Investigation of the factors causing chain structure change in ionic diene polymerization

Ether‐induced isomerization of crotyllithium to 3‐lithium‐butene‐1 may be regarded as a model of reactions taking place in the chain growth process during organolithium initiated diene polymerization. In this reaction, as is well known, ethers and other complexating agents considerably increase the number of 1,2‐ (and 3,4‐) links in the chain. Various ionic type catalysts (organoaluminum compounds, titanium halides, hydrogen halides) induce the cis‐trans isomerization of units of the polymer chain (natural rubber) at low temperatures. The process is accompanied by a significant fall in degree of unsaturation of the polymer. The oxidation of Ti3+ to Ti4+ under the influence of peroxides is accompanied by the formation of free radicals, initiating low temperature polymerization of monomers or structuration of rubbers. The oxidation of Ti3+ to Ti4+ effected by hydroperoxides in hydrocarbon media is also accompanied by radical reactions, leading to oxidation and degradation of the polymers. These secondary reactions are depressed by the conventional inhibitors of radical reactions. Alkylaluminumhalides formed during interaction of alkylaluminumnitrites with halides of variable valency metals are efficient cationic catalysts, inducing the polymerization of isobutylene and (3,3‐bischloromethyl)oxacyclobutane. During polymerization of butadiene and isoprene in the presence of alkylaluminumchloride, amorphous, insoluble polymers are formed with very high softening temperatures (410 and 370°C, respectively). Similar conversions are undergone by natural rubber in solution under the influence of titanium tetrachloride and alkylaluminumchloride. Under the action of alkylmagnesium halides 1,4‐polybutadiene in solution shows a considerable loss in degree of unsaturation and an elevation of the glass temperature, preserving at the same time its solubility, which evidently is due to the occurrence of intramolecular cyclization at the diallyl links. Apparently associated with such processes is the diminished unsaturation of sodium butadiene rubber (ca. 85% of the theoretical). L'isomérisation de lithiumcrotyle en 3‐lithium‐1‐butène sous l'influence des éthers peut ětre considérée comme modèle pour les réactions qui se déroulent dans le processus de la croissance des chaǐnes pendant la polymérisation des diènes sous l'influence des organolithiens. On sait que dans le dernier cas les éthers et d'autres composés formant les complexes augmentent considérablement la quantité 1,