy changes for the extraction of Pu(VI) under different conditions were determined. All the data obtained showed that the extraction of Pu(VI) from nitric acid into TBP is exothermic in nature. An attempt was made to evaluate the thermodynamic free energy and entropy changes.     

Studies on the kinetics of polymerization of vinyl acetate by benzoyl peroxide at 60° using pyridine as solvent

Kinetics of Bz₂O₂-initiated polymerization of VAC in pyridine at 60° were investigated. The polymerization was significantly retarded by pyridine. The monomer exponent decreased from 2.5 at a relatively low [Bz₂O₂] (1.0 × 10^?2 M) to 2.0 at [Bz₂O₂] ? 4.0 × 10^?2 M. The observed kinetic features were explained on the basis of degradative chain transfer and copolymerization with pyridine.     

Non-ideality in vinyl polymerization—IV. Kinetics of polymerization of vinyl acetate in benzene initiated by azo-bis isobutyronitrile (AIBN)

Vinyl acetate was polymerized in bulk and in benzene at 50°C using a wide range of concentrations of azobisisobutyronitrile. Values of f_k (the efficiency of initiator) and k_prt/k_ik_p (the characteristic constant of primary radical termination) were found to be 0.53 and 2.00 × 10⁴ respectively from data for bulk polymerization. In solution polymerization, the initiator exponent is a function of initiator concentration ranging from 0.35 at high concentration to- about 0.65 at low concentration. This result has been explained on the basis of degradative chain transfer to solvent and primary radical termination. The results have been treated according to mathematical formulations already developed; the characteristic constant of degradative chain transfer and the transfer constant of the solvent have been determined. The results have been compared with literature values and discrepancies explained.     

Oxidations involving silver—IX : Oxidation of primary amines by silver(II) picolinate.

A re-examination of the oxidation of primary amines of the type R·CH₂NH₂ by silver(II) picolinate reveals that the major product is usually the nitrile RCN, rather than the aldehyde RCHO, as had been reported previously.⁴     

Mechanistic studies on the photo-oxidation of commercial poly(butadiene)

Products from both the thermal and photo-oxidation of poly-butadiene have been studied using various analytical techniques such as infra-red and ultra-violet spectroscopy, gas-liquid chromatography and phosphorescence emission and phosphorescence excitation spectroscopy. Analyses have allowed a plausible mechanism to be formulated for the photo-oxidation of this polymer, consistent with all the observed physical and chemical changes. Both photo- and thermal oxidative polymer degradation initially result in the formation of α, β-unsaturated carbonyls which, under photo-degrading conditions, are subsequently photolysed to yield the observed final products.     

Alkylation reactions with organometallic compounds : IV. The reaction of tris(triphenylphosphine)methylcobalt with diphenylacetylene

Tris(triphenylphosphine)methylcobalt;(Ph₃P)₃CoCH₃, reacts with diphenyl-acetylene to give α-methylstilbene as the sole addition product.(Ph₃P)₃CoCH₃ can be used as an alkylation reagent in ethers or in aromatic solvents.