The theoretical aspects of a new method of regulating the steric structure in addition polymers are treated. The basic principle utilized is the directing force at the free end of the propagating species, as contrasted to the influence of a bound initiator. Only small differences in the free energies of activation of the isotactic and syndiotactic propagations are required for relatively significant changes in polymer structure, particularly at low polymerization temperatures. Both the relative amounts of the two configurations in the polymer and the distribution of individual sequence lengths bear a simple relationship to the two propagation constants. In the analogous rotational isomerism, the free energy difference between the gauche and trans conformations is known to be influenced by both steric and electrostatic factors. For molecules of the type ACH2CH2A, the difference in heat content is increased by an increase in the size or the polarity of the substituents and, for polar substituents, by a decrease in the dielectric constant of the medium. Steric and electrostatic factors at the free end of the growing polymer chain can, in theory, influence the structure in polymers. This conclusion is based on an estimate of steric and electrostatic energy components of the most probable conformational arrangements for the isotactic and syndiotactic configurations in representative polyvinyl chloride with theoretical structure. The refinement introduced by bond angle deformation can also be approximated for the two polymer configurations. With respect to each of the three energy components the syndiotactic configuration is the preferred structure, in agreement with known experimental results that polyvinyl chloride prepared under free radical conditions does contain syndiotactic sequences sufficiently long for x‐ray detection. The combined, alternate use of the directing force at the free end of the propagating species and that of a bound initiator to form syndiotactic–isotactic block copolymers is suggested.
Cumene hydroperoxide decomposes near 100 °C. in reactive solvents but only slightly in stable solvents. The decomposition is not a simple first order reaction. The results may be interpreted as the sum of a first and a three-halves order reaction. Approximate over-all energies of activation of the decomposition determined from the data obtained for the decomposition in cumene (31 kcal. per mole), methanol (31 kcal. per mole), styrene (20 kcal. per mole), and the energy of activation for the initial unimolecular step in benzene–styrene mixtures (30.4 kcal. per mole) agree with the values reported for similar peroxides and hydroperoxides in similar solvents. The energy of activation for the radical-induced decomposition is 6.5 kcal. per mole. The data suggest that the first step of the decomposition is the unimolecular reaction involving scission of the O–O bond. If the resultant C6H5C(CH3)2O∙ radical is not reactive towards the solvent, it tends to lose either a phenyl or a methyl radical and form acetone or acetophenone respectively. The former reaction predominates. The decomposition rapidly becomes autocatalytic, particularly in cumene at higher temperatures, presumably because of the radical-induced decomposition of the hydroperoxide. The identified products of decomposition in cumene can be explained by the various reactions of the radicals formed in the mixture. The polymerization shortstop 2,5-ditertiarybutylhydroquinone reacts rapidly below 0 °C. with an equimolar weight of cumene hydroperoxide, and the resulting products retard further thermal decomposition at 90 °C. quite strongly. The shortstop 2,4-dinitrochlorobenzene does not react with cumene hydroperoxide and would seem to act merely as a powerful retarder for the decomposition at the higher temperature. The effect of other related compounds on the decomposition of cumene hydroperoxide in styrene was less marked and agrees with the relatively less effectiveness of these compounds as stoppers in emulsion copolymerization.
DECOMPOSITION OF CUMENE HYDROPEROXIDE BY FERROUS IRON 4465weighed. The amount of polymercuration so determined was added to that found by the carrier technique.Acknowledgments.-The authors gratefully acknowledge the Fellowship granted to one of us (W. K.) by the Atomic Energy Commission, and the help and cooperation of Dr. Gerhart Groetzinger of the Institute for Nuclear Studies, who bombarded the sodium bromate solution from which some of the needed BrE2 was obtained. Summary Both toluene and nitrobenzene were mercurated (a) with mercuric acetate, and (b) with mercuric perchlorate in perchloric acid solution.1. 2.The amounts of ortho and para and of meta isomers thus formed were determined in each case. The analytical method for the tolyl mercuric salts depended upon converting these compounds to bromotoluenes, and analyzing these by a tracer technique requiring BP2.It was found that mercuration with mercuric perchlorate in perchloric acid solution gave the pronounced orientation effects typical of electrophilic substitution ; mercuration with unionized mercuric acetate showed much less strongly marked orientation effects. CHICAGO, ILLISOISRECEIVED MARCH 18, 1950 3.In most low temperature free radical initiated emulsion polymerization recipes the initiating free radicals are formed by the reaction between cumene hydroperoxide (CHP, CBH~C(CH~)~OOH) .
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