An alternating boration copolymerization methodology was explored by making use of different boration reactivities between diynes and diisocyanates. This method affords a synthetic route for novel type of organoboron polymers having monomeric iminoborane units in their main chain. The polymers obtained were soluble in commom organic solvents such as tetrahydrofuran, chloroform, and benzene. Gel permeation chromatographic analysis showed that their number-average molecular weights were several thousands. The treatment of 1,4-diethynylbenzene with two equimolar amounts of diphenylbromoborane (in CHCl3 at room temperature; selective haloboration) followed by reaction with diisocyanates (in CHCl3 at room temperature; phenylboration polymerization) gave the corresponding polymers in moderate yields. Particularly, the polymer prepared from aromatic monomers showed high air stability. In addition, fully aromatic organoboron polymers can be regarded as a novel type of conjugated polymer via B-N bonds having a double bond nature due to a well-established psc-px interaction.