1,2-Diisocyanates were cyclopolymerized using CpTiCl(2)N(CH3)(2). Treatment of 1,2-diisocyanatodecane with CpTiCl(2)N(CH3)(2) in THF effected its cyclopolymerization with stoichiometric control over molecular weight and with M(w)/M(n) ranging from 1.2 to 1.8. IR, H-1 NMR, and C-13 NMR spectra of the resulting polymers indicate that the monomer underwent complete cyclization. Studies of the solution properties of poly(1,2-diisocyanatodecane) showed that it maintains a smaller hydrodynamic volume than poly(n-hexyl isocyanate) at equivalent molecular weights. Living poly(n-hexyl isocyanate) mas end-capped with blocks of poly(1,2-diisocyanatopropane) and poly(1,2-diisocyanatodecane). TGA and DSC studies of these block copolymers showed that the individual block segments decomposed at the same temperatures as their respective homopolymers. Random copolymerizations of n-hexyl isocyanate with 1,2-diisocyanatopropane and 1,2-diisocyanatodecane were conducted. TGA studies of these macromolecules showed that the decomposition temperature of the copolymer was a function of its 1,2-diisocyanate content, and the incorporation of a relatively high mole percent of the diisocyanate monomer was necessary to observe an increase in the decomposition onset of the copolymer.