THERMAL-STABILITY OF MOLECULARLY UNIFORM OLIGOURETHANES BASED ON 1,5-NAPHTHALENE DIISOCYANATE AND 1,4-BUTANEDIOL

The thermal stability of molecularly uniform oligourethanes based on 1 ,5-naphthalene diisocyanate (NDI) and 1,4-butanediol (BDO), which serv ed as model compounds for the hard segment domains of technologically relevant NDI-based polyurethane (PUR) elastomers, was investigated by a series of complementary analytical methods. The NDI/BDO oligourethan es were characterized by high melting points above 250 degrees C, so t hat thermal decomposition interfered with the melting process. The dec omposition could be associated with the disruption of hydrogen bonds b etween the urethane NH and CO groups and proceeded in the disordered r egions of the microcrystalline oligomers; this was also reflected from the end group effect on the melting. The temperature Limit for the th ermal stability of the urethane linkage in the crystalline state was a bout 230 degrees C. For disordered regions, retro-urethanization react ions were already observed beginning at temperatures in the range of 2 10 degrees C. The generated free isocyanate formed allophanate crossli nks, and with increasing temperature carbodiimide formation and conver sion into polymeric carbodiimide structures were observed.