HYDROBORATION POLYMERIZATION OF DICYANO COMPOUNDS .2. REACTIONS OF ISOPHTHALONITRILE WITH PRIMARY OR SECONDARY ALKYLBORANE

The steric effects of the alkyl substituents on the monoalkylborane monomers in hydroboration polymerization of dicyano compounds were examined. t-BuBH2.NMe3 gave the corresponding poly(cyclodiborazane)s by the reaction with aromatic dicyano compounds such as terephthalonitrile or isophthalonitrile. When less sterically hindered n-BuBH2.NMe3 was used as a monomer, the polymerization with isophthalonitrile resulted in gelation due to the further hydroboration reaction of initially formed iminoborane species. On the other hand, i-PrBH2.NMe3 gave the soluble polymers, which showed, however, lower molecular weights in comparison with those from t-BuBH2.NMe3. From these results, hindered alkyl groups in monoalkylboranes were found to play an important role to prevent side reactions in hydroboration polymerization of dicyano compounds.