ON THE ANIONIC-POLYMERIZATION OF (DIALKYLAMINO)ISOPRENES .2. INFLUENCE OF THE TERTIARY AMINO GROUP ON THE POLYMER MICROSTRUCTURE

The anionic polymerization of 5-(N,N-dialkylamino) isoprenes carrying various alkyl substituents was studied in nonpolar (benzene, hexane) a nd polar solvents (tetrahydrofuran, dioxane, triethylamine). The micro structure is found to be strongly dependent on the bulkiness of the te rtiary amino group. All polymerizations in nonpolar solvents occur by a 4,1-addition of the monomer to the anionic chain end. In THF no poly merization occurs. The results are discussed with respect to the stere oelectronic situation at the growing chain end. For monomers with the most bulky branched side groups (isopropyl, isobutyl, and 2,6-cis-dime thylpiperidyl) the addition is not only regioselective but also stereo selective, giving rise to the formation of stereoregular polymers with cis-4,1-repeating units. In the case of monomers with linear, less bu lky alkyl substituents (e.g. ethyl, propyl, butyl, or piperidyl), the polymer contains a mixture of cis- and trans-4,1-units (until about 70 %). In all cases the amount of 4,3-units is less than in the anionic p olymerization of isoprene, despite the fact that the aminoisoprenes ha ve a polarity comparable to triethylamine.