-. I he termination mechanism in the bulk polymerization of styre~le and vinyl acetate initiated by ol,olf-azobisisobutyronitrile has been investigatetl. CM-Labelled initiators were employed and activities of salnples \yere determined by internal liquid scintillation c o~~~n t i~n g . Lleasurements of fractionated and tunfractionated polystyrene sho\ved an average of 1.94 and 2.04 tagged fragments per molecule, respectively, and indicated termination by combination a t 60" C. For polyvinyl acetate 1.06 fragments \\we found per molecule, indicating termination b3. disproportionatio~l a t 60' C.One of the features of vinyl addition reactions, which is still subject to coilsiderable uncertainty, is the inode of termination of gro\\~ing chains. I t is universally accepted that ter~nination reactions must occur as the result of the interaction of tu7o radicals, but the mechanism of this termination, whether by direct combination or by disproportionation, has only been investigated for a few systems, and has not been proved unequivocally even for these.Nevertheless the inode of termination is of primary in~portance in kinetic analysis of data, in the assignment of termination constants and the prediction of molecular weights. Unless the mode of termination is understood, these quantities are subject to an uncertainty of a factor of two.Two sensitive methods exist for the solution of this problem. Bamford and Jenltins (I) have described a technique of coupling preformed polymer possessing suitably reactive end groups. Alternatively with the use of radioactive initiators, it is possible to determine the number of initiator fragments present per polylner molecule (2, 3, 4). Since each initiator fragment found generated a chain, then in the final polymer the presence of t~v o initiator fragments per polymer nlolecule would indicate the exclusive occurrence of combination, and of one initiator fragment of disproportionation.Previous studies have not yielded completely conclusive results. For methyl methacrylate, the monomer subjected to the most intensive study, early work by Arnett and Peterson ( 5 ) using tagged initiators, indicated combination, whereas Bevington et al. (3) found a predominance of disproportionation. Ayrey and Moore (6) also found disproportionation and combination, but their results were not in exact agreement with those of Bevington.I t is reasonable to assume that for most monomers, termination reactions by colnbination and disproportionation can be considered as competitive reactions, each with a definite rate constant and activation energy. I t is our intention to investigate this problem in detail, and the present report represents our first work in this direction.The systems styrene and vinyl acetate, initiated with cr,crl-azobisisobut?;ronitrile (AIBN), were chosen for this preliminary study. E S P E R I M E S T A i L -1Iaterialscr,cr'-LAzobisisobutyronitrile (XIBN) dicyano C" was obtained from the Co~nmissariat 5 ~'~n e r~i e z4tomique, Saclay, France, and possessed a specific activity of 200 p...

The proton magnetic resonance spectrum of branched dextran contains a peak, not found in the spectrum of linear dextran, which is assigned to C1 protons a t non-1,6-linkages-linkages which in most branched dextrans form the branch points. A quantitative measure of the extent of branching-the ratio of 1,6-linkages to non-1,6-linkages-is obtained by taking the ratio of the areas of the peaks associated with these two types of linkages. The value so obtained agrees well with that obtained by periodate analysis.For polysaccharides in which the non-1,6-linkages are known t o be a t branch points, n.1n.r. spectroscopy thus affords a means of detecting and estimating branching which is more convenient than methods currently in use.

We have been studying the polymerization characteristics of styrene oxide employing the cationic initiator trityl hexachloroantimonate.' After a polymerization mixture

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Macromolecules which possess a large number of some functionality and ionize in aqueous media are called polyelectrolytes.Ionization of the attached function aids in the solubilization of the polyelectrolyte substance and is responsible for its unique properties.Although the ionogenic function may be regarded as a salt, dissolution of the polyelectrolyte substance is not comparable to the dissolution of a simple salt.A simple salt such as sodium chloride in solution produces a cation and an anion of comparable size.Each ion has independent mobility.A polyelectrolyte dissolves to yield a polyion and counter ions.The polyion holds a large number of charges in close proximity because they are attached to the macromolecular backbone.Although the polyion has mobility, the individual charges attached to the chain do not.They remain within the domain of the macromolecular coil. Not all the gegions or counterions are completely mobile. Anionic polyelectrolytes have positive counter ions whereas cationic polyelectrolytes have negative counter ions.Polyampholytes can acquire either positive or negative charge along the macromolecular backbone depending upon the composition of the solution.Pictorially, one has the following 128